RENOVATION OF BUILDINGS USING STEEL TECHNOLOGIES...

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Research Programme of the Research Fund for Coal and Steel STEEL RTD

Project carried out with a financial grant of the Research Programme of the

Research Fund for Coal and Steel DRAFT FINAL REPORT

Technical Report No 7, issued March 2011, updated October 2011

Period of Reference 01 July 2007 to 30 June 2010

Technical Group TGS8

RENOVATION OF BUILDINGS USING STEEL TECHNOLOGIES (ROBUST)

Grant Agreement No. RFSR-CT-2007-0043

The Steel Construction Institute (SCI) Silwood Park, Ascot, Berks, SL5 7QN, United Kingdom with Sub-contractors Oxford Brookes University (OBU) Department of Architecture, School of the Built Environment, Oxford Brookes University, Gipsy Lane Campus Oxford OX3 0BP

RWTH Aachen Lehrstuhl fűr Stahlbau und Leichtmetallbau, Mies-van-der-Rohe-Str.1, 52074, Aachen, Germany

VTT Technical Research Centre of Finland Materials and Construction/ Indoor Climate and Building Services, PO Box 1000, 02044 VTT, Espoo, Finland

Centre Technique Industrial de la Construction Métallique (CTICM) Espace Technologique; Route de l'orme des merisiers, F-91193 Saint-Aubin, France

ArcelorMittal Research Liège Industry Centre Liège/ Steel Solution Design for Construction, PO Box 4000 Liège, Belgium

Corus Research, Development & Technology Swinden Technology Centre (STC), Moorgate, Rotherham South Yorkshire S60 3AR, United Kingdom Corus is now known as Tata Steel.

Beneficiaries:

PRz Politechnika Rzeszowska im. I. Lukasiewicza/Rzeszow University of Technology, W.Pola 2, 35-959 Rzeszow, Poland

Co-ordinator: Nancy Baddoo: The Steel Construction Institute

Authors: Mark Lawson, Nancy Baddoo & Guillaume Vannier (SCI); Bernd Doering & Markus Kuhnhenne (RWTH Aachen); Jyri Nieminen (VTT); Philippe Beguin & Stephane Herbin (CTICM); Giorgia Caroli (ArcelorMittal Research Liège); Israel Adetunji (Corus); Aleksander Kozlowski (PRz)

Commencement Date: 01 July 2007

Completion Date: 30 June 2010


Distribution List European Commission - DG RTD.G5

2 copies

TGS8 Committee Chairman: Mr Louis-Guy Cajot Arcelor Profil Luxembourg

TGS8 Committee Members:

Prof. Darko Beg Univ Ljubljana Slovenija

Mr Antonio Augusto Fernandes Univ Porto Portugal

Prof. Andrzej Klimpel Silesian University Of Technology Poland

Mr Anthony Karamanos A S Karamanos & Associates Greece

Mr Jouko Kouhi VTT Finland

Dipl.-Ing Hubert Lenger BEG Austria

Prof. Dr.-Ing. Gerhard Sedlacek RWTH Germany

Mr Adam Bannister Corus UK UK

Professor Joaquín Ordieres Mere Universidad de la Rioja Spain

Mr Thierry Braine-Bonnaire Arcelor France

Dr Ing Giuseppe Demofonti Centro Sviluppo Materiali Italy

Dr Walter Salvatore Univ Pisa Italy

Dr. Gerhard Knauf SZMF Germany


CONTENTS

Page No.

1 PROJECT OVERVIEW 7

2 FINAL SUMMARY 8

3 LIST OF DELIVERABLES 14

4 INTRODUCTION 17 4.1 Over-cladding of existing façades 17 4.2 Over-roofing or roof-top extensions 18 4.3 Modular units in renovation 19 4.4 Other European projects on renovation 20

5 WP1: RENOVATING COMMERCIAL AND RESIDENTIAL BUILDINGS: ENERGY EFFICIENCY STRATEGIES 21 5.1 Objectives 21 5.2 Recent experience of over-cladding 21 5.3 Investigation of steel intensive over-cladding systems 22 5.4 Design criteria for energy efficient over-cladding systems 23 5.5 Dimensional accuracy in over-cladding 25 5.6 Impact of air-tightness on energy demand 27 5.7 Study of the hygrothermal performance of an insulated over-cladding system 29

5.7.1 Description of over-cladding system 29 5.7.2 Indicators for performance and robustness of the system 30 5.7.3 Results 31

5.8 Analysis of thermal performance of double skin facades 32 5.9 Whole building thermal modelling of renovated buildings 33

5.9.1 Office building 33 5.9.2 Office building with roof-top extension 35 5.9.3 Apartment building 36

5.10 Innovative over-cladding systems incorporating energy creation 38 5.10.1 Field testing of thermal storage wall system 38 5.10.2 Field trials on transpired solar collectors as over-cladding 40

5.11 Design guidance on transpired solar collectors 46 5.11.1 Basic energy balance equations for TSC 46 5.11.2 Types of TSCs 47 5.11.3 Application of TSC to Over-Cladding Systems 48

5.12 Design guidance on renovating commercial/residential buildings 50 5.12.1 Over-cladding systems 50 5.12.2 Energy performance 51

6 WP2: RENOVATING INDUSTRIAL BUILDINGS: ENERGY EFFICIENCY STRATEGIES 53 6.1 Objectives 53 6.2 Problem areas in single storey buildings and examples of renovation 53 6.3 Analysis of cassette walls with improved thermal insulation 55 6.4 Strategy for achieving air-tightness in building renovation 57

6.4.1 Air leakage 57 6.4.2 Air leakage regulatory requirement 57 6.4.3 Poor air-tightness performance 58 6.4.4 Best practice guidelines for achieving air-tightness 58

6.5 Thermal building simulations - parametric study 59 6.5.1 Description of boundary conditions for the thermal analysis 59 6.5.2 Parameters for thermal analysis 60


6.5.3 Results of thermal analyses 61 6.6 Case studies on buildings before and after upgrading 62

6.6.1 Case Study 1: Potters Place, Skelmersdale, UK 62 6.6.2 Case Study 2: Milton Keynes, UK 67 6.6.3 Case Study 3: "L" assembly buildings, Poland 68 6.6.4 Case Study 4: Aircraft production hall, Poland 69 6.6.5 Case Study 5: Sports hall, Germany 70

6.7 Design guidance on over-roofing and over-cladding 71 6.7.1 Over-cladding of single storey buildings 72 6.7.2 Over- roofing of single storey buildings 72 6.7.3 Design requirements for over-roofing and over-cladding of single

storey buildings 73

7 WP3: STEEL INTENSIVE TECHNOLOGIES FOR BUILDING EXTENSIONS 74 7.1 Objectives 74 7.2 Review of recent experience 74 7.3 Investigation of buildability and technical issues 76 7.4 Connecting a vertical extension to an existing building 77

7.4.1 Steel column to concrete wall (point connection) 78 7.4.2 Pre-design study for steel portal frame connection to concrete wall 80 7.4.3 Light steel wall to concrete wall (continuous connection) 80

7.5 Safety and access issues 81 7.6 Investigation of semi-rigid corner joint characteristics 82

7.6.1 Test arrangement 82 7.6.2 Numerical simulations 83 7.6.3 Moment-rotation characteristics 83

7.7 Tests on the connection between a steel frame and existing concrete wall 84 7.7.1 Test arrangement 84 7.7.2 Test results 85 7.7.3 Tests on light steel wall panel with single boards 88

7.8 Design guidance for vertical extensions 89

8 WP4: LIGHT STEEL SYSTEMS TO UPGRADE ROOFS 90 8.1 Objectives 90 8.2 Investigation of buildability and practical aspects 90 8.3 Investigation of the Open Roof System 92

8.3.1 Introduction to the Open Roof System 92 8.3.2 Structural design of the Open Roof System 92

8.4 Simulation of thermal performance of upgraded roofs 95 8.4.1 Definition of simulation models for residential buildings 95 8.4.2 Simulation results for residential building 96

8.5 Evaluation of installation procedure for roof systems 98 8.6 Investigation of the application of innovative roofing systems in renovation 99

8.6.1 Steel roof integrated solar PV system 100 8.6.2 Standalone solar air heating system 100 8.6.3 Solar integrated ventilation heating system 101 8.6.4 Roof integrated solar water heat collector 101 8.6.5 Study of a photovoltaic system on a roof-top extension 103

8.7 Design guidance on roof-top extensions 103 8.7.1 Flat roof conversion 103 8.7.2 Pitched roofs conversion 103 8.7.3 Lightweight steel roof: “Open roof” 104 8.7.4 Dimensional planning for room in the roof space 104 8.7.5 Roof insulation and condensation 105 8.7.6 Fire safety 106


9 WP5: ECONOMIC AND SUSTAINABILITY JUSTIFICATION TOOLS & CASE STUDIES 107 9.1 Objectives 107 9.2 Economic justification software tool 107

9.2.1 Functional specification of tool 107 9.2.2 Parametric studies 108 9.2.3 Derivation of empirical relationships building energy demands 110 9.2.4 Implementation of software tool 111 9.2.5 Conclusions 113

9.3 Sustainability justification software tool 114 9.3.1 Derivation of relationship between U-value and embodied carbon 114 9.3.2 Development of tool 116 9.3.3 Demonstration of tool for Potters Place case study 117

9.4 Assessment of renovation in BREEAM and HQE 118 9.5 Case studies illustrating the technologies studied in this project 120

10 CONCLUSIONS 122

11 EXPLOITATION AND IMPACT OF THE RESEARCH RESULTS 123 11.1 Technical and economic potential 123 11.2 Dissemination of results 123

12 LIST OF FIGURES 124

13 LIST OF TABLES 127

14 LIST OF ACRONYMS AND ABBREVIATIONS 128

15 REFERENCES 129

APPENDIX A TECHNICAL ANNEX 131


ABSTRACT

ROBUST addresses the renovation and improvement of existing residential, industrial and commercial buildings using steel-based technologies, focusing on techniques such as over-cladding, over-roofing and roof-top extensions.

Steel-intensive renovation techniques currently on the market were reviewed. Performance criteria were developed for over-cladding systems meeting current regulatory standards, with guidelines on how to achieve appropriate levels of air-tightness.

Thermal simulations of single storey industrial buildings and multi-storey residential and commercial buildings before and after renovation were performed in order to determine the potential energy savings. The performance of a number of new over-cladding systems was studied numerically and also through laboratory tests.

The air-tightness and thermal performance of buildings in Poland, Germany and UK were measured before and after renovation. Field trials were carried out on over-cladding systems using large steel flat panels including a novel Transpired Solar Collector system.

Recommendations were developed regarding how a vertical light steel framed extension can be connected to an existing concrete building and load tests were carried out on different systems.

The potential for light steel systems to provide new habitable space by renovating existing timber roofs was studied. Various systems incorporating energy creation schemes were investigated.

The thermal simulation data were used to develop a simplified tool for assessing the economic viability of alternative steel intensive renovation solutions. A simplified tool for comparing the embodied carbon of different renovation systems was also developed. A series of Case Studies was prepared to illustrate the practical use of these renovation technologies.


1 PROJECT OVERVIEW

CATEGORY OF RESEARCH Steel

TECHNICAL GROUP: TGS8

REFERENCE PERIOD: 1 July 07 to 30 June 10

GRANT AGREEMENT N°: RFSR-CT-02007-00043

TITLE: RENOVATION OF BUILDINGS USING STEEL TECHNOLOGIES (ROBUST)

BENEFICIARIES:

The Steel Construction Institute (SCI), UK RWTH Aachen, Germany VTT Technical Research Centre of Finland CTICM, France Arcelor Research Liège, Belgium Corus, UK PRz, Poland

COMMENCEMENT DATE: 1 July 07

COMPLETION DATE: 30 June 10

WORK UNDERTAKEN: See Sections 5 to 9.

MAIN RESULTS: See Sections 5 to 9.

FUTURE WORK TO BE UNDERTAKEN:

The project is complete. All objectives foreseen have been achieved.

ON SCHEDULE (YES /NO): Complete

PROBLEMS ENCOUNTERED:

Some delays occurred to some WPs during the project but everything has now been completed and is reported herein.

CORRECTION – ACTIONS It was possible to accommodate deviations in the finalisation date of some deliverables within the overlal timeframe of the project.

PUBLICATIONS - PATENTS None

BUDGET INFORMATION PER BENEFICIARY

Beneficiary Total amount spent to date (€) Total allowable cost € as foreseen in Grant Agreement

SCI 385,531 279,994

RWTH Aachen 248,652 244,056

VTT 114,420 119,312

CTICM 190,724 177,000

Arcelor Research Liege 258,011 181,223

Corus 199,497 197,463

PRZ 81,490 87,459

TOTAL 1,478,324 1,286,507


2 FINAL SUMMARY

Project objectives

The objective of this project was to study the use of steel technologies in the renovation, adaptation and upgrading of existing buildings in all sectors. It addressed the following key aspects:

Strategies to improve thermal efficiency and to arrest deterioration of existing concrete and masonry facades in housing and residential buildings, for example by over-cladding.

Strategies to improve thermal efficiency and air-tightness of roofs and walls of industrial buildings, for example by over-cladding or re-cladding.

Building extensions and conversions using steel-intensive and prefabricated technologies, including new floors and roofs.

Retrofit of timber roofs in housing by steel systems.

Economic assessment of building improvements and energy saving against construction cost, including case studies of recent projects.

WP1 Energy efficiency strategies – residential & commercial buildings

This work package addressed ways in which the thermal performance of commercial and residential buildings may be improved by over-cladding.

1) Investigation of steel intensive over-cladding systems

A review of recent experience of over-cladding projects using steel in Belgium, Netherlands, UK, Finland, Italy, France, Denmark and Germany was prepared. The main drivers for renovation, with specific opportunities for steel, were identified during this review. Key design criteria for over-cladding systems were developed, covering air-tightness, thermal insulation, design life, wind loading, etc. A series of techniques to ensure appropriate levels of air-tightness in over-clad buildings were recommended.

2) Study of the hygrothermal performance of an insulated over-cladding system

A hygrothermal (i.e. humidity and temperature) analysis of an over-cladding system subject to varying outdoor climate data, solar and long wave radiation, wind and driving rain was carried out based on dynamic heat and moisture calculations. Generally, the system demonstrated good performance in all climates, independent of the insulation thickness. The performance of the system did not seem to be significantly affected by the presence of slight or no ventilation of the cavity between the old and new structure or moderate water intake from driving rain.

3) Whole building thermal modelling before and after renovation

Thermal simulations were carried out on a model of a 4 storey office building. Annual space heating and cooling demand for each climate were calculated as total demand (MWh) and specific demand (kWh/m2 gross floor area). The study showed that improved thermal insulation of an office building resulted in decreased space heating demand, but increased cooling demand. Hence designing a renovation system for a building with high internal heat gains needs to be carried out in a holistic way, considering the whole building as a system.

Two similar investigations were carried out for apartment buildings. One was for a four storey building, consisting of a basement and three upper storeys. The second study was for a ten storey apartment which involved a parametric analysis varying climate, building dimensions, percentage glazing, U-values (façade and roof), air-tightness and the addition of a roof-top extension. The output of this study was used to develop empirical expressions for energy demand in the economic justification tool.


4) Field tests on transpired solar collectors in over-cladding

Field tests were carried out on the practical use of a novel Transpired Solar Collector (TSC), which is a variant of the Solarwall™ system, for the over-cladding of existing concrete or masonry buildings. A TSC comprises a perforated external metal sheet which is heated by solar irradiation, and external air is aspired through this perforated sheet and pre-heated on its way through the cavity. The heated air is actively brought into the building to provide ventilation space heating.

The tests were carried out on a tower block at Oxford Brookes University in the UK, which is now disused but is still serviced The south facing façade was over-clad on the lower two levels and this was extended onto the east facing facade. The metallic panels were manufactured from grey colour-coated steel, with up to 2,500 perforations per m2. Two of the panels between the windows in each floor level were perforated and the other panels were unperforated. The weather conditions, temperatures and air flow were measured regularly. For a 10C temperature difference between incoming air and the internal air, a 5 hour heating period, an air-flow rate of 60 litres/sec, 5.3m2 area of TSC panels (per floor) and assuming 150 days per year have this level of solar radiance, the heat generated by the TSC was estimated to be 540 kWh. Assuming this heating energy is distributed over a building width of 5 m and length of 10 m, the energy provided by the TSC is 11 kWh/m2 floor area. This is equivalent to about 10% of the heating demand of the over-clad building. The energy required to operate the fan is equivalent to about 7% of the heating energy that is created.

5) Field testing of thermal storage wall system

Field trials were carried out on the use of a thermal storage system in thermally massive walls to see if it is possible to increase solar gain during cold periods and to stabilize the interior temperature in hot periods. A thermal storage wall was constructed using a light steel frame, designed both for south-facing elevations of new buildings and for the extension of existing structures with a southerly aspect. Measurements were carried out in a climatic chamber with the internal temperature maintained at about 20C, for thermal comfort of occupants. A black sheet steel on the south-facing glazing acted as an absorber which quickly reacted to changes in temperature, making the absorber work even during short periods of intense solar heat. The thermal storage wall accumulated thermal energy and transmitted it to the interior, thus significantly reducing the consumption of energy. The delay in heat transmission is advantageous in summer as it prevents interiors from overheating. Thermal comfort is also enhanced by heat insulating roller blinds, which reduce the temperature during summer days and limits heat losses during winter nights. Numerical analyses were carried out to optimise the performance of the thermal storage wall with reference to its configuration and the materials used.

WP2 Energy efficiency strategies – industrial buildings

This work package addressed ways in which the thermal performance of industrial buildings may be improved by over-cladding, re-cladding and over-roofing.

1) Analysis of cassette walls with improved thermal insulation

Detailed information on the thermal performance of industrial buildings was collected in order to identify weak points in existing forms of construction. To illustrate the thermal problems that may be encountered, infra-red (IR) surveys were carried out on a number of typical buildings.The IR surveys of industrial buildings in lightweight steel construction demonstrate that cassette walls can have poor thermal performance. Laboratory tests in a hot box supported this finding. New solutions with improved thermal quality were investigated, including re-cladding using additional insulation or over-cladding using steel-sandwich elements. The re-cladding solution was studied in detail using finite element analysis and hot box tests. The studies showed that the U-value of the façade can be improved from about 0.8 W/m²K for the simple cassette wall (100 mm deep) to 0.24 W/m²K by using a sandwich element of 120 mm depth and thermal conductivity of 0.045 W/mK.

2) Strategy for achieving air-tightness in industrial building renovation

With increasingly stringent building regulations, envelope air-tightness is a critical element of low energy design. A review of air-tightness in industrial buildings was carried out, including a comparison of regulatory requirements in Europe. Air-tightness data from physical tests on different types of


buildings were analysed. The reasons for poor air-tightness performance were identified at the pre-design, design and construction stages and a strategy proposed for how to achieve better air-tightness performance.

3) Thermal building simulations - parametric study

Thermal building simulations were carried out to estimate heating demand data for a wide range of building scenarios in order to derive empirical relationships for energy demands before and after renovation (‘good’, ‘better’ and ‘best’ practice). The empirical relationships for heating demand were implemented in the economic justification tool developed in Section 9. A total of 216 analyses were carried out.

It can be deduced from the results that building orientation and roof lights percentage (12% and 20%) have very little impact on the total annual heating demands for the three locations studied. However, the impact of orientation and roof lights percentage would be higher if over-heating and cooling demand were considered in the analysis. Overall, the result highlighted that considerable energy savings can be made when buildings are renovated. Whereas, the ‘best’ practice renovation option provided the highest energy savings, the decision regarding the level and scope of renovation largely depends on the drivers for renovation, such as national regulatory requirements and acceptable level of return on investment in different countries.

4) Case studies on buildings before and after renovation

Air-tightness and thermography tests were carried out on a number of existing buildings before and after improvements to their building envelope. For an industrial building in Skelmersdale, UK, the measured values were compared with values predicted by the UK Simplified Building Energy Model.

WP3 Steel intensive technologies for extensions & conversions

This work package addressed ways in which buildings may be extended to create new habitable space, including use of prefabricated steel technologies.

1) Design issues relating to constructing a vertical light steel framed extension

A study was carried out to collect information for European countries on the most common dimensions of residential buildings and the essential regulatory requirements covering structural design, fire safety, thermal performance etc. A case study based on a vertical extension project involving two types of roof was analysed in detail. Key points throughout the building were identified as potentially critical with respect to requiring special interface requirements.

Various design solutions for the connections between a vertical steel extension and an existing concrete building were developed for both point and continuous connections. Safety and access issues were also discussed.

2) Investigation of semi-rigid corner joint characteristics

A study was carried out to determine the semi-rigid corner joint characteristics of a bolted lap joint in a thin walled portal steel frame for use as a vertical extension. Laboratory tests were carried out to calibrate a numerical model which was then used to generate moment-rotation curves for the joint.


3) Tests on the connection between a vertical steel frame extension and existing concrete wall

A series of load tests on steel frames connected to concrete parapet walls also showed the load carrying capacity of the support to these frames in building extensions. Horizontal loads of 50 kN per concrete support were resisted by 4 bolted connections, which is over two times higher than the horizontal wind forces on a 3m high single storey extension with supports at 6 m spacing .

Tests were also carried out on light steel wall panels subject to shear. The main objective was to obtain semi-rigid characteristics of the panel under horizontal loading and to estimate the stiffness of the panel, which is needed for a global analysis of the structure.

WP4 Use of light steel systems to upgrade roofs

The purpose of this work package was to investigate the ways in which timber roofs can be renovated using steel technologies to provide better use of the roof space and to improve the thermal performance of roofs.

1) Review of current roof conversion systems

Current roof typologies, roof structural arrangements and refurbishment practices in Europe were reviewed. A generic conversion methodology to create habitable roof space was developed and opportunities for light steel solutions were highlighted.

2) Study of Open Roof System

An innovative renovation system for timber roofs called the Open Roof System was studied. One form of the system uses steel and plywood compositely to create a ‘plyweb’ beam for modification of existing roof structures to create an habitable roof. The second form involves the use of cold-formed C or Z sections to create a room-in-the roof truss. A trial design of an 8 m Open Roof truss in accordance with Eurocode 3 was carried out. The design is based on a modified plastic analysis. The deflections and internal forces were predicted from a finite element analysis.

3) Simulation of thermal performance of upgraded roofs

Thermal simulations were performed for a detached bungalow, mid-terrace house, semi-detached house and detached house in order to illustrate the energy savings that can be achieved by renovation. The following issues were taken into account in the analyses:

U-value of the construction before/after renovation (including control of thermal bridges)

Increasing compactness (additional floor space with only few additional surfaces of building envelope)

Control of over-heating (large surfaces exposed to solar irradiation combined with little mass)

Air permeability (difficulty in quantifying air permeability of the old and new roof structure)

The results show that the combination of additional space and retrofit of the existing building leads to a high energy saving potential.

4) Evaluation of installation procedure for roof systems

A series of projects using the Corus prefabricated Hi-point roof system were studied. Hi-point is an advanced modular roofing system using lightweight cold-formed steel sections which is suitable for renovation and new-build projects.

5) Renovation roofing systems with energy creation systems

Innovative roofing systems which include energy generation systems are described. Laboratory tests were carried out using a hot box on a prototype roof-integrated solar water heat collector system. The principle of the system is that solar energy heats up water which circulates in tubes embedded in the external surface of the thermal insulation. The efficiency of the system was measured for varying mass


flow rates of water and temperature. A parametric study of PV arrays on the roof of a vertical extension was also carried out to evaluate the potential for energy generation.

WP5 Justification tools and case studies

The purpose of this work package was to develop two simple pre-design tools, one covering the economic justification of renovation and one covering sustainability justification aspects. Case studies were also prepared featuring buildings around Europe.

1) Economic justification tool

A multi-criteria spreadsheet tool was developed to support developers’ decisions regarding whether to demolish or renovate a building. The tool estimates the potential cost savings arising from over-cladding and/or over-roofing and/or constructing a roof-top extension using steel technologies. It includes issues such as savings in heating bills, reduced maintenance costs, improved visual aspects, increased rental value and the benefit of a longer building life. National variations in certain parameters are taken into account. It covers rectangular, multi-storey residential and commercial buildings and single storey industrial buildings.

The tool gives two methods for the calculation of the energy savings:

A simplified method whereby the energy savings are estimated by the tool itself based on empirical relationships derived from parametric studies on thermal analyses of different building types

A direct input method whereby the user can input the results from a more detailed energy calculation using a third party thermal simulation software.

The tool calculates the payback period using a net present value calculation.

2) Sustainability justification tool

A simple spreadsheet tool was developed which estimated the embodied carbon of a range of renovation solutions for industrial, commercial and residential buildings. An LCA (Life cycle assessment) was carried out for ten renovation solutions in order to develop an algorithm for describing the empirical relationship between the U-value (thermal transmittance) of each renovation option and associated embodied carbon emission CO2/m

2. The LCA was based on material bills of quantities. From these data sets, empirical relationships between embodied carbon emissions and U-values were developed.

The tool demonstrated that the embodied carbon emissions of composite over-cladding panels are higher than for built up systems because the carbon content of PUR/PIR foam insulation is higher than mineral wool insulation. The tool also shows that as the thermal performance of the envelope improves, the embodied carbon emission increases. This is largely due to the increase in insulation thickness to achieve the lower U-values. This highlights the fact that, as the building becomes more energy efficient and operational energy decreases, the embodied energy considerably increases as a proportion of the whole lifecycle emissions of the building. Nonetheless, the overall carbon emission of low energy buildings or buildings refurbished to current thermal regulatory requirement is much lower than those of buildings built before modern thermal regulations.

3) Case studies

The following eleven case studies of European buildings which have undergone renovation were prepared:

1) Over-cladding using built up system in Milton Keynes, UK

2) Renovation of office building in Milan, Italy

3) Roof-top extension of residential building in Rotterdam, The Netherlands

4) Renovation of commercial building in Milan, Italy

5) Over-cladding of industrial shed using SolarWall™ system, Co. Durham, UK


6) Renovation of commercial building in Paris, France

7) Roof-top extension of university building in Rzeszow, Poland

8) Roof-top extension of residential building in Boulogne, France

9) Roof-top extension in Saint Ouen, France

10) Over-cladding of industrial building using composite panels, Scotland

11) Renovation of residential building in East London, UK


3 LIST OF DELIVERABLES

All deliverables have been uploaded onto a publicly-accessible web site dedicated to this project: www.steel-renovation.org

Figure 3.1 Homepage of ROBUST project site

The deliverables comprise:

56 individual activity reports which describe the work completed for the tasks under each Work Package,

11 case studies of different types of renovation projects across Europe,

Two spreadsheet tools, one which calculates the economic justification of steel renovation systems and one which calculates the sustainability justification of steel renovation systems.


Title Author

WP1 Energy efficiency strategies – residential & commercial buildings

WP 1.1.1 European case studies on over-cladding SCI

WP 1.1.2 Drivers for renovation in various sectors SCI

WP 1.1.3 As built building typology and performance ArcelorMittal

WP 1.1.4 Survey of buildings using laser scanning OBU

WP 1.2.1 Investigation of over-cladding systems and attachment strategies ArcelorMittal

WP 1.2.2 Generic forms of over-cladding systems SCI

WP 1.2.3 Over-cladding visualisation studies OBU

WP 1.3.1 Improving air-tightness in over-cladding and over-roofing ArcelorMittal

WP 1.3.2 Strategies to improve air-tightness in building renovation SCI

WP 1.4.1 Analysis of thermal performance of double skin facades ArcelorMittal

WP 1.4.2 Hygrothermal performance of over-cladding solutions VTT

WP 1.5.1 Study of energy performance of over-clad buildings VTT

WP 1.5.2 Thermal analysis of office building - heating demand RWTH

WP 1.5.3 Thermal analysis of office building - cooling demand RWTH

WP 1.6.1 and 1.7 Field tests on thermal storage wall system PRz

WP 1.6.2 and 1.7 Field tests on an over-cladding Transpired Solar Collector renovation system SCI

WP 1.7 Review of innovative cladding systems RWTH

WP 1.8.1 Design guidance on renovating commercial and residential buildings VTT

WP 1.8.2 Design guidance on Transpired Solar Collectors in renovation SCI

WP2 Energy efficiency strategies –industrial buildings

WP 2.1 Review of recent experience renovating industrial buildings in Germany RWTH

WP 2.2.1 Detailed analysis of improved thermal insulation RWTH

WP 2.2.2 Solutions for over-cladding and re-cladding RWTH

WP 2.2.3 Strategies for achieving air-tightness in industrial buildings Corus

WP 2.3.1 Thermal simulations - evaluation of key parameters on energy demand Corus

WP 2.3.2 Thermal simulations study of industrial sheds Corus

WP 2.4.1 Air pressurisation tests before renovation for Potters Place Corus

WP 2.4.2 Smoke propagation test and thermography survey for Potters Place Corus

WP 2.4.3 Air tightness and smoke propagation test for Milton Keynes industrial sheds Corus

WP 2.4.4 Physical tests before and after upgrading - roofs and facades in Poland PRz

WP 2.6 Design guidance on energy efficiency strategies in industrial buildings RWTH

WP3 Steel intensive technologies for extensions & conversions

WP 3.1.1 Review of building renovation using light steel framing SCI

WP 3.1.2 Review of modular construction in renovation SCI

WP 3.1.3 Review of roof-top extensions using light steel construction SCI

WP 3.2.1 Design of two connection systems for light steel vertical extensions ArcelorMittal

WP 3.2.2 Vertical and horizontal extensions - problems, techniques and recent examples ArcelorMittal


WP 3.2.3 Experimental studies of bolted lap joint in cold-formed steel frame PRz

WP 3.3.1 Design study for connection systems for a vertical steel extension CTICM

WP 3.3.2 Test specification - connection system for a vertical steel extension CTICM

WP 3.3.3 Experimental studies of attachment of new floors, roofs and building extensions PRz

WP 3.4 Design guidance for extensions CTICM

WP4 Use of light steel systems to upgrade roofs in residential and commercial buildings

WP 4.1.1 and 4.2 Review of recent European roof upgrades Corus

WP 4.1.2 Roof typology, structural arrangement and opportunities for steel for habitable roofs Corus

WP 4.2.1 Investigation of buildability and practical aspects of upgrading existing roofs Corus

WP 4.2.2 Renovation of Roofs using Open Trusses in Light Steel C Sections SCI

WP 4.2.3 and 4.3 Review of roof typologies and specification for thermal analysis Corus

WP 4.3 Thermal simulations of upgraded roofs RWTH

WP 4.4 Site trials on practical roof system Corus

WP 4.5.1 Performance of facade and roof integrated solar collector VTT

WP 4.5.2 Integration of energy creation systems into upgraded roofs RWTH

WP 4.5.3 Study of photovoltaic system on a rooftop extension CTICM

WP 4.6 Design guidance on light steel systems for upgrading roofs Corus

WP5 Justification tools and case studies

WP 5.1.1 Building energy simulation results for residential building OBU

WP 5.1.2 Development of economic justification tool for renovation SCI

WP 5.1.3 Economic justification tool SCI

WP 5.1.4 and 5.2 Economic and sustainability aspects of renovation in steel CTICM

WP 5.2.1 Review of renovation solutions Corus

WP 5.2.2 Development of embodied carbon calculator for refurbishment Corus

WP 5.2.3 Embodied carbon calculator Corus

WP 5.3.1 Over-cladding using built up system in Milton Keynes Corus

WP 5.3.2 Renovation of 60s Building in Milan ArcelorMittal

WP 5.3.3 Roof-top extension of residential building in Rotterdam SCI

WP 5.3.4 Renovation of commercial building in Milan ArcelorMittal

WP 5.3.5 Over-Cladding using Solar Wall in County Durham Corus

WP 5.3.6 Renovation of commercial building in Paris CTICM

WP 5.3.7 Roof-top extension of university building in Poland PRz

WP 5.3.8 Roof-top extension of residential building in Boulogne CTICM

WP 5.3.9 Roof-top extension in Saint Ouen CTICM

WP 5.3.10 Roof over-cladding using composite panels in Scotland Corus

WP 5.3.11 Renovation of residential building in East London SCI


4 INTRODUCTION

Renovation, repair and maintenance of buildings accounts for 40% of all expenditure in the building construction sector across Europe. It is important for social, economic and sustainability viewpoints that the existing building stock is brought up to modern standards in terms of comfort, functionality and energy performance. In many countries, a high proportion of existing buildings (and especially houses) were constructed before modern regulations. New buildings account for only 1% of the existing stock and therefore the greatest improvements in terms of energy saving and comfort can be made by addressing the renovation and upgrading of these buildings, rather than by new building.

In inner city areas, planning and conservation requirements mean that it is necessary to retain the existing street-scape rather than to re-build, and therefore technologies to extend and adapt buildings to new uses must be sympathetic to the existing form and ways of working in urban areas. Extending or modifying buildings often involves use of steel technologies, but there are particular problems that should be addressed in terms of the construction process, and optimum use of prefabricated systems, interfaces with the existing parts of the building and issues such as safety, stability and loading. An ECSC demonstration project [1] completed in 2003 showed how modules could be used efficiently in roof-top extensions to existing buildings and has led to new markets.

This project studies the use of steel technologies in the renovation, adaptation and upgrading of existing buildings in all sectors, addressing the following key aspects:

Over-cladding of existing masonry facades in housing and residential buildings, to improve thermal efficiency and to arrest deterioration.

Over-cladding or re-cladding of roofs and walls of industrial buildings to improve thermal efficiency and air-tightness.

Building extensions and conversions using steel-intensive and prefabricated technologies, including new floors and roofs.

Retrofit of timber roofs in housing by steel ‘open’ roof systems.

An economic assessment of building improvements and energy saving against construction cost, including case studies of recent projects.

The work scope also takes into account national differences in building practice, and also climatic and economic factors. The project will lead to greater opportunities for development of steel-intensive technologies specifically for the renovation sector, by pre-competitive research aimed at understanding the key building physics, buildability and economic factors that are relevant to this sector.

4.1 Over-cladding of existing façades Over-cladding is defined as the attachment of new cladding directly over an existing façade [2], and is differentiated from ‘re-cladding’ in which the existing cladding is replaced. Over-cladding is carried out in order to:

Reduce the heat losses through the façade and to meet modern thermal regulations.

Improve the appearance of the building.

Arrest the deterioration of the existing structure or façade, including water leakage.

Minimise disruption to the occupants during the renovation process.

Over-cladding can use a variety of materials, including composite (or sandwich) panels or metallic cassette panels, as shown in Figure 4.1. Insulation is provided behind the new cladding and may be attached to the existing wall with suitable weather protection.


Over-cladding often involves use of a sub-frame which is attached either directly to the existing façade, or preferably to the existing floors or primary structure which avoids attachment to a potentially weak existing façade material. Storey high sub-frames can be created and their attachments require some form of adjustment for site tolerances, and also to account for the irregularity of the existing façade.

Many residential, commercial and educational buildings have been over-clad, particularly in the UK and in Scandinavia using a variety of metallic cladding systems. Often over-cladding is combined with over-roofing as part of a comprehensive renovation strategy. New windows are also provided so that the overall savings in energy use are dramatically reduced.

The in-service performance of over-cladding systems is strongly affected by the need to provide considerable improvements in thermal performance and to prevent water ingress whilst allowing the moisture with in the building or existing façade to egress.

Figure 4.1 Examples of over-cladding of concrete panel buildings using horizontally orientated metallic panels

4.2 Over-roofing or roof-top extensions ‘Over-roofing’ is a terms used for the creation of a new roof structure to an existing building [3,4]. The main reasons for over-roofing are the poor performance of the existing roof (such as water leakage) and the desire to utilize the space in the roof, for example, for communal use or as new apartments. The form of the new roof construction depends largely on whether or not the space is intended for habitable use. The value of the new space created can pay for all the renovation work. Light steel framing may be used in ‘over-roofing’ schemes in the following forms:

Closely spaced trusses spanning between façade walls.

Widely spaced trusses spanning between façade walls and supporting purlins spanning between them.

Portal frames or other moment-resisting structures supported on perimeter columns.

Lightweight steel structure supported by a grillage of steel beams that are supported at discrete locations such as columns below.


The trusses may take the form of simple pitched trusses (normally ‘Fink’ or ‘Pratt’ trusses) or mansard-type trusses, creating deeper useable space. In terms of roof-top extensions, a light steel super-structure supported on steel beams spanning over the existing flat or slightly pitched roof is often the optimum solution, as shown in Figure 4.2.

Figure 4.2 Two storey extension of an existing building using light steel framing, Rotterdam

4.3 Modular units in renovation Buildings may be extended easily using modular or ‘volumetric’ units which are self-supporting vertically, but which are supported laterally by the existing structure. Modules are generally less than 3.6 m wide so that they can be transported without special escort and are easily lifted into place. Cladding can be pre-attached, or can be installed conventionally on site. The use of modular units in renovation applications is most well established in Scandinavia. Interest in modular construction for building extensions is increasing in the UK, and recent applications include medium-sized hotels and social housing projects.

Figure 4.3 Roof-top extension using modules at Plymouth University, UK


4.4 Other European projects on renovation Issues relating to the renovation of buildings are being investigated in a number of European research projects, although none of them focus on steel technologies. Five of these projects are summarised briefly below:

STACCATO (Sustainable Technologies And Combined Community Approaches Take Off)

This is a Sixth Framework Project. The main objective of the project was to accelerate the implementation of renewable energy and efficiency measures in the redevelopment of large areas. Three ambitious demonstration sites (2500 apartments) are being constructed and monitored. Research on the technical and socio-economic aspects will result in wider applicable technical concepts and approaches for parties to start new renovation projects.

Annex 50 Prefabricated Systems for Low Energy / High Comfort Building Renewal

The International Energy Agency is running this project under its Energy Conservation in Buildings and Community Systems Programme. The project started in January 2007 and finished in 2010. The objectives were the development and demonstration of an innovative whole building renovation concept for typical apartment buildings based on prototype, prefabricated roof systems with integrated HVAC, hot water and solar systems and highly insulated envelopes with integrated new distribution systems for heating, cooling and ventilation. Although not material specific, there were some shared objectives with ROBUST and a meeting with the Annex 50 partner EMPA was held to discuss tools for predicting the cost of renovation.

FC-DISTRICT

The overall objective of the FC-DISTRICT project is to optimize and implement an innovative energy production and distribution concept for sustainable and energy efficient refurbished and/or new districts. The concept is based on dynamic heat exchange between the building(s) (fitted with Solid Oxide Fuel Cells (SOFCs) for energy production collaborating with improved thermal storage and insulation building systems), the distribution system (optimized piping and district heating with or without a heat buffer) and the consumer (new business and service models), aiming to achieve energy balance at district level. Advanced insulation materials will be developed and implemented for the improvement of building and pipe thermal response. The project started in 2010 and is due for completion in 2014.

REDUCA

The aim of the programme is to ensure that buildings have optimum interior quality and increased energy efficiency. The project is co-financed by the European Regional Development Fund (ERDF), part of the ‘Technical Assistance’ Operational Programme 2007-2013, and backed primarily by Acciona. The main goal of REDUCA requires the development of new technologies designed to be applied in the renovation of school buildings in Andalusia. The project started in 2007 and is due for completion in 2013.

BEEM-UP

The BEEM-UP project (Building Energy Efficiency for Massive market UPtake) will demonstrate the economic, social and technical feasibility of retrofitting initiatives for reducing the energy consumption in existing buildings, and lay the groundwork for market uptake. The aim is to develop and demonstrate cost-effective and high performance renovations of existing residential multi-family buildings, significantly reducing the energy consumption. The project started in 2011 and is due for completion in 2014.


5 WP1: RENOVATING COMMERCIAL AND RESIDENTIAL BUILDINGS: ENERGY EFFICIENCY STRATEGIES

The activity reports relating to this Work Package are available at www.steel-renovation.org.

5.1 Objectives This Work Package addressed the ways in which the physical and thermal performance of existing housing, apartment buildings and commercial buildings may be improved. It concentrated on larger buildings in which steel-intensive cladding systems are more acceptable and examined the technological issues that should be solved in order to:

Increase the thermal performance by externally attached insulation and metallic facades of various types, including the environmental conditions behind the new cladding and the influence of air and moisture movement.

Reduce the water penetration and deterioration of the existing building, based on measurements of performance.

Demonstrate the increased design life performance provided by the new façade after renovation by numerical modelling, laboratory tests and physical tests on real buildings.

Examine opportunities for pre-fabrication of large over-cladding panels using light steel sub-frames.

Investigate buildability assessments of the construction processes for various building forms

5.2 Recent experience of over-cladding It is estimated that there are 200-250,000 concrete panel buildings in the European Union which were constructed between the 1950s-80s, of which at least 10% are in urgent need of renovation, and potentially a much higher percentage in Eastern Europe.

A review of recent experience of over-cladding projects using steel in Belgium, Netherlands, UK, Finland, Italy, France, Denmark and Germany was prepared. Key drivers for renovation, with opportunities for steel, were identified during this review and are given in Table 5.1.


Table 5.1 Key drivers for renovation of buildings

Key Drivers Opportunities for steel

Commercial Buildings

Improvement in external appearance for business-letting reasons, i.e. to increase rental value

Re-cladding of commercial buildings rather than over-cladding is preferred, often using highly glazed facades with external steelwork.

Re-servicing to suit modern usage including IT, HVAC, etc.

Reinforced concrete frames are inflexible for re-servicing and parts may be demolished and replaced by steel structures e.g. Slimdek. Light steel infill walls replace existing heavy weight walls to save weight and space.

Building extensions (often vertical) to add value to the building

Opportunities for primary steel frames and light steel infill walls in building extensions

Retention of existing Victorian/Edwardian facades and construction of new structure internally

Steel frames are used internally (often long span cellular beams). Minimum floor-floor height can lead to use of Slimdek. Existing widely used technique which favours use of steel as the support structure

Residential Buildings

Improvement of existing buildings to meet national regulations regarding energy efficiency

Few opportunities in renovation of existing housing, except as noted below.

Upgrading of deteriorating facades of concrete panel buildings built between the 1950s-80s

More opportunities for steel in over-cladding, new balconies etc in multi-storey apartments, especially RSL (Registered Social Landlord) owned

Non-cavity low-rise housing units (pre 1930) need improvements in energy efficiency

Opportunity for over-cladding of older housing using thin wall technology.

Roof-top extensions to create new rooms or apartments is financially beneficial

Opportunities for light steel framing and modular construction in roof-top extensions.

Roof cladding (re-roofing) Existing market which favours steel and lightweight cladding e.g. highly insulating composite panels and Kalzip.

5.3 Investigation of steel intensive over-cladding systems The forms of over-cladding currently in use in Europe were analysed and are described generically as follows:

1. ‘Rain-screen’ cladding, in which gaps between the external cladding panels provide for ‘pressure equalisation’ to minimize ingress of wind-driven rain [5]. The new insulation is fixed to the existing façade, as any insulation in the new cladding layer is largely ineffective due to the air movement behind. Protective strips are required to prevent rain penetration at the joints in the rain-screen panels. Additional vertical and horizontal barriers are also required periodically to provide rapid pressure equalisation that is fundamental to the rain-screen principle.

2. Drained and ventilated cladding permits any water that enters behind the new cladding to be drained and expelled. The joints between the cladding panels are narrower than in rain-screen systems, but otherwise they are similar. As for rain-screen systems, insulation is attached to the existing façade. Effective ventilation allows for rapid drying out of any moisture that remains in the cavity behind the new cladding.

3. ‘Face sealed’ cladding provides a watertight barrier, which is similar to new cladding. In this case, the cladding is insulated and sealed, and the possibility of vapour movement is minimal except for vertically to roof level. This system is less likely to be used if the existing façade is vapour permeable, as moisture may be trapped. Controlled ventilation can be provided in otherwise ‘face-sealed’ systems by special plastic ventilators, or in a controlled manner through the joints between the cladding panels. The amount of ventilation is small and is sufficient to control condensation but does not significantly affect the insulation provided by the over-cladding panels. ‘Trickle’ or uncontrolled ventilation can also be provided in otherwise ‘face-sealed’ systems at the


joints between the cladding panels. The amount of ventilation is uncontrolled as it relies on buoyancy and pressure effects. However, it is sufficient to control condensation but may affect the insulation provided by the over-cladding panels

4. ‘Directly’ attached cladding, such as insulated render, has no gap between the new and existing cladding. The insulation (normally mineral wool) is attached to the façade and directly rendered. Some ventilation facility may be required to prevent build-up of moisture behind the insulated render. This system is widely used for over-cladding low-rise buildings.

If the quality of the existing façade is poor, and therefore fixings to it may not be reliable, a sub-frame may be required to span between floor slabs or columns.The depth of the sub-frame should be minimized so that it does not increase the thickness of the over-cladding system that is used. Also, it may influence ‘cold bridging’ in which the sub-frame or its attachments pass through the new insulating layer.

The sub-frame may be of various generic forms:

Vertical rails (normally C sections) at approximately 600 mm centres to which the new cladding is fixed. These rails may be directly fixed to the existing cladding, as shown in Figure 5.2(a), or may span between the floor slabs, as shown in Figure 5.2(b). Direct fixing to the cladding may use L shaped sections with fixings at 0.6 to 1 m spacing vertically. Free spanning systems may use C or Z sections with sufficient bending stiffness to resist wind loads over a 2.7 to 3.2 m span.

A combination of vertical and horizontal rails in the form of a sub-frame which spans between floors or columns, and provides for attachment of the new façade and window frames. This system is illustrated in Figure 5.2(c). The horizontal members in the sub-frame may consist of single or double C sections depending on the spacing of the attachment points. Ideally, the fixing points are made to the strong points in the existing structure and should be arranged so that failure of one fixing allows its applied force to be transferred to the adjacent fixings.

Horizontal rails which support long spanning panels at each floor level. Figure 5.2(d) shows a horizontal rail in the form of a modified C section supporting vertically spanning composite panels. Trickle ventilation is provided at the horizontal joints in the panels.

Highly perforated steel profiles reduce cold bridging and may be used in all the sub-frames. However, local heat loss still occurs at points of attachment. Steel members are more compact than aluminium members, and are preferred for long span (2.7 – 3.2 m) applications.

An architectural representation of a typical over-clad building using large steel horizontally orientated cassette panels, is shown in Figure 5.1. The studies are based on a ‘live’ project (the redevelopment of buildings on the Gipsy Lane Campus of Oxford Brookes University).

5.4 Design criteria for energy efficient over-cladding systems A renovation system should:

Be weather-tight (in a lot of cases the existing façade is not weather-tight anymore).

Support its own weight.

Resist wind loads.

Increase thermal insulation and air-tightness.

Have a long life span.

Fulfil fire regulations.

Compensate for the unevenness of the existing walls, via the use of special profiles.


Figure 5.1 Representation of over-clad building using large steel cassette panels

Continuous L section

Mineral woolinsulation

New cladding(steel panel)

Existing facade

Sheathing board to support newcladding

Steel angle with 2 fixings to slab

Mineral wool insulation

Existing floor slab

Light steel frame

Slotted hole

(a) Continuous attachment of L-sections to the existing facade (b) Individual vertically spanning C sections attached at floor levels

Light steel frame

Sheathing board to support newcladding


Mineral wool insulation

Existing floor slab

Slotted hole

Existing floor slab

Composite panel


Horizontal rail(150 x 70 x 2)

Joint in composite panel

(c) Light steel sub-frame spanning between floor and attached at strong points

(d) Horizontal rails and vertically spanning cladding panels, such as composite panels

Figure 5.2 Various forms of light steel sub frames in over-cladding systems


A new over-cladding system would generally be designed to satisfy the thermal performance requirements of new buildings to National Codes. A target U-value of 0.17 – 0.30 W/m2K would normally be specified for the combined new and existing façade, thus reducing the heat loss through the wall by 40 – 70 % (excluding windows and doors). Even lower U-values of 0.14 W/m2K have been introduced for over-cladding systems renovating to passive house standards. This U-value should also take into account any thermal bridging through the attachments which can be responsible for 15 – 30% of the heat loss of the exterior wall.

If an air-tightness membrane is required, it should be positioned carefully in order that it does not add to the condensation risk. Ideally it should be internal to the building, but if this is not practical, it should be on the inside of the new insulation. It should also be vapour permeable if moisture emanating from the building fabric is to evaporate.

A list of key design criteria for over-cladding systems was developed (Table 5.2) and national criteria compared.

5.5 Dimensional accuracy in over-cladding Over-cladding solutions require highly accurate survey data of the external walls of the buildings in order to ensure that the components will fit without having to make alterations onsite. A study was therefore carried out of the issues that govern the accuracy of laser scanning in order to examine whether laser scanning provides sufficiently high definition and accurate survey data for designing and fabricating prefabricated steel over-cladding solutions. Current steel over-cladding systems allow for a tolerance to the fixing points of about 5 mm in all directions. The accuracy of the data gained from the survey of the existing surfaces to be over-clad must therefore fall within this limit. Steel cladding presents a precise, smooth finish where any unevenness or irregularity of spacing of panels will be very obvious to the observer.

The types of buildings that are upgraded by over-cladding are often very tall and the facades are difficult to access for manual survey techniques. Laser survey provides accurate dimension surveys of buildings to be renovated. Laser surveying allows three dimensional measurements to be made from a distance and, if sufficiently accurate, could be an essential tool for preparing the necessary data on which prefabricated steel over-cladding of large buildings could be designed and fabricated.

Several features of a laser scanner contribute to the level of definition it is capable of achieving in a high-definition survey. Since the greatest differentiating technical feature of a laser scanner, compared to traditional survey tools, is the detail it can collect, it helps to clearly understand these key contributing features:

Scan density and spot size (or beam diameter).

Scan noise.

Edge effects.

Resolution.

Range accuracy.

Angular accuracy.

Surface reflectivity.

Environmental conditions.

The required level of accuracy at a distance up to 50 m is near the limit of the capabilities of the laser survey technique. Only the most accurate laser scanners and rigorous field procedures allow laser scanning to be successfully used in this application. Very fine scanning capability (e.g., 1.5 mm grid spacing) and small spot size (~ 5 mm) are essential. In order for the measurements to be of sufficient accuracy for prefabricated steel over-cladding solutions, an accuracy of measurements within 5 mm in all directions must be achieved.


Table 5.2 Design criteria for over-cladding systems

Criteria Limit Comment

Thermal Insulation (U-value)

U-value of 0.25 W/m2K is proposed as the maximum value for over-clad walls to meet future Regulations. In the future, it may be necessary to move to lower U-values of 0.1 to 0.15 W/m2K

The U-value of the new over-cladding and the existing wall should be combined but taking account of any air movement behind the over-cladding. The effects of cold bridging through the attachment points should also be calculated. The future energy policy may require over-cladding to higher standards than current regulations.

Air- tightness Air leakage rate from the over-clad building <5 m3/m2/h. For superior performance, air leakage rates <2 m3/m2/hour.

The air leakage will be affected by the performance of the existing façade, and air movement in the cavity behind the over-cladding.

Design Life Sub-frame 60 years Cladding 30 years or 15 years to first maintenance

The sub-frame and its attachments should have a longer design life. Cladding panels should be removable, if damaged in the future.

Wind Loading Design for local wind pressure based on 50 years return period. Minimum negative pressure 0.8 kN/m2 locally

Wind pressures determined to national Codes. Wind suction (negative pressure) will be highest at the corners of the building. Pressure equalisation behind the new cladding may occur, which reduces local pressures.

Self Weight Self weight of over-cladding ( 0.5 kN/m2) acting at an eccentricity depending on the attachment system

Self weight of the over-cladding causes bending at the attachment points to the existing building. Typical minimum eccentricity = 100 mm.

Fire Resistance Fire resistance of over-cladding 30 mins. Cavity barriers prevent passage of smoke – barriers are placed at 6 m centres

The over-cladding system should prevent spread of flame, and should have some inherent fire resistance. Cavity barriers are required at not exceeding alternate floor positions i.e. 6 m vertically.

Acoustic Insulation

Airborne sound reduction 30 dB + Ctr

No specific acoustic insulation limit is specified, but a strict limit may be required for buildings adjacent to motorways or railway lines.

Windows Double glazed (low emissivity) U-value 1.5 W/m2K

The heat loss through the windows should be calculated (especially patio doors).

Balconies and Attachments

Attachments to be made to additional structural members e.g. SHS posts or to the floors of the building

No reliance is to be made on the existing façade as regards resistance to high local forces. Square Hollow Section posts may be attached to the existing floors by resin anchors.

Fixings and sub-frame

Attachments may be made to a steel sub-frame or to the existing structure

Fixings to the existing façade should be made with caution. A separate steel sub-frame is preferred with suitable fixings to the original structure at floor or column positions. Design the reliability of the systems for possible loss of one or more fixings

Limit solar gain Consider external shading on south or west elevations

Limiting solar gain is necessary to reduce over-heating in highly insulated buildings.

Renewable energy technologies

Consider photovoltaic panels or tiles, solar collectors or other techniques as part of overall energy balance.

Attachments of PV or solar panels may be required on south facing facades. Fix to sub-frame rather than to the existing cladding


5.6 Impact of air-tightness on energy demand (Reference should also be made to Section 6.4 which covers strategies for achieving air-tightness in industrial buildings.)

The air-tightness of the building envelope can provide important energy savings for both heating and cooling of buildings. Energy is lost through the building envelope by three main routes:

Building fabric losses, through the plane of the building element, including windows.

Thermal bridging, through building details and areas of reduced thermal resistance.

Air flows through the envelope structures, joints and interfaces, subsequently requiring heating or cooling to the building’s ambient temperature.

As thermal insulation levels increase, the influence of air leakage on the overall energy use becomes more important (Figure 5.3), particularly in the residential sector, but also for offices or buildings where the ventilation rate is high. Poor air-tightness causes air flows contributing to a building's total ventilation. This air flow by-passes the ventilation heat exchange, thus increasing the energy loss in the renovated building. At the same time, uncontrolled air flows cause thermal comfort problems. Another important consequence is that humid indoor air flows can cause condensation inside the envelope structure, especially in cold climates.

In existing buildings, air-tightness is often poor, mainly due to imperfect joints between the components. Even in buildings constructed to recent standards, the air leakage rate can be high and unwanted leakage of the warm internal air can represent 10 to 20% of the overall energy use for heating.

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Existing building Over-cladding of wallsand roof

Improved air-tightness New windows

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Figure 5.3 Relative impact of energy saving measures on a residential building's heating energy demand Note: New windows can be factory installed in prefabricated over-cladding systems

For buildings constructed to higher modern thermal insulation standards, this level of air leakage can increase proportionately to 20 to 30 % of the overall heating (or even cooling) energy use, and therefore it is important to reduce air leakage whilst maintaining good levels of air quality and controlling condensation. In new light steel framing construction, it is possible to achieve air-tightness levels of 0.6-1.0 litre/h (at 50 Pa), provided that measures are taken to eliminate air leakage at joints between building components, service points and in all connections in general.

In over-cladding of existing buildings, the build-up of external layers does not necessarily have a major impact on the air-tightness of the renovated facade, especially if the major contributor to


leakage is through the joints in the existing façade. Furthermore, if the over-cladding system is in the form of a ‘rain-screen’, then ventilation behind the new cladding is required to achieve pressure equalisation. Also some ventilation through the existing façade is required to avoid consideration (in the absence of a vapour barrier on the inside of the building).

Therefore, it follows that reduction of air leakage in over-cladding systems is technically difficult to achieve unless a strategy exists for improving the quality of the joints in the existing building. For low rise buildings, control of leakage at the wall roof junction is also important.

The air-tightness of a structure depends mainly on two layers in the structure: air barrier on the inner side of the thermal insulation, and wind barrier on the outer side of the thermal insulation. An air barrier and wind barrier are not necessarily separate layers but layers of a structure's normal composition, e.g., plastered internal facing or rendered facade of a wall. For the design of an air barrier, the following rules were developed:

A material layer that has a recommended air permeability of 1 10-6 m3/m2s Pa maximum, including all joints, e.g. a plastic film vapour barrier with over-lapping and sealed joints. An air barrier is possible by;

Adding a membrane on the inside of the building with an additional layer as the finished surface. A 30 mm cavity may be introduced between the interior boarding and existing wall in order to allow for services to be passed through it. Special attention should be paid on the wall to roof and wall to floor connections, as it may be impossible to seal these connections thoroughly only from inside.

Adding a membrane externally to the load bearing structure or existing façade with at least 75% of the total thermal insulation capacity outside the air barrier layer to avoid any condensation on air barrier.

The air barrier needs to be continuous over the whole building envelope area, especially at the connections between building parts, service installations, etc.

Window or door frame to wall connections should be filled with insulation, and sealed from both sides. It is recommended to use positioning systems for windows because of their heavy weight and the necessity to provide good connection with the structure without gaps, or to integrate the windows in a prefabricated walling system.

Ventilation ductwork installation should be located inside the air barrier. Only fresh air and exhaust air ducts should penetrate the air barrier.

The HVAC and sanitary installations and service penetrations of electricity, water, gas, and etc. systems should be sealed using flanges or other means of tightening either on the existing wall or inside the new over-cladding system.

Boarding or concrete element structures with sealed joints, fair-faced inner brick walls with plaster perform as air barriers.

Closed-cell insulation board externally to the existing wall with sealed joints also acts as an air barrier.

A wind barrier refers typically to a layer outside an insulated structure that protects the thermal insulation. It should be continuous over the whole building envelope. The importance of a wind barrier also increases especially with thick insulation layers. All insulated facades should have an air barrier which is provided by:

A material layer that has air permeability of 3 10-6 m3/m2s Pa maximum, including all the joints.

Wood fibre, gypsum or other board with sealed joints.

Exterior insulation system with render.

Wind proof mineral wool or EPS insulation with sealed joints.

Fair-faced brick wall without air gaps between insulation and brick wall.


Alternatively, local barriers may be introduced across all joints in the existing façade and junctions between components. This will not act as an effective air-barrier if there are many gaps and sources of air leakage, but it may be more sensible to identify the main points of leakage before embarking on the use of a continuous membrane. In addition, all joints around the windows and other penetrations should be sealed. The junction between walls and the roof is also a potential area of air-leakage which should be addressed.

These strategies depend on the type of over-cladding system that is used, i.e.:

Rain-screen façade allowing for facade ventilation.

Face-sealed façade (minimal air movement).

Trickle ventilation system (i.e. with modest air movement).

5.7 Study of the hygrothermal performance of an insulated over-cladding system

5.7.1 Description of over-cladding system

A hygrothermal (i.e. humidity and temperature) analysis of an over-cladding system subject to varying outdoor climate data, solar and long wave radiation, wind and driving rain was carried out based on dynamic heat and moisture calculations using the Wufi Pro 4.1 VTT program. The analysed system is shown in Figure 5.4, which is attached to an existing concrete wall. A rain-screen comprising a sheet steel panel protects the over-cladding system from the outdoor climate. A typical use of the system is in the renovation of old concrete panel façades in which the exterior concrete layer is removed. Therefore, the surface for installing the system is usually not perfectly even.

123 4 5 6 71. Rain screen facade2. Ventilated air gap 20 mm3. Windproof layer, 2 options

• GB: gypsum board 9 mm • FC: fibre cement board 4 mm

4. Mineral wool insulation – 3 options: • 150 mm/200 mm/250 mm

5. Inner board – 3 options• SP: sheet steel 0,6 mm • GB: gypsum board 13 mm • MG: metal grid

6. Non-ventilated cavity 50 mm 7. Existing concrete wall 160 mm

Calculation points (a) Isometric view (b) Cross-sectional through wall

Figure 5.4 Cross-section of the analysed facade system

The analysed structure has a ventilated facade with a ‘rain-screen’. The indoor temperature and humidity level were based on definitions in EN 15026 [6] and corresponds to normal activity, i.e. the temperature varies between 20 and 25oC and relative humidity (RH) between 30 and 60%. The outdoor conditions are based on reference years in different locations. The following climatic zones were analysed:

Cold continental (e.g. Moscow)

Cold marine (e.g. Riga)

Moderate continental (e.g. Berlin)

Moderate marine (e.g. London)

Warm continental (e.g. Bucharest)


The most comprehensive study was made for the cold continental climate. On the basis of these results, potential problems for other climates were studied. The model takes into account both long and short wave radiation and driving rain.

5.7.2 Indicators for performance and robustness of the system

The performance of the system was studied by calculating and analysing

RH (%) of the critical boundaries: exterior side of insulation and the layer between the old and new construction.

Moisture accumulation risk, w (kg/m3) in the insulation.

The location of these parameters in the system is illustrated in Figure 5.5. The relative humidity was recorded as hourly values on the exterior side of the exterior insulation system, and the interior surface of the interior board of the wall system. Also, the robustness of the system to imperfections was studied. The following variables were investigated:

Ventilation rate of the non-ventilated cavity, n = 0 h-1 or 1 h-1.

Driving rain leakage (DRL) into the non-ventilated cavity (together with ventilation options), of 0% or 1% of DRL.

• Ventilation rate of this air layer = 0 or 1 ach

RH (%)

w (kg/m3)

• Simulation of water leak from driving rain (DR) in this layer = 0 or 1 % of DR

• Ventilation rate of this air layer is always good = 100 ach • Ventilation rate of this

air layer = 0 or 1 ach

RH (%)

w (kg/m3)

• Simulation of water leak from driving rain (DR) in this layer = 0 or 1 % of DR

• Ventilation rate of this air layer is always good = 100 ach

Figure 5.5 Performance parameters

The ventilation rate and ingress of the driving rain into the cavity between the old and the new construction are potentially important parameters in this study. When installing the over-cladding system, the system is sealed to the old façade and, at least in theory, this cavity can be assumed as non-ventilated with no penetration of driving rain. In the cavity, there are strips of mineral wool insulation across and around the perimeter of a wall element. This also reduces the internal convection in the cavity. On the basis of assumptions on a crack size in the sealant and the existing air pressure, it was estimated that the maximal air change rate in the cavity would be about 1 ach*. The HEAT2 software was used for the 2-dimensional calculations to analyse the effect of thermal bridges on the performance. The effective thermal conductivity of the perforated C-profile is assumed to be 6 W/mK, which represents a reduction of 88% in the thermal conductivity of a solid web C section.

One performance indicator deals with the relative humidity and moisture content of the insulation of the wall system. For a good performance, the RH should not be above 80% for extended periods and no accumulation of moisture in the insulation is allowed. Also, the relative humidity between the old structure and the renovated system should not be above 80% for extended periods. The worst case scenarios were simulated for relative humidity on the cold side of the layer.

* ACH is an acronym for Air Changes per Hour and is a measurement of air infiltration. It is the total volume of air in a building that is turned over in one hour.


The results are therefore given separately for the wall system insulation, as follows:

RH(t) for different solutions.

Max. RH as a simple indicator for comparing the solutions.

Change in moisture content during the 3rd year gives moisture accumulation risk or drying potential.

For the cavity between the old and the new structure:

RH(t) for different solutions.

Max RH as a simple indicator for comparing the solutions.

Role of the ventilation rate and the effect of water intake.

The 3rd year of simulation was used for analysis, as it is normally an effective calculation period to achieve quasi-steady conditions.

5.7.3 Results

Impact of climate

The simulation results show that for a relatively vapour permeable structure, the air humidity in the non-ventilated cavity is not too high in any of the studied climates. The relative humidity of the cold side insulation, on the contrary, can become rather high for all climates except warm continental. The high humidity and low temperature in winter is not as critical as high relative humidity in summer.

Impact of insulation thickness and diffusion resistance

Comparisons were made with different insulation thicknesses and a vapour permeable inside board of the retrofit system (gypsum board GB) or vapour impermeable board, e.g. sheet steel SP. The insulation thickness has almost no impact on the hygrothermal performance of structures. The inner face of the retrofit system needs to be ‘vapour permeable’ to prevent moisture accumulation between the old structure and retrofit system. The existing structure of concrete (assumed to have no cracks) is still more diffuse than a sheet steel layer, and therefore the relative humidity of the cavity will rise. The insulation thickness of the diffuse structure increases the drying potential in all climates.

Impact of ventilation of the non-ventilated cavity

Small ventilation of the cavity between the over-cladding system and the existing structure reduces the relative humidity of the cavity and helps to control the moisture performance in the case of sheet steel on the inner face of the retrofit structure. For other structures, ventilation has almost no effect, or causes a slight increase in already low relative humidity. If driving rain penetrates into the structure, the peaks in relative humidity increases for all structures. The ventilation of the cavity has only a very slight impact, except for the structure with the sheet steel on the inside of the retrofit system. The drying capacity of the external insulation depends on the properties of the exterior board, e.g., gypsum board on exterior has better drying capacity than fibre cement board. The maximum relative humidity of the insulation increases slightly with increasing insulation thickness.

Conclusion

Generally, the investigated retrofit system demonstrated good hygrothermal performance in all climates, independent of the insulation thickness. The presence of slight or no ventilation of the cavity between the old and new structure also has little effect. Finally, moderate water intake e.g. from driving rain has little effect on the performance of the system.

An exception is the structure with a thin sheet steel plate on the interior side of the retrofit system. The hygrothermal performance of the structure is not acceptable unless there is slight ventilation of the cavity between the old and new structure. The critical climates for the hygrothermal performance are cold continental climate and moderate marine climate.


5.8 Analysis of thermal performance of double skin facades This study focused on three types of double skin facade systems:

Openable inner skin with mechanically ventilated cavity and controlled flue intake.

Sealed cavity, either zoned floor by floor or with a full height cavity.

Acoustic barrier, with either a thermally massive or a lightweight exterior envelope.

The thermal convection flow in the double-skin wall was investigated and compared with a reference wall in terms of heat transfer capacity, for various concrete layer thicknesses (Figure 5.6).

Figure 5.6 Reference wall (left) and the double-skin wall (right)

The walls are based on a three-layer solid slab of steel, insulation material and concrete. In the double-skin wall configuration, the steel plate and the insulation are separated by a column of air. The steel wall is attached by a series of thin steel fixings, which ensure the stiffness of the assembly but also create a thermal bridge between the external environment and the solid slab.

Due to the solar radiation on the steel wall, its temperature increases and a flow is induced by natural convection, affecting the global heat transfer of the ‘stack’ effect. The Fluent software program was used to perform the thermal convection analysis of the double-skin wall. The goal of this study was to evaluate the heat transfer coefficient of the double-skin wall and compare it with the reference wall. The double-skin wall leads to a significant improvement in insulation (Table 5.3) and the analysis showed that the U-value of the double-skin structure is 4.5 times lower than the reference.

Table 5.3 U-values of reference wall and double-skin wall according to concrete thickness and fixed insulation thickness (50 mm)

Concrete thickness, mm

Reference wall, without air W/m2K

Reference wall, with air W/m2K

Double skin façade W/m2K

90 0.768 0.183 0.157

120 0.758 0.182 0.155

150 0.749 0.182 0.154

200 0.732 0.181 0.151

250 0.717 0.180 0.149


5.9 Whole building thermal modelling of renovated buildings

5.9.1 Office building

Thermal simulations were carried out on a model of a 4 storey office building, based on a simplified version of an office built in the 1970’s with identical floor plans (Figure 5.7). (It was adapted from a test building for office simulations carried out in LVIS 2000 (HVAC 2000) energy research programme.) The simulations were carried out for four locations: Helsinki (Finland), London (UK), Moscow (Russia) and Berlin (Germany). The building had a net floor area of 3520 m2 and total floor area of 3664 m2. The original and retrofit data describing the building are presented in Table 5.4.

Office building

Floor plan Figure 5.7 Office building used in simulations

The heating set point was taken as 21ºC and the cooling set point was 24ºC. The cooling operates from 06.00-20.00 on week days when required. The heat distribution system is by radiator heating, based on district heating. Ventilation also provides cooling. Windows have no additional shading. The operating hours for ventilation are 06.00-20.00 on week days. The basic air change rate is 1.21 h-1. The annual heat recovery efficiency is 50% in both the original and renovated case. The heat recovery and space heating are turned off during June - August.

One person-load creates 75 W of sensible heat† and 38 W of latent heat‡ (113 W total). 70% of the sensible heat load is considered to be heat transfer by radiation to the surrounding surfaces, and 30% heat transfer by convection to the surrounding air. These values apply for a room temperature of 25°C. The thermal load of one computer or wide screen projector is considered to be 200 W. The office rooms have one computer per person, and the meeting rooms are equipped with wide screen projectors. Of the device heat load, 30% is radiation to the surrounding surfaces, and 70% in

† Sensible heat is the energy exchanged by a thermodynamic system that has as its sole effect a change of temperature. ‡ Latent heat is the amount of energy exchanged that is hidden, meaning it cannot be observed as a change of temperature. For example, during a phase change such as the melting of ice, the temperature of the system containing the ice and the liquid is constant until all ice has melted.


convection to the surrounding air. The lighting heat load is 15 W/m2, and 60% of the load transfer is by radiation to the surrounding surfaces and 40% by convection to the surrounding air.

Table 5.4 Data for original and renovated office building

Original Structure (data from outside)

Total thickness mm

U-value W/m2K

Wall Concrete 60 mm, wood-wool 80 mm, concrete 160 mm 300 0.82

Roof Concrete 60 mm, wood-wool 80 mm, concrete 180 mm 320 0.81

Base floor Gravel 200 mm, concrete 100 mm, wood-wool 100 mm, concrete 60 mm, filler 20 mm

480 0.63

Floor slab Filler 20 mm, cored slab 310 (190+120), filler 20 mm 350 2.1

Window 2 glass panes (glass thickness = 4 mm), air gap 60 mm 68 2.6

Renovated Structure (data from outside)

Total thickness mm

U-value, W/m2K

Wall Cement fibre board, 4 mm thick Mineral wool 150/200/250 mm thick Mineral wool/air (2/3 air) 50 mm, concrete 160 mm

364 (150) 414 (200) 464 (250)

0.25 0.20 0.17

Window 1 New windows according to the national building code 1.40

Window 2 Passive house standard windows, g-value 0.35 0.81

Table 5.5 and Table 5.6 show the various simulation results. Annual space heating and cooling demand for each climate are given as total demand (MWh) and specific demand (kWh/m2 gross floor area).

Improved thermal insulation of an office building results in decreased space heating demand but increased cooling demand. No passive cooling measures were taken into consideration in the simulations. (For example, exterior shading could help to reduce the cooling demand by roughly 50% in the renovated cases.) In general, renovation design of buildings with high internal heat gains needs to be carried out as a whole building approach. Thermal insulation improvement is beneficial from the energy point of view in all climates, but it can increase the consumption of electrical energy due to cooling.

Table 5.5 Annual heating demand in Helsinki, London, Berlin, and Moscow

Structure Window U-valueW/m2K

Annual heating demand, MWh (kWh / m2 gross floor area)

Location Helsinki London Berlin Moscow

Original structure 2.5 439 (120) 194 (53) 245 (67) 394 (108)

Renovated structure

1.4 227 (62) Insulation = 150 mm thick

0.8 191 (52) 72 (19) 97 (27) 173 (47)


0.8 185 (50)


0.8 181 (49) 67 (18) 91 (25) 163 (45)


Table 5.6 Annual cooling demand in Helsinki, London, Berlin, and Moscow

Structure Window U-valueW/m2K

Annual cooling demand, MWh (kWh / m2 gross area)

Location Helsinki London Berlin Moscow

Original structure 2.6 22 (6) 40 (11) 52 (14) 36 (10)

Renovated structure


0.8 43 (12) 69 (19) 75 (21) 54 (15)


0.8 44 (12)


0.8 45 (12) 71 (20) 77 (21) 55 (15)

5.9.2 Office building with roof-top extension

In order to study the effect of a vertical extension on the energy performance of a building, thermal simulations of one to three additional storeys added to an existing office building were carried out. In the first set of analyses, the properties of the ‘original state’ were assumed for the whole building including the additional storeys, then the ‘starting point’ for the refurbishment was taken for a second set of analyses.

additionalstoreyadditionalstoreyadditionalstorey

Figure 5.8 Simplified roof-top extension office building

The results of the thermal analysis of the office building are presented in Table 5.7.

Table 5.7 Heating energy demand (whole year, specific values, existing building with vertical extension)

Case Number of storeys Helsinki Berlin London

4 (starting point) 108.1 64.5 43.5

5 102.9 60.8 40.5

6 99.9 58.4 38.4

Base case prior to renovation (kWh/m2a)

7 97.8 56.7 36.8

4 (starting point) 55.5 30.0 17.6

5 53.2 28.1 16.1

6 51.8 26.9 15.2

Renovated building with additional floor (kWh/m2a)

7 50.7 26.1 14.5

The main benefit of the vertical extension is the reduced surface area : volume ratio of the building because the additional storeys do not increase the ground and roof areas, only the façade area.


For the commercial building sector, cooling energy demand is relevant and Table 5.8 presents the cooling demand for the three locations. An increasing compactness does not lower the energy demand for cooling, and also improving the U-value during the retrofit has no beneficial effect on the cooling demand. Thus, for the cooling case other strategies have to be developed for reducing the energy demand (for example, better shading and an improved ventilation strategy).

Table 5.8 Annual cooling energy demand of renovated building and its vertical extension

Cooling demand of renovated building Helsinki Berlin London

4 floors (starting point) kWh/m2a 10.2 17.5 14.4

5 floors kWh/m2a 10.8 18.4 15.1

6 floors kWh/m2a 11.2 18.9 15.7

7 floors kWh/m2a 11.5 19.3 16.0

5.9.3 Apartment building The simulated apartment building is four-storeys high and consists of a basement and three upper storeys. The basic construction of buildings of this type is concrete sandwich panel exterior wall, low-sloping roof with internal drainage, and concrete balconies attached to the inner slab of the panel. Typically, the insulation level in the renovated walls varies between 80 and 120 mm of mineral wool. The original wall technology renovated as well, and concrete passing through the insulation was common.

Renovation of the facades typically requires dismantling of the outer face of the panel if the durability of the concrete is poor. Also, balcony slabs have to be removed for additional insulation. Table 5.9 shows the dimensions of the analysed building. The windows are located on the main facades only, and in the simulations they are assumed to face south and north. The windows areas on the south elevation are 132 m2 and on the north 73 m2. The total window area is 19.7% of the total wall area.

Table 5.9 Key dimensions of the apartment building

Inner dimensions

Width 10.5 m (between the inner surfaces of outer walls)

Length 52.5 m (between the inner surfaces of outer walls)

Floor height 2.7 m, basement 2.1 m

Internal height 2.4 m, basement 2.1 m

Outer dimensions

Width 11 m (between the outer surfaces of outer walls)

Length 53 m (between the outer surfaces of outer walls)

Areas

Net floor area 550 m2 (one floor), 2200 m2 (all floors)

Gross area 583 gross.m2 (one floor), 2332 gross.m2 (all floors)

The heating set points are 21ºC for apartment floors and 19ºC for basement. There is no cooling. Typical heat distribution system is radiator heating based on district heat. Mechanical exhaust ventilation is assumed to be on 24 hour/day with an air change rate of 0.5 h-1. In the original building there is no heat recovery from ventilation. After the renovation, the annual heat recovery is assumed to be 75%. The original air-tightness (n50) of the building is 3.0 h-1. After the renovation, the air- tightness is about 1.0 h-1. The materials used in the original and retrofitted apartment building are given in Table 5.10.


Table 5.10 Data for original and renovated apartment structure

Original Structure (from outside)

Total thickness, mm

U-value, W/m2K

Exterior wall Concrete 60 mm Insulation 80 mm Concrete 120 mm

260 0.5

Interior wall Concrete 200 mm 200 2.6

Roof Insulation 150 mm, concrete 150 mm 300 0.3

Base floor Insulation 80 mm, concrete 100 mm 180 0.4

Floor slab Concrete slab 300 mm 300 2.7

Window 2 glass panes (glass thickness = 4 mm), air gap 60 mm 68 2.6

Renovated Structure (from outside)

Total thickness, mm

U-value, W/m2K

Exterior wall Mineral wool 250 mm Concrete 60 mm Insulation 80 mm Concrete 120 mm

510 0.16

Roof Mineral wool 300 mm Insulation 150 mm Concrete 150 mm

600 0.11

Base floor Insulation 80 mm Concrete 100 mm Insulation 60 mm

240 0.22

Window Passive house type windows, g-value 0.35 for the glass area — 0.81

Table 5.11 shows the simulation results for the apartment building. Annual space heating and cooling demand for each climate are given as total demand (MWh) and specific demand (kWh/m2 gross area).

Table 5.11 Annual heating demand in Helsinki, London, Berlin, and Moscow

Structure Annual heating demand, MWh (kWh / m2 gross area)

Location Helsinki London Berlin

Original structure, no heat recovery 212 (91) 107 (46) 126 (54)

Renovated: Ventilation increased 50%. Window transmissions decreased 40% for June - September. Heat recovery efficiency is 75%

39 (17) 8 (4) 15 (7)

The proposed renovation strategy reduces the heating demand of the building down to a level typical for passive house design. The simulation did not take cooling demand into account, which is expected to increase due to the improved thermal performance of the building envelope. Therefore, shading or louvres should be included.


5.10 Innovative over-cladding systems incorporating energy creation

A review was carried out of innovative cladding systems, suitable for renovation, which incorporated energy creation systems. The systems reviewed included dynamic insulation, vacuum insulated panels, phase change materials and solar shading.

5.10.1 Field testing of thermal storage wall system

The solar gain in south-facing elevations of buildings is significant. However, whereas the resulting heat flow can be an additional source of thermal energy in winter, in summer it can lead to over-heating. The use of thermal storage in thermally massive walls makes it possible to increase solar gain during cold periods and to stabilize the interior temperature in hot periods. The present study concentrated on the thermal storage wall constructed using light steel skeleton technology, designed both for south-facing elevations of new buildings and for the extension of existing structures with a southerly aspect.

Measurements were carried out in a climatic chamber whose internal temperature was maintained at about 20C, for thermal comfort of occupants. The external temperature was the result of the actual atmospheric conditions. To improve the performance of the thermal storage wall, heat insulating roller blinds were used. The cross-section and images of the designed thermal storage wall is shown in Figure 5.9.

The south-facing glazing heats up the absorber, which is made of black sheet steel. The steel quickly reacts to changes in temperature making the absorber work even during short periods of intense solar heat. The thermal storage wall accumulates thermal energy and transmits it to the interior, thus significantly reducing the consumption of energy. On the other hand, the delay in heat transmission is advantageous in summer as it prevents interiors from overheating. Thermal comfort is also enhanced by the heat insulating roller blinds, which reduce the temperature during summer days and limits heat losses during winter nights.

g

q4

q3

q2

q1

m3

m4

m2

m1

200 90 595 130 595 90 200

25

0 140

(a) Cross-sectional view

glazing (g)

mass-wall (m1, m2, m3, m4)

thermal isolation

heat-insulating roller

absorber

(b) Installation of thermal storage wall

Figure 5.9 Cross-section and photos of the thermal storage wall during assembly


Summer results

The analysis of the results obtained in summer was related to the effect of the heat-insulating roller blinds on the heat flow through the thermal storage wall. The results shown here refer to the central section of the wall. In June, the heat-insulating roller blinds were in the upper position, whereas in July, August and September they were lowered at sunrise and lifted at sunset. As a result, during the day the blinds prevented the absorber from overheating and at night their upper position enabled the heat to escape.

The solar radiation on the absorber created a high temperature, which resulted in over-heating of the accumulation layer and an increase in the temperature of the internal wall that adversely affected the interior thermal comfort. The summer measurements are summarised in Table 5.12.

Table 5.12 Summary of summer 2008 monthly results from the thermal chamber

April 89.049 2.274 -5.745 10.663 27.354 27.528 26.988 26.728 26.817 28.052

May 94.315 6.087 -1.555 14.869 28.494 30.741 29.835 29.308 28.838 29.173

June 97.444 12.961 6.095 19.998 32.887 32.646 31.118 30.160 28.596 27.287

July 91.731 5.324 1.337 20.420 27.350 27.080 26.434 26.067 25.417 25.129

August 116.500 6.773 2.471 21.252 30.847 30.448 29.707 29.190 28.332 27.798

September 76.615 4.615 0.177 14.580 24.402 24.225 23.551 23.260 22.783 22.737

time

intensity of solar

radiation,

W/m2

density of heat flow on the internal surface of the mass-

wall,

W/m2

in the mass-wall

4/4

in the mass-wall

1/4

average monthly value

air in the chamber

average temperature, °C

in the mass-wall

2/4absorber

in the mass-wall

3/4

density of heat flow in the mass-

wall,

W/m2

external air

Heat-insulating roller blinds limited the heat flow in hot summer months (July, August). The average value of the heat flow density in July constituted only 20.9% of the value measured in June and in August only 40.5% of the June value. The thermal storage wall limited the fluctuations in the internal temperature caused by a high amplitude of external temperature and the intensity of solar radiation during the day. The use of the roller blinds significantly improved the thermal comfort of the interiors.

Winter results

In June the heat-insulating roller blinds were in the upper position and, in winter months, they were lifted at sunrise and dropped at sunset. As a result, the absorber heated up during the day and at night the heat-insulating roller blinds prevented the wall from cooling. Table 5.13 shows the summary of the results, and Table 5.14 shows the heat losses in the following cases:

The test wall based on the results obtained.

The test wall without the solar gain being taken into account.

A traditional wall with thermal isolation (for U = 0.30 (W/m2K).


Table 5.13 Summary of winter monthly measurements in the central section of the wall

March 96.919 2.832 -6.146 5.318 22.509 22.813 22.077 21.858 21.928 23.256

October 94.700 10.539 3.820 12.410 25.972 25.563 24.214 23.478 22.269 21.449

November 63.777 1.774 -2.382 6.723 18.538 18.784 18.253 18.232 18.229 18.741

December 42.441 -6.266 -10.135 2.328 13.719 15.161 15.459 16.590 17.119 19.297

January 46.730 -8.058 -11.509 -0.810 12.530 14.097 14.225 15.870 16.615 19.077

February - -2.497 -6.631 0.585 16.450 16.997 16.729 17.041 17.777 19.208

in the mass-wall

2/4

in the mass-wall

3/4

in the mass-wall

4/4

air in the chamber

average monthly value average temperature, °C

time

intensity of solar

radiation,

W/m2

density of heat flow in the mass-

wall,

W/m2

density of heat flow on the internal surface of the mass-

wall,

W/m2

external air

absorberin the

mass-wall 1/4

Table 5.14 Heat losses in the winter months

upper sector central sector bottom sector

upper sector

central sector

bottom sector

upper sector

central sector

bottom sector

March 2.519 4.572 3.020 7.644 9.422 4.479 4.059 4.004 3.393

October -3.575 -2.842 -1.215 3.913 4.748 2.432 2.078 2.017 1.843

November 0.165 1.715 2.044 4.924 6.109 3.206 2.614 2.596 2.428

December 6.363 7.541 6.918 7.199 8.913 4.644 3.823 3.787 3.518

January 6.526 8.563 7.879 8.433 10.446 5.449 4.478 4.439 4.128

February 4.456 4.456 4.456 7.071 8.836 4.956 3.754 3.754 3.754

in sector 16.454 24.005 23.104 39.184 48.473 25.166 20.806 20.598 19.065

all sector

month

63.563 112.823 60.469

researched wall based on the results obtained,

kWh/m2

researched wall without the solar gain being taken into account

kWh/m2

traditional wall with thermal isolation, the heat transfer

parameter U = 0,30 (W/m2K)

kWh/m2

The results of measurements conducted in the climatic chamber were confirmed by numerical analysis, which made it possible to analyse the effect of the thermal conductivity of the components of the wall during the various stages of the experiment.

Conclusions and recommendations from study

The study confirmed that the prototype thermal storage wall is a good solution for south-facing elevations. The experiment carried out in winter enabled the loss of heat in the wall to be determined. This was comparable to the heat loss in the traditional facades with thermal insulation with the heat transfer parameter, U = 0.30 W/m2. The best results were obtained for the upper section of the wall. The value of the heat loss in this section was 20.9% lower than the mean value in the entire wall. Further numerical analysis would enable the performance of the thermal storage wall to be optimised with reference to its configuration and the materials used.

5.10.2 Field trials on transpired solar collectors as over-cladding

This part of the project investigated the practical use of a novel Transpired Solar Collector (TSC), which is a variant of the Solarwall™ system, for the over-cladding of existing concrete or masonry buildings. TSCs are constructed by attaching perforated metallic sheets to the envelope of a building. This creates an air gap between the perforated sheet and the building envelope (plenum). Using a fan, the exterior air is drawn into the plenum through perforations in the surface of the metallic sheet ‘absorber’. As the air passes over the outer surface of the perforated sheet, heat is transferred by convection from the sheet to the air. The solar heated air drawn out of the plenum is ducted inside the building (see Figure 5.10). When solar heated air is not required, TSCs have a by-pass opening so that


the ventilation air stream can circumvent the perforated metallic absorber. The plenum is sealed around all its edges. TSCs achieve instantaneous thermal efficiencies of over 70 % with low capital investment costs. The economic payback is less than two years for large installations [7].

Reference 8 describes a recent application.

Figure 5.10 A schematic view of a transpired solar collector

The field trials were based on flat steel cassette panels rather than profiled sheeting, and are the first example of TSC in this type of panel. The use of TSC could potentially reduce the heating costs of a building significantly, when combined with external insulation in a more conventional over-cladding application.

Test building

The building selected for the tests is a tower block at Oxford Brookes University in the UK, which is now disused but is still serviced. The north east facing façade of the 12 storey building is shown in Figure 5.11. The south facing façade was over-clad on the lower two levels and this was extended onto the east facing facade. The metallic panels were manufactured from Corus Prisma colour-coated steel in Merlin Grey colour, with up to 2,500 perforations per m2. Two of the panels between the windows in each floor level were perforated and the other panels were unperforated.


Figure 5.11 Tower block at Oxford Brookes University used for over-cladding tests and a cross-section through the original concrete façade panel

Installation of over-cladding panels

The installation of the large cassette over-cladding panels was carried out in July and August 2009. The lower two storeys of the tower block were over-clad on the south face and also partially on the east face. The concrete wall construction by Bison dates from 1962 and consists of storey-high precast concrete panels in a double skin construction (75 mm external leaf, 25 mm insulation, 150 mm internal leaf), and is illustrated in Figure 5.11. The window panels of the original building projected 80 mm outside the flat panels between the windows. The whole building is supported on a podium level at second floor, from which the installation work was carried out.

The calculated U-value of the original concrete façade was 1.2 W/m2K, and the renovation strategy is designed to reduce the U-value of the over-clad wall to 0.25 W/m2K, whilst generating renewable heating using the novel TSC system.

The cassette panels were manufactured from 1.2 mm thick colour-coated steel. They were manufactured as typically 2.9 m wide 0.9 m high in order to suit the window pattern of the existing façade. The panels consisted of an edge return of 30 mm with stiffening ribs bonded to the rear face at approximately 1 m spacing, and were designed to be sufficiently stiff under wind pressure and to reduce the ‘oil canning’ effect of restrained thermal expansion under solar gain, which affects all flat metallic panels.

The supporting cold-formed steel rails were placed along the vertical edges of the panels and were manufactured in 200 mm wide 2 mm thick ‘top hat’ C sections. The vertically orientated rails were connected through to the inner leaf of the precast concrete wall by 120 mm long chemical anchors using 8 mm diameter stainless steel rods. The distance between the outer face of the over-clad panel and the external face of the original façade was 140 mm. The existing windows were not replaced.

Two cassette panel configurations on the south facing wall were installed, as follows:

The existing wall on the lower storey was insulated by 80 mm thick closed cell insulation board attached to the existing façade between the windows. A 30 mm cavity was created at the back of the over-cladding panels.

The existing wall on the upper storey height was un-insulated in order to compare its performance with the insulated panel tests, when influenced by the thermal inertia of the concrete panel behind. Therefore the cavity was 110 mm wide at this level.

On the east facing wall, the entire over-clad area was insulated by 80 mm thick closed cell insulating board. In both storey heights on the south facade, only two of the central cassette panels were


perforated, as illustrated in Figure 5.12. The periphery of the panels was sealed to prevent unwanted air ingress.

Figure 5.12 Location of the perforated panels on the south facing wall

Two 150 mm diameter holes were drilled through the existing concrete façade, which allowed air to be drawn into the building through the perforated panels. Extract fans with a flow rate of 60 to 120 litres/sec were attached to the inside face of the existing wall and the air speed through the flexible ducting could be measured internally.

The panels were joined along their horizontal edges and were fixed on their top edge to the vertical C sections. The panels were lifted into position from the inside of the scaffolding and, to do this, the scaffolding was set at 300 mm from the existing wall and was supported laterally through the opened windows of the building. The typical weight of a panel was less than 20 kg and could be easily manoeuvred into position. Closure pieces were then installed along the periphery of the over-clad area around the windows and on the corners. The completed façade is shown in Figure 5.13.

Figure 5.13 Completed over-clad façade on first two floors above podium level, Aug 2009


Results of monitoring study

A total of 42 gauges were installed as the construction progressed. Data is recorded at 30 second intervals and downloaded regularly. The flow rate adopted for the continuous records was in the range of 60 to 90 litres/sec/floor. At this flow rate, the air speed though the perforations was 3 to 4.5 m/sec. On certain days, tests were carried out at various flow rates to compare the temperature of the heated air and the quantity of heat energy with predictions. In general the experimental results support the energy balance predictions and prove that flat panel TSCs are a competitive over-cladding solution for residential and commercial buildings.

The ‘south facing’ wall was in fact orientated at south 10 degrees west. The building latitude was 51.7N and the longitude was -1.1W. These factors influence the solar radiance on the wall. The expected heating period on this façade orientation was from 11 am to 4 pm in the spring and autumn months. A weather station was installed on the podium adjacent to the south façade, which recorded external conditions and solar radiance. It was installed in early February 2010. Solar radiance was recorded on the horizontal plane and this was converted to the vertical plane for the precise orientation of the façade and time of the year.

The test results for a cool but sunny day of 25 September 2010 are presented in Figure 5.14, in this case showing the solar radiance measurements. The correlation between solar radiance and the response of in-coming air temperature is very close. At this time of the year, the heating period was from 10.30 am to 6 pm. The ambient temperature ranged from 5ºC at night to 12ºC during the day and the room air temperature was between 12ºC at night and 21ºC during the day. The incoming air temperature ranged from 19 to 29ºC during the heating period and the metal surface reached as high as 50ºC at 1pm. The solar radiance ranged from 200 to 750 W/m2 over the heating period.

The difference between the incoming air temperature and the room temperature was in the range of 5 to 8ºC. As noted above, the room temperature will rise due to both solar gain effects and incoming air. The internal wall temperature was approximately 15ºC during the day. It is necessary therefore to separate the effect of solar gain through the windows. Also, in the practical use of this technology, the heated air would be ducted to the cooler north side of the building in order to provide ‘free’ heating. It is considered that the reference internal temperature should be the internal wall temperature rather than the south facing test room, which may be taken as 12ºC for the data in Figure 5.14.

The data for a typical cold sunny day (10 February 2010) is shown in more detail in Figure 5.15. The ambient air temperature during the day was between 1 and 3ºC, and metal temperature varied from 5 to 37ºC (with an average of 20ºC). The incoming air temperature was in the range of 10 to 22ºC (average of 15ºC) in the heating period from 10am to 4pm (for the winter period). Solar radiance ranged from 100 to 600 W/m2 on the horizontal plane.

The internal room temperature ranged from 8ºC at night to 15ºC during the day. It is not evident how much of this temperature rise is due to solar gain through the windows and how much to the warm air brought in through the TCS. The internal wall surface temperature was consistently around 9ºC during the day, and this may be taken as the reference temperature. At the warmest part of the day, the incoming air temperature was about 5ºC higher than the room air, but 10ºC higher than the wall temperature, which is more consistent with the parts of the building not affected by solar gain.

The usability of the heat generated depends on the occupancy pattern and climatic conditions, which should be investigated in continuing research.


Figure 5.14 Test results for cool but sunny day (25 September 2010)

Figure 5.15 Test results for 10 February 2010


5.11 Design guidance on transpired solar collectors This design guidance applies to the use of transpired solar collectors (TSCs) in the renovation of residential and commercial buildings by over-cladding in which the over-cladding panels are large flat steel cassettes that are perforated to allow air to be drawn through the perforations.

5.11.1 Basic energy balance equations for TSC The instantaneous thermal efficiency of a TSC can be described using a flat-plate solar collector efficiency equation, which is the energy transferred to the outlet air stream divided by the total solar radiation incident on the perforated absorber surface:

p out ambi

T

mCn

T T

AG

(5.1)

where PC is the specific heat of ambient air i.e. the exterior air, A is the projected area of the perforated

absorber, m is the mass flow rate though the perforated absorber, outT is the air leaving the perforated

absorber, TG is the total solar irradiance incident on the absorber surface, and ambT is the exterior air temperature. Equation (5.1) can be rearranged to find the temperature of the air leaving the TSC.

Similar to flat-plate solar collectors, outT can be determined by performing an energy balance of the perforated absorber [9]. This energy balance is illustrated in Figure 5.16, and shown mathematically in Equation 5.2.

Figure 5.16 Simple energy balance on the perforated absorber

( ) ( )p out amb T rad col ambmC T T A G A h T Ta- = - - (5.2)

In Equation (5.2), is the absorptance of the perforated absorber, colT is the temperature of the

perforated absorber and radh is the linearised radiation heat transfer coefficient (linearising the radiation heat transfer coefficient is an effective means of converting the temperature to the power of 4 as described by the Stefan-Boltzmann law to a linear formula over a narrow temperature range). Equation 5.2 assumes that the wind heat loss can be neglected [10].

Given that the energy transferred to the outlet air stream is a function of the design of the perforated absorber, a heat exchange effectiveness (HEE) ratio ( HX ) is used to describe the relationship between the actual temperature rise against the maximum possible temperature rise:

out ambHX

col amb

T T

T T

(5.3)

where HEE is determined experimentally [11]. By rearranging the previous equations Equation (5.3) for outT , Equation (5.2) is transformed into:

( ) ( )p HX col amb T rad col ambmC T T A G A h T Te a- = - - (5.4)


The mass flow rate is expressed in terms of the suction-face velocity ( v ), which is defined as the velocity of air if it were to travel though whole surface area of the absorber:

air

mv

A (5.5)

where air is the density of ambient air. The resulting equation for instantaneous thermal efficiency is obtained [11,12]:

1 rad

HX air P

inh

C v

(5.6)

Equation (5.6) shows that the efficiency of the TSC is proportional to its absorptivity. Broadly speaking, absorptivity is highest in darker colours and careful design is required to balance aesthetics and thermal efficiency. Depending upon the application; colours such as blue, red, green and grey can be considered as having good solar absorptance characteristics.

Figure 5.17 demonstrates that TSCs are able to achieve instantaneous efficiency of over 70 % when operating at suction-face-velocities above 0.02 m/s. Operating a TSC at suction-face-velocities below 0.02 m/s results in lower instantaneous thermal efficiencies but higher air temperature rises.

Figure 5.17 Instantaneous thermal efficiency against flow rate for 3 wind velocities (based on the assumptions in RETScreen® V3.1 and using an absorptivity of 0.9)

Suction-face-velocities of 0.04 to 0.05 m/s are recommended for field installations to ensure the wind heat loss and ‘outflow’ do not compromise the performance of the TSC [10,12]. Outflow is where the heated air in the plenum exits through the TSC absorber, thus losing the heat generated. Gunnerwiek et al. [13] identified that if the site wind speed reached 5 m/s, outflow would be prevented if the TSC operates with suction-face-velocities of 0.0125 m/s under typical operating conditions up to 0.039 m/s for buildings with the wind incident on the collector at 45o.

5.11.2 Types of TSCs

TSCs are of three basic types: 1) a stand-alone; 2) envelope mounted south-facing wall; and 3) the roof-top mounted TSC. Figure 5.18 shows a south-facing type of TSC, also known as an envelope mounted TSC. In this type, the perforated metallic absorber is fixed to the building façade of either a new or existing building. As the TSC is incorporated onto the facade, the only additional components of the TSC are a metal sheet (the perforated absorber) and the spacer system.


Figure 5.18 SolarWall® TSCs installed on the south wall of Beaconsfield service station (UK), where the TSC preheats the ventilation air for the food court

The most common application of a TSC is to pre-heat the ventilation air, and the heated air is then generally heated further as it passes through the building’s HVAC system to reach the desired delivery temperature. In the summer, when there may be no requirement to heat the ventilation air supply, TSC systems have a means of by-passing the absorber.

The predicted integrated environmental and economic performance of TSCs is determined using either RETScreen® V3.1 Solar Air Heating Project Model [14], which is an Excel spreadsheet application using NASA surface meteorology and solar energy weather data to calculate energy savings on a monthly average time-step. It uses an efficiency equation similar to Equation (5.6), which takes into account the variables of absorptivity, airflow rate and wind speed. The energy saving calculated is the sum of the active absorber solar gain and wall heat recapture (heat loss through the wall is recaptured into the air stream).

The simplified energy yield model uses the efficiency algorithms researched in the IEA Solar Heating and Cooling Programme Task 14 [11] and can model pre-heating of ventilation air for most building types. TSC energy yield models are however not currently included in many of the building energy dynamic simulation software.

TSCs can also be combined with photovoltaic panels to create a hybrid photovoltaic/solar thermal panel (PV/T), i.e. a photovoltaic/transpired solar collector (PV/TSC), which simultaneously converts solar radiation into heat and electricity. There are two broad types of PV/TSC:

1. Bonded type - PV cells/modules are bonded directly to the absorber

2. Fixed type - PV modules are fixed to the absorber

The bonding of PV cells directly to the perforated metallic sheet was studied by Conserval Engineering Inc. [15,16], who verified that the PV/TSC was able to lower the temperature of the PV cells, but the PV cells also resulted in a reduction in the thermal efficiency of the TSC when compared to a standard TSC. Currently, there is no commercial PV/TSC of the bonded type, primarily due to the difficulty in manufacturing PV cells that can be economically bonded to the absorber.

The fixed type PV/TSC, where conventional PV modules are fixed to the absorber, has been commercialised with both the south wall form and modular form. In one study, the forced ventilation of polycrystalline silicone PV modules using a TSC system was able to reduce the operating temperature of the PV modules by 3 to 9oC.

5.11.3 Application of TSC to Over-Cladding Systems In this research, a TSC has been developed for the over-cladding of existing concrete or masonry buildings. This is based on a flat steel cassette panel rather than profiled sheeting, and is the first


example of TSC in this type of panel. It uses steel cassette panels manufactured in lengths of typically 2.9 m and widths of 0.9 m.

Part of the south facing façade of a concrete panel building was over-clad on the lower two levels and this was extended onto the east facing facade. This application is illustrated in Figure 5.13 in its completed form. The metallic panels were manufactured from colour-coated steel with up to 2,500 perforations per m2 and a porosity of 0.35% when expressed over the panel area (including the panel border). Two of the panels between the windows in each floor level were perforated and the other panels were unperforated.

Consider the results in Figure 5.15 obtained in a typical spring or autumn day for a south-facing perforated panel in which the typical heating period was from 11 am until 4 pm. The external steel temperature can reach up to 37C, although the average during the heating period is 25 to 30C. The average in-coming air temperature is approximately 20C. The reference room temperature is taken as that not influenced by solar gain (ie corridor or north facing room), which is on average 15C during the heating period. The incoming air temperatures are about 7C lower than the external temperature of the steel surface. During the heating period, the in-coming air is about 8C higher than the room reference air temperature.

Typical measured data are:

Temperature difference between in-coming and the internal air =10C average

Heating period (11 am to 4 pm in the spring and autumn) = 5 hours

Air-flow rate through the fan (approximate) = 60 litres/sec

Area of perforated panels (per floor) = 5.3 m2

The calculated energy generated per hour was 0.72 kW. Over a 5 hour period per day, this is equivalent to a heating energy of 3.6 kWh. Assume that 150 days per year have this level of solar radiance, this is equivalent to an annual energy input of 540 kWh. Assuming this heating energy is distributed over a building width of 5 m and length of 10 m, the equivalent saving in heating energy, is Qnef = 540/(5 10) ≈ 11 kWh/m2 floor area per year. This is equivalent to about 30% of the heating demand of the over-clad building. The heating energy provided by is approximately 136 W/m2, when expressed per unit area of the perforated panel.

The fan energy is rated at 0.1 kW at full flow rate of 120 litres/sec, and so the energy required to operate the fan over 5 years at half this maximum flow rate is about 0.25 kWh per day. This is equivalent to about 7% of the heating energy that is created.

Typical weather conditions over the year may be grouped as shown in Table 5.15 and may be used to predict the total benefit of this form of TSC in terms of reduced annual heating demand for a typical residential building.

These typical temperature scenarios may be used to calculate the:

1) Energy generated by the TSC due to solar radiance.

2) Saving in energy loss due to air leakage and conduction through the existing façade.

3) Fan energy when TSC is in operation.

The night time cooling of the cavity due to radiant effects on the metal surface may be neglected. Similarly, in hot summer conditions, the heated air may be expelled rather than brought into the room.


Table 5.15 Typical weather scenarios used to predict energy savings due to TSC cassette panels

Condition Room Reference Temperature

θroom C

In-coming Air Temperature

θcavity C

External Temperature

θext C

TSC Active

Bright cold winter day 15 22 3 Yes

Dull cold winter day 15 5 5 No

Bright spring day 18 27 12 Yes

Dull spring day 18 12 12 No

Warm summer morning 18 30 20 Yes

Warm summer day 22 35 25 No

5.12 Design guidance on renovating commercial/residential buildings

5.12.1 Over-cladding systems

Building dimensions

Over-cladding solutions for upgrading the thermal and weathering performance of existing buildings using prefabricated steel components requires highly accurate survey data of the external walls of the buildings. Accurate dimensions ensure that the components fit without having to make onsite-alterations. Laser scanning provides a high-accuracy measurement system for facade dimensions. Using laser survey techniques, the survey data of building facades can be gathered from the ground or adjacent buildings from a distance of up to 50 m.

Sufficient accuracy requirement for designing and fabricating prefabricated steel over-cladding solutions is 5 mm in all directions. Laser survey techniques can provide this level of accuracy as long as the correct instrument is used, the right techniques and software are adopted and environmental conditions and reflective surfaces are suitable.

Requirements for over-cladding

Before the over-cladding, a condition survey need to be carried out to investigate the rate of deterioration especially in corners and window to wall connections, and in concrete walls the concrete reinforcement steel corrosion. The following requirements are identified for a wall to be over-clad:

Clean wall: no health risks from mould etc

Bearing capacity: extra weight due to the frame, thermal insulation and cladding can be accommodated

Dryness: The wall has be dry or the over-cladding system has to enable drying of moisture

The renovation system should:

Be weather-tight

Support its own weight and the wind loads acting on it.

Reduce heat losses (to conform to modern Regulations).

Have a long service life (more than 30 years is recommended).

Respect country specific fire regulations

Smooth out the uneven and/or non-vertical walls.


The installation must be rapid to avoid moisture in the structure. Prefabricated systems are preferred for their quality and delivery cycle. In low-rise buildings up to 4 floors, prefabricated and building high elements allow for routing of new electrical and HVAC systems thus reducing the down time in the building.

Strategies to improve air-tightness in renovation

The strategy to improve the air-tightness in renovation depends on many issues including:

Building type and form

Condition and type of load bearing materials

Building system of wall or roof.

Window assembly

Facade penetrations

Location of the air-tight and vapour-tight layer in the existing structure

The possibility of intervention with the building during renovation work.

It is necessary to carry out an air-tightness test and infrared or smoke tests to locate the air leakages in the envelope structures. In existing construction, the poor air-tightness of the façade is largely due to the air leakage through the joints between the panels, blocks, building components and services penetrating the wall. In renovation of buildings, due to moisture performance, new insulation should always be placed externally to improve the thermal performance. The air leakage has to be reduced by additional measures. Furthermore, the air barrier that reduces air leakage should be positioned so as not to cause the risk of condensation. An additional vapour barrier may be required to eliminate risk of interstitial condensation, and this may also act as an air barrier.

It is important to identify the main points of air leakage before making a decision on measures to make the envelope more air-tight. Also, a proper fresh air flow for good indoor air quality has to be ensured as in old buildings the main ventilation comes through windows and air leakages in the envelope. Measures to improve the air-tightness include are given in 5.6.

Moisture performance of renovated facades

Generally, exterior thermal insulation systems for over-cladding have good hygrothermal performance in all climates, independent of

Insulation thickness

Slight ventilation or none of the cavity between the old and new structure

A moderate water intake e.g. from driving rain

An exception is a structure where a vapour tight layer is on the interior side of the over-cladding system. The hygrothermal performance of the structure is not acceptable unless:

The existing wall structure is completely dry (relative humidity < 50%) at the time of over-cladding

75% of the total thermal insulation locates outside the vapour-tight layer

The gap between over-cladding and existing wall is slightly ventilated externally .

In warm and humid climates, the risk of summer-time condensation should be analysed

5.12.2 Energy performance

Improved thermal insulation of an office or residential building results in decreased space heating demand but may result in increased cooling demand. The heating demand can reduce by 50 - 60 % with well-designed over-cladding and over-roofing with proper, climate depended additional thermal insulation and ventilation with heat recovery.


The additional thermal insulation level for renovation depends on the climate but also on the building type, form, building rights, etc. The following guidelines should be taken into account when designing energy renovation:

The target energy-efficiency level should be decided at the briefing of the project. The process should include all designers in the process. There are many voluntary techniques for very low energy buildings such as ‘passive house’ approach, Minergie standard or even net or nearly zero energy buildings. The decision is dependent on total costs and financing of the project.

An efficient energy renovation requires always a whole building approach. The best energy demand/cost ration can only be achieved by looking all aspects of energy efficiency improvement as a whole.

Reduced heating demand may lead to increased cooling demand. Passive cooling strategies should be applied to reduce or avoid the need for mechanical cooling.

A condition survey needs to be carried out to investigate the condition of the existing facades and to study the possibilities of over-cladding and over-roofing. In many cases demolition of the existing building is economically more beneficial that renovation

Increasing the thickness of a wall or a roof leads to other actions such as re-building the eaves, insulation of the foundations and due to architectural reasons also new windows or changing the position of the windows.

Additional insulation in walls and roofs become economically more beneficial in connection to necessary facade renovation.

New windows are seldom economically feasible. If the existing windows are technically in poor conditions and need to be changed, the energy benefit of new high performance windows can cover the extra costs compared to typical windows


6 WP2: RENOVATING INDUSTRIAL BUILDINGS: ENERGY EFFICIENCY STRATEGIES


6.1 Objectives This Work Package addressed the ways in which the thermal performance of single storey industrial-type buildings may be improved. An important task was the analysis of existing buildings before and after renovation. Solutions for the renovation of single span industrial-type buildings and the investigation of the as-built properties by numerical testing and measurement are also presented.

6.2 Problem areas in single storey buildings and examples of renovation

Detailed information on the thermal performance of industrial buildings was collected in order to identify weak points in existing forms of construction. To illustrate the thermal problems that may be encountered, infra-red (IR) surveys were carried out on a number of typical buildings, including a University research building in Aachen built in 1993 (Figure 6.1). The results of IR surveys carried out in December 2008 are shown in Figure 6.2. The IR images show the pattern of the cassette walls with regular thermal bridges. The parapet shows significant ‘hot spots’, which are caused by thermal bridges or by air movement.

Figure 6.1 RWTH building – south elevation

Figure 6.2 IR image of RWTH building – south elevation

A laboratory hall at Aachen University was renovated and extended by using steel members and cladding (see Figure 6.3). For the roof top extension, a new precast concrete slab was required. After


adding the slabs, steel beams were installed. The whole building (existing masonry façade and the building extension) were over-clad with sandwich panels. A further step to improve the energy efficiency was the installation of new windows.

Figure 6.3 Laboratory hall before and after renovation, Aachen

The Siemens factory at Congleton, Cheshire in the north west of England had a poor quality asbestos cement roof from the 1950s that could not be easily and safely removed whilst the factory was in operation. It was decided to over-clad the building by providing a new roof to improve its weather tightness and thermal insulation. The roof before and after renovation is illustrated in Figure 6.4.

The over-roofing was supported by attaching a light steel sub-frame called Instalok to the existing purlins, and then fixing 180 mm of mineral wool insulation and new profiled steel sheeting, along with new roof lights and ventilators to the existing roof. The total roof area was 4000 m² and the roof sheeting was Corus’ HPS colour-coated R32/1000. The U-value of the new roof was designed to be 0.25 W/m²K. The air-tightness of the building was also improved. The building was kept in operation during construction operations.

Figure 6.4 Industrial building before and after renovation, UK


6.3 Analysis of cassette walls with improved thermal insulation

The IR surveys of industrial buildings in lightweight steel construction make it clear that cassette walls as shown in Figure 6.5(a), can have poor thermal performance. Laboratory tests in a hot box support this finding (see Figure 6.5(b)).

(a)

(b)

Figure 6.5 Existing cassette wall (a), IR image of cassette wall from hot box test (b)

Thus, new solutions with improved thermal quality are needed. Two options were considered in this project, as shown in Figure 6.6:

a) Re-cladding using additional insulation,

b) Over-cladding using steel-sandwich-elements.

The re-cladding solution with additional insulation was studied in detail by FEM calculations and hot box tests. Figure 6.7 shows the re-clad solution (compare with Figure 6.5!) and the impact on the U-value is illustrated in Figure 6.8. An insulation thickness of 40 mm is recommended, which means that the wall system can reach a U-value of about 0.4 W/m²K.

Figure 6.6 Re-cladding with additional insulation layer (Rockwool: “Steelrock”, left), over-cladding using steel sandwich elements (right)


Figure 6.7 Hot box with IR camera (left), result for re-clad cassette wall (right)

100 mm Cassette wall with additional insulation layer (hins,a)

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0 5 10 15 20 25 30 35 40 45

hins,a [mm]

Um

[W

/m²*

K]

0,035 [W/m²*K] 0,040 [W/m²*K] 0,045 [W/m²*K] min. requirements (Ger)

Figure 6.8 Effect of additional insulation layer on the performance of steel cassette systems

The effect of an additional 100 mm insulation layer on the cassette wall and the use of steel-sandwich panels was studied by FEM calculation. The U-value of the façade can be improved from about 0.8 W/m²K for the simple cassette wall (100 mm deep) to 0.24 W/m²K by using a sandwich element of 120 mm depth and thermal conductivity, = 0.045 W/mK.


6.4 Strategy for achieving air-tightness in building renovation

(Reference should also be made to Section 5.6 which covers strategies for achieving air-tightness in residential and commercial buildings.)

Air leakage in both new and existing buildings is a major cause of energy loss. With increasingly stringent building regulations, building envelope air-tightness performance is one of the critical elements of low energy design. This section discusses building envelope air leakage, the effect of air leakage on building performance and regulatory requirements in Europe. It presents air-tightness data from physical tests of different types of buildings. It highlights the reasons for poor air-tightness performance and current bad practices together with best practice. The review informed the development of a practical strategy to achieve low air-tightness.

6.4.1 Air leakage

Building air leakage can be defined as the movement of air in and out of a building which is not purposely planned or intended for exhausting stale air or bringing in fresh air. Air leakage is driven by a combination of wind, a ‘stack’ effect and mechanical systems and will occur wherever there is a crack, gap or porosity in the external envelope. The rate of unplanned envelope air leakage must be kept minimal to avoid moisture movement into the cavity and build-up of condensation in the insulation, which could significantly reduce the life span of the building envelope.

Building envelope air leakage is a good measure of the overall quality of design, workmanship and construction of a building. Air leakage has four principle effects on the building performance:

Significant increases in space conditioning loads (heating and cooling).

Poor internal comfort conditions.

Degradation of envelope assemblies due to interstitial condensation and/or air driven rain penetration

Ingress of outdoor pollutants – dust, noise, etc

6.4.2 Air leakage regulatory requirement

Table 6.1 collates typical air leakage regulatory requirements in Europe. These values are likely to be substantially improved in the future. It is considered best practice that low levels of air leakage must be combined with the controlled ventilation strategy in order to maintain a good working environment within the building.

Table 6.1 Regulatory requirements in Europe for envelope air-tightness in new buildings

Country Type Value Unit

All building > 500 m2 10 m3/h.m2 @ 50Pa UK

< 500 m2 (to avoid test) 15 m3/h.m2 @ 50Pa

Belgium 3.0 h-1

Passive House 0.6 h-1

Mechanical Ventilated 1.5 h-1 Germany

Natural Ventilated 3.0 h-1

Finland 1.0 h-1

Offices 1.2 m3/h.m2 @ 4Pa France

Commercial 2.5 m3/h.m2 @ 4Pa


6.4.3 Poor air-tightness performance

Investigations carried out under this project have highlighted the key reasons for poor air-tightness performance of buildings. These can be grouped into the follow categories:

Pre design stage:

Ambiguous design specification,

Lack of clarity of desired level of envelope performance (particularly for refurbishment due to ambiguity in the regulatory requirement.

Design stage:

Failure to develop a strategy for air barriers at the early stage of design,

Too many materials within the envelope are used to form an air barrier,

Uncertainty on the position of the air barrier within the building envelope,

Many unsealed penetrations through the air barrier,

Interface detailing and penetrations are not well thought through to ensure air barrier continuity,

Lack of understanding of the performance of air barrier materials in terms of air permeability, buildability and durability of seals.

Construction stage:

Lack of communication between design and construction teams ,

No active quality control process leading to poor quality of workmanship,

No process to monitor and review design changes,

Several sub-contractors are involved in the construction works and none is responsible for the formation of critical seals.

6.4.4 Best practice guidelines for achieving air-tightness

In order to achieve low air leakage, measures need to be taken at the pre-design, design and construction stages. The following methods are recommended (those followed by a number refer to one of the details shown in Figure 6.9):

Air barrier seal at junction between vapour barrier and gutter assembly (1),

Air barrier seal to vapour control layer – welded laps,

Installation of air barrier tape seals to laps of internal steel of a built-up system,

Flexible self-adhesive membrane forming air barrier at wall to roof junction,

Tape seals forming air barrier continuity at joints between sheathing boards,

Therma-foil Plus on warehouse gable to ensure continuity of air barrier,

Therma-foil Plus seal on the outer side of the internal steel liner forming air barrier continuity of the roof (2),

Application of Therma-strip onto the roof sheet to ensure continuity of air barrier,

Over-cladding of the existing brick wall using a rain-screen system: breathable air barrier to ensure vapour control and limit air leakage (3),

Acoustic deck: breathable air barrier to ensure vapour control and limit air leakage,

Over-cladding of existing residential buildings: breathable air barrier to ensure vapour control and limit air leakage,


Over-cladding of existing industrial buildings using rain-screen systems: breathable air barrier to ensure vapour control and limit air leakage (4).

(1) (2)

(3) (4)

Figure 6.9 Techniques for achieving air-tightness in renovation

6.5 Thermal building simulations - parametric study Thermal building simulations were carried out to provide heating demand data to enable empirical relationships for the estimation of energy demands of industrial buildings before and after renovation to be derived. This enables the energy savings and related cost savings due to the renovation work to be estimated. The empirical relationships for heating demand were implemented in the Economic Justification Tool developed in Section 9.

6.5.1 Description of boundary conditions for the thermal analysis Table 6.2 summarises the size of the building, location, orientation, operation and occupancy pattern considered for the thermal simulations. As can be seen in Table 6.2, three climates (Berlin, Helsinki and London) were considered for the thermal simulations of a small and medium size industrial building.

Table 6.2 Building specification for thermal simulations

Small Medium

LOCATION 30 60 6 m 60 120 10 m

Berlin x x

Helsinki x x

London x x

Orientation: North/South and East/West

UK National Calculation Method Operation and Occupancy profile [17]:

Warehouse

Naturally ventilated

7am – 7pm for 7 days

SIZE


6.5.2 Parameters for thermal analysis

Table 6.3 presents the key parameters for the thermal analysis. ‘Base Case’ is the current state of the building. Table 6.4 gives the assumed parameters for occupancy, equipment, lighting and HVAC. These parameters are default values in the thermal simulation tool used for this analysis and are typical values for industrial buildings in the UK.

Table 6.3 Parameters for thermal analyses

Parameter influencing thermal performance

Base Case Current Practice

Good Practice

Better Practice

Best Practice

1 Air-tightness m3/(h.m2)@50 Pa 27 10 7 4 1

Cavity wall 1.7 0.35 0.25 0.20 0.15

Wall panel 2.3 0.35 0.25 0.20 0.15

Internal wall 1.7 1.7 1.7 1.7 1.7

Roof 1.95 0.25 0.20 0.15 0.10

Grd floor 1.0 0.25 0.20 0.15 0.10

Window 5.4 2.20 1.50 1.10 0.70

Rooflight 6.6 2.20 1.80 1.50 1.20

Solar shading (effective g-value) 0.85 0.65 0.50 0.35 0.20

Entrance door 3.0 2.20 1.50 1.10 0.70

Vehicle access door 5.9 1.50 1.30 1.10 0.90

2 U-value (W/m2K)

Roof ventilators — — — — —

3 Rooflights (%) 20, 12 20, 12 20, 12 20, 12 20, 12

Gutter (Valley)

Drip (wall ground fl.)

Roof – wall (Eaves + Verges)

Wall – corner wall

Wall – floor not grd.

Lintel (window/door)

Sill below window

4 Thermal bridge-values (W/(m.K))

Jamb (window/door)

Default method in NCM [17] to add 10% to U-value for each element

Lighting (W/(m2.100 lux)): office, storage & shed 4.5 3.75 2.5 1.75 1.25

Lighting (W/(m2.100 lux)): other spaces 6.0 5.2 4.0 3.3 2.5

Daylight Dimming No No Yes Yes Yes

Occupancy Sensing No No Yes Yes Yes

Specific fan power (W/(litre/s)): centralised balanced

3 1.8 1.5 1.1 0.9

Heat recovery effectiveness (%) 0 0 60 70 80

Heat generator seasonal efficiency 0.65 0.84 0.9 0.95 1.15

Cooling generator Seasonal Energy Efficiency Rating (SEER)

— — — — —

Hot water generator seasonal efficiency 0.50 0.70 0.8 0.90 0.95


Table 6.4 Default parameters for warehouse building areas

Zone Occupancy (m²/person)

Heat produced by equipment (W/m²)

Ventilation (ach/hr)

Lighting (lux)

HVAC

Office area 14.29 10 0.84 500 Radiator

Common room 9.09 5 0.1 150 Radiator

Enclosure 100 2 0.032 300 Air heating

Toilet area 9.09 5 1.58 100 Radiator

6.5.3 Results of thermal analyses A total of 216 analyses were carried out. Figure 6.10 presents the annual operational heating demand for medium sized buildings and Figure 6.11 for small buildings with varying orientation and rooflights for the base case, current, good, better and best practice.

Clearly, the location of a building has a considerable impact on the total heating demand which indicates lower heating demand in London compared to Berlin and Helsinki. It can be deduced from the results that building orientation (NS and EW) and roof lights percentage (12% and 20%) have very little impact on the total annual heating demands for the three locations. The impact of orientation and roof lights percentage would be higher if over-heating and cooling demand were considered in the analysis.

Overall, the results show that a considerable energy saving can be made when buildings are renovated. The best practice renovation option provides the highest energy savings. Nonetheless, the decision as to the level and scope of renovation (e.g. current, good, better or best practice) largely depends on the drivers for renovation, such as national regulatory requirements and acceptable level of return on investment in different countries. The empirical relationships for heating demand developed from this study were implemented in the Economic Justification Tool in Section 9.

0

1000

2000

3000

4000

5000

6000

7000

8000

12% rooflights 20% rooflights 12% rooflights 20% rooflights 12% rooflights 20% rooflights 12% rooflights 20% rooflights

NS EW NS NS

London Berlin Helsinki

60x120x10

MW

h

BaseCase Current Practice Good Practice Better Practice Best Practice

Figure 6.10 Annual energy demand for 60 m x 120 m x 10 m single storey warehouse


0

200

400

600

800

1000

1200

1400

1600

1800

12% rooflights 20% rooflights 12% rooflights 20% rooflights 12% rooflights 20% rooflights

NS NS NS

London Berlin Helsinki

30x60x6

MW

h

BaseCase Current Practice Good Practice Better Practice Best Practice

Figure 6.11 Annual energy demand for 30 m x 60 m x 6 m high single storey warehouse

6.6 Case studies on buildings before and after upgrading A number of existing buildings which underwent improvements to their building envelope were studied during the project; a selection of these studies is given below:

6.6.1 Case Study 1: Potters Place, Skelmersdale, UK

The building is a 1960's steel portal frame industrial building. The total building area is about 10,000 m2 and it is currently unused. It consists of a central shop floor area with office accommodation and other service areas such as toilets, plant room and common room at the periphery.

The existing envelope was generally in a poor condition, as shown in Figure 6.12. The existing roof was made up of mineral wool insulation sandwiched between asbestos cement sheeting and internal fibre boarding. Roof lights are single skin plastic. Lower level walls are uninsulated cavity brickwork. On top of the dwarf wall is a built-up cladding system with mineral wool insulation sandwiched between two corrugated asbestos sheets. In both roof and wall, sections of insulation were either missing or damp and wet. There were a variety of single glazed metal windows and galvanised roller shutter doors.

General description of the refurbishment work

Refurbishment involved removal of the existing asbestos sheet cladding to walls and roof. A built-up roofing and walling system (Platinum from Corus Panel and Profiles) incorporating triple glazed roof lights was installed. Entrance screens and windows were replaced with double glazed powder coated aluminium frames and insulated lath roller shutters. Existing dwarf wall (cavity brick walls) and ground-bearing concrete floor slabs were made good and painted. All existing HVAC was replaced and basic electric panel heaters were installed in the toilet, office and kitchen area. No heating or ventilation was installed in the main enclosures, as this was left to the tenants as part of their fit-out works.


Front view

Side view

Figure 6.12 External view of Potters Place before renovation

Air-tightness and thermography tests

All broken window glazing and missing roof lights were replaced before the tests to enable a realistic measurement of the air leakage performance of the building to be taken. Furthermore all mechanical ventilation openings (excluding smoke extraction fans or openings) were sealed with polythene sheet and self-adhesive tape in preparation for the test. The tests were carried out in accordance with Method B – Test of the Building Envelope in EN 13829 [18]; the thermography survey was in accordance with EN 13187 [19].

The fan system consisted of two high capacity petrol-driven trailer fans sealed into the roller shutter doors on the rear elevation, as shown in Figure 6.13. These fans have a volume flow rate between 2.5 - 33 m3/s. The size of the fan was established in accordance with ATTMA TS1 [20], which states that the fan must be capable of achieving at least 80 % of the required air volume flow rate at 50 Pa pressure difference.

Figure 6.13 Installation of fans for air-tightness test

The approximate air permeability of the building was calculated to be q50 = 27.04 m3/(h.m2) (for 50 Pa differential pressure), i.e. the building is extremely leaky! The test result is consistent with the aggregated results from the Building Sciences Ltd’s Database of past tests for such buildings, which revealed that air permeability values of existing industrial sheds built between 1960 and 1970 ranges from q50 = 25 to 30 m3/h.m2 [21]. This is considerably higher than the UK air-tightness maximum requirement of q50 = 10 m3/h.m2 (and best practice value of q50 = 2 m3/h.m2).

A thermography survey was carried out during the air pressurisation test to take advantage of the combination of natural heat loss and artificially induced internal positive pressure from the fans, which led to increased external infiltration.


After renovation

The building has undergone a total refurbishment including a removal of all existing asbestos sheet cladding to walls and roof. The building has been re-clad with a built-up roofing and cladding system incorporating triple glazed roof lights, as illustrated in Figure 6.14. The entrance door and windows are replaced with double glazed units and insulated lath roller shutters. Table 6.5 summarises the various renovated parts of the building.

Front view Internal view

Figure 6.14 Model of Potters Place after renovation

Table 6.5 Renovation or replacement of construction elements

Construction Construction Element

Before Renovation After Renovation

Ground Floor Uninsulated cast concrete Uninsulated cast concrete

External Dwarf Wall Uninsulated Brick and Block wall Uninsulated Brick and Block wall

External Wall Cladding Asbestos cement sheet, cavity, steel sheet

Built-up steel cladding system

Internal Wall Brickwork wall with plaster both sides Brickwork wall with plaster both sides

Internal Floor Cast concrete Cast concrete

Roof Asbestos cement sheet, cavity, steel sheet

Built-up steel cladding system

Personnel Door Steel, cavity, steel door Insulated steel faced door

Vehicle Door Aluminium skin Insulated aluminium faced door

External Glazing Single glazed, steel frame Double glazed unit

Rooflights Single polycarbonate sheet Triple layer polycarbonate sheet

Parameters for thermal analysis of Potters Place

Table 6.6 presents the key parameters used in a thermal analysis of Potters Place. The assumed parameters for occupancy, equipment, ventilation, lighting and HVAC are in Table 6.4. The building is assumed to be naturally ventilated.


Table 6.6 Parameters for thermal analyses of industrial building

No Base Case After Renovation

1 Air-tightness m3/(h.m2)@50 Pa 27 10 Cavity wall 1.7 1.7 Wall panel 2.3 0.35 Internal wall 1.0 1.0 Roof 1.95 0.25 Grd floor 1.0 1.0 Window 6.3 2.20 Rooflight 6.3 2.20 Solar shading (effective g-value) 0.85 0.56 Entrance door 3.0 1.60

2 U-value (W/m2K)

Vehicle access door 5.7 1.50

% 20 20

% 15 -----

3 Roof lights Area

% 10 ----- Gutter (Valley) 2.2 1.50 Drip (wall ground fl.) 1.15 1.15 Roof –wall (Eaves + Verges) 0.60 0.60 Wall – corner wall 0.25 0.25 Wall – floor not grd. 0.07 0.07 Lintel (window/door) 1.27 1.27 Sill below window 1.27 1.27

4 Thermal bridge values (W/mK)

Jamb (window/door) 1.27 1.27

The thermal simulation was carried out using the Simplified Building Energy Model (SBEM) [22], the UK national approved tool. The building was divided into four zones (shed, office, common room and toilet) for the analysis. Sensitivity analyses on the contribution of key parameters to the overall thermal performance of the base case building were investigated. The analysis consisted of the following:

Base case (before renovation of the building)

Locations (North, Midlands, West and South of the UK)

Air permeability of the whole building (27, 10 and 7 m³/h.m2 @ 50 Pa)

Variation in the U-values of the building envelope

Percentage of roof lights area (20%, 15% and 10%)

Thermally efficient details

Energy efficient lighting

The sequence of analysis can be broadly grouped into two stages as discussed below:

Firstly, the ‘Before renovation’ compared with ‘Target’ were analysed using the location of the case study building (Manchester). The base case represents the ‘Before renovation’ while ‘Target’ represents the expected ‘After renovation’ whole building thermal performance to comply with the UK Building Regulations [23].

Secondly, the locations were changed to consider other locations in the UK such as Glasgow and London.

The results of these analyses are presented in Table 6.7.


Table 6.7 Results of thermal simulations using various weather data sets in the UK

Predicted energy use kWh/m2/yr

Cases Space heating

Auxiliary energy

Lighting Domestic hot water

Total

Base Case 240.41 0.52 46.47 0.84 288.24

Notional building1) 38.33 2.71 50.95 0.94 92.93

Man

ches

ter

Target2) 29.32 2.07 38.98 0.72 71.09

Base Case 307.29 0.52 46.47 0.84 355.13

Notional building 51.13 271 50.95 0.94 105.74

Gla

sgow

Target 39.11 2.07 38.98 0.72 80.89

Base Case 195.64 0.52 46.47 0.84 243.48

Notional building 30.87 2.71 50.95 0.94 85.47

LOC

AT

ION

Lond

on

Target 23.62 2.07 38.98 0.72 65.38

NOTES:

1) Notional building (Cnotional) is defined as a building meeting the 2002 UK Building Regulations requirements

2) Target = Cnotional (1-improvement factor) (1 - LZC benchmark) where the improvement factor = 0.15 and LZC benchmark = 0.1 for heated and naturally ventilated (including buildings with low levels of heating). Hence Target = 0.765 Cnotional

Summary of findings

The following conclusions can be deduced from these analyses:

Total energy demand of buildings is linked to the location; south located buildings require less energy compared to north located buildings.

Total energy demand of a typical 1960s/70s industrial building “Before renovation” is in the region of 288 kWh/m2/yr. In order to meet the 2006 UK Building Regulations, the energy demand needs to be reduced by at least 75%.

The expected whole thermal performance “after renovation” needs to be lower than the Target energy demand of 71 kWh/m2/yr to achieve UK regulatory compliance.

Improvement in the whole building air-tightness from 27 down to 10 m3/h.m2 @50Pa accounts for 9% reduction in energy demand of the base case.

U-value improvement of roof elements has a higher impact (28%) on the energy demand compared to wall elements (5%).

Reduction of roof light areas has negligible impact on the energy demand.

When refurbishing buildings, roof cladding, roof lights and gutter U-values have the greatest impact on the whole building performance. These elements reduced the energy demand by 49% compared to “Before renovation”.

Low U-values, improved air-tightness, thermally improved detailing, low energy lighting and photoelectric sensors are imperative to reducing energy demand and CO2 emissions of the current building stock.


6.6.2 Case Study 2: Milton Keynes, UK

The report presents the outcome of air-tightness and smoke propagation tests carried out on two industrial sheds (units 2 - 4 and 16) in Milton Keynes, UK. Unit 2 – 4 is yet to be refurbished while Unit 16 is newly over-clad with a built-up roofing and cladding system.

Building description

The buildings tested were typical 1960s/70s large steel portal frame industrial buildings, with block walls dividing them into small units (double and single units). Unit 2 – 4 is a double unit and was tested “Before Renovation", while Unit 16 is a single unit and was tested “After Renovation”. The buildings were clad with dwarf brick cavity wall and asbestos cement sheet. On top of the dwarf wall was a single skin asbestos cement sheet. The roof consisted of a single asbestos cement sheet and a single glazed roof light, which runs along the centre of the roof and down on the north elevation. A series of single glazed windows run along the west side of the building. The floor is a ground bearing concrete slab.

Units 2-4 form a double unit with total floor area of about 1260 m2, and comprise a two storey rectangular shaped industrial unit with offices on the first floor and toilets and a large open plan warehouse facility on the ground floor (see Figure 6.15).


Figure 6.15 Milton Keynes case study, Units 2 – 4, before renovation

Unit 16 is a single unit with a total floor area of about 630 m2. The is effectively the same construction as Unit 2-4 except that it is half the size and the existing asbestos sheet cladding has been over-clad with mineral wool insulation and external steel liner attached to the existing envelope via steel brackets (Figure 6.16). Insulation thickness of 180 mm and 120 mm for roof and walls was used to comply with the current minimum UK Building Regulations (U-values of 0.25 and 0.35 W/m2K for the roof and wall respectively). The dwarf cavity brick walls were uninsulated.


Figure 6.16 Milton Keynes case study, Unit 16, after renovation


Air-tightness test results

The air permeability of Units 2-4 was calculated as q50 = 27.58 m³/(m²h) (for 50 Pa differential pressure), whereas for Unit 16 it was calculated as q50 = 26.36 m³/(m²h) (50 Pa differential pressure), which is considerably higher than the requirements for new buildings (< 10 m3/m2/hr) and only slightly lower than the similar building before renovation.

In Unit 16 no leakage was observed from the eaves, corner, service penetration, steel laps and end joint interfaces. However, it was noted that the smoke from the internal enclosure leaked through the internal envelope and travelled behind the new steel cladding. This then found its way out through the joints between windows to cladding, doors to cladding and steel cladding to brick wall interfaces.

The following leakage paths were identified through the building envelope:

Ridge roof light

Window glass louver

Window/door head

Window sill

Under roller shutter

Steel cladding to brick

Roof lights to cladding

Window/door jamb

Current practice of over-cladding existing buildings did not seem to achieve acceptable results. Under normal circumstance, the air-tightness membrane is best placed on the internal face of the building envelope. Previous laboratory tests and physical tests on new buildings have shown that steel clad buildings are capable of achieving air-tightness value of less than 3 m3/h.m2 @50 Pa when the internal steel liner joints are well sealed to serve as an air-tight membrane. The use of external cladding as an air-tight barrier for refurbishment of existing buildings is not effective on its own. Therefore, there is an urgent need to re-think the design detailing for over-cladding existing industrial-type buildings.

Based on these findings, it is therefore strongly recommended that a separate air-tight membrane be introduced directly on the external surface of the existing cladding before insulation and new over- cladding are installed. This air-tight membrane needs to be a breathable membrane (vapour permeable layer) to allow moisture movement through the envelope and avoid condensation risk, and at the same time prevent air leakage in line with current building regulations.

6.6.3 Case Study 3: "L" assembly buildings, Poland The ME&A Faculty (so called “L” assembly) of Rzeszow University of Technology consists of five connected buildings and one separate building (Laboratory of Combustion Engines). These buildings, designed over 25 years ago, have 3 and 5 storeys, with aluminium and glass façades. Due to significant thermal problems in winter, the University authorities decided to renovate the buildings. The construction of the external walls before refurbishment of the first and higher floors in the building assembly “L” is given in Table 6.8.

Table 6.8 External wall construction of Building assembly “L”

Thickness Thermal conductivity

Density Heat resistance Material

d [mm] [W/m2K] [kg/m3] R=d/ [m2K/W]

1 Gypsum-plasterboard 10 0.23 1000 0.043

2 Mineral wool (inside walls) 70 0.043 60 1.628

3 Aluminium 5 200 2700 ~ 0.000

A heat transfer coefficient for the external walls in the “L” assembly buildings was taken as U = 0.543 W/m2K. This value corresponds to a specific annual energy demand of approximately 200 kWh/m2a for this location in Poland.

Based on how cold the buildings were during the winter, it was presumed that the mineral wool had slipped down inside the frame walls. IR images confirmed this to be the case (Figure 6.17).


Figure 6.17 IR image and photo of tested walls of the “L” buildings (before renovation)

Analysing the walls after improving the insulation showed that large areas of heat loss still occurred through the façade, for example through the old windows, which had not been changed during this first phase of renovation. The maximum temperature on the wall (directly indicated in Figure 6.17) is equal to 0°C, for an external temperature of – 6.1°C. The relatively high temperatures on the windows located on the south side of the building were due to solar radiation, which took place a couple of hours before measurement.

During renovation, it was confirmed that the mineral wool had fallen down inside the frame. The new insulation, based on a 200 mm mineral wool layer (previously the thickness was 70 mm) has improved the thermal performance of the walls up to a U value of 0.333 W/m²K. Figure 6.18 shows IR images after renovation.

Figure 6.18 IR image and photo of the “L” buildings (after renovation)

6.6.4 Case Study 4: Aircraft production hall, Poland The thermal performance of the roofs and the facades of a production hall of an aircraft company were investigated. The building is located in Glogow Malopolski, several kilometres from Rzeszow. It is quite old and currently in use. The production hall is made of a steel frame. The roof construction is trapezoidal steel sheeting covered with an insulation layer (mineral wool) and foil on the external face.

The IR image in Figure 6.19 shows a large temperature distribution across the roof. The foil joints and all connections are marked as black and the pink areas reveal the best insulated places. The rest of the roof area, because of poor insulation, had an average surface temperature of 26.7°C. The external temperature during the measurements was 9.0°C.


Figure 6.19 Production hall roof (Building B before renovation)

Figure 6.20 shows the roof building B after renovation. At an average external temperature of +10, the temperature on the roof surface is in the range of +9.7 to +10.4C.

Figure 6.20 Production hall walls (Building B, after renovation)

6.6.5 Case Study 5: Sports hall, Germany

A sports hall from the early 1970s, mainly made of aerated concrete elements, needed renovation. Over-cladding using steel sandwich panels was chosen. An important additional benefit of this solution is that the wind load on the existing façade can be reduced as the composite panels are able to transfer the loads laterally to the columns. Figure 6.21 shows the building before and after renovation (though with the windows still missing).

Figure 6.21 Sports hall (left: before renovation, right: after renovation, not fully completed)

IR surveys were carried out before the renovation. An air-tightness test was also attempted but it failed because the building was so leaky! After renovation, IR surveys and an air-tightness test were performed again. The air-tightness test demonstrated good air-tightness with an n50-value of 0.63 h-1 (Figure 6.22). This is significantly below German requirements (1.5 h-1), and nearly at the level of a Passive House standard (0.6 h-1).


100908070605040302010

25000

20000

15000

10000

5000

pressure difference [pa]

Air

flo

w [

m³/

h]

depressurisation

pressurisation

Figure 6.22 Air-tightness test, using three fans (left), result (right)

The IR images show that typical details (foundation, parapet) are quite good (Figure 6.23). Although the overall performance and various details are good, the combination of air-tightness tests and IR surveys identified some weak points, for example there are leakages at the junctions of vertical facades and the reveals (Figure 6.24).

Figure 6.23 IR image after renovation (ambient temp.: -3 °C, indoor: 23 °C)

Figure 6.24 IR image after renovation (ambient temp.: -3 °C, indoor: 23 °C)

6.7 Design guidance on over-roofing and over-cladding There are many single storey buildings using metallic or other single skin cladding systems that require over-roofing to improve their weather-tightness, appearance and thermal performance. For many of these industrial buildings, a long interruption of the production process is not possible, and so over-roofing whilst preserving the original roof is very cost effective. The building owners of industrial buildings mostly accept only very short payback periods as the (projected) life-time is typically 30 years. Furthermore, the cost of refurbishment of the building has to be balanced against investments for improving machinery and processes, which is normally the main interest of a


company. In consequence, technical solutions for over-roofing and over-cladding with low capital costs are needed, which are reviewed below as follows:

6.7.1 Over-cladding of single storey buildings Steel sandwich panels: For application on concrete or blockwork walls, steel sandwich panels may be used and additional steel profiles for fixing and adjustment of the panels are required. The achievable level of thermal insulation is determined by the thickness and properties of the sandwich elements, and a U-value of 0.15 W/m²K is possible.

Figure 6.25 Concrete wall, refurbished with steel sandwich panels

Cassette or built-up walls: The heat transfer through cassette walls that are built-up on site is strongly related to the thermal bridging effect. Therefore, additional thermal insulation has to be provided to overcome the effect of these thermally weak points. If the external cladding is removed, two options can be adopted a) additional insulation and covering by trapezoidal sheet (Figure 6.26, left) or b) adding a steel sandwich panel externally (Figure 6.26, right). Depending on the materials of the original wall and the additional insulation, U-Values of less than 0.25 W/m²K can be achieved.

Figure 6.26 Over-cladding using a cassette wall or sandwich panel (left and right respectively)

6.7.2 Over- roofing of single storey buildings

For over-roofing of single storey buildings, self-supporting elements such as steel sandwich panels are an option for many cases (see Figure 6.27, left). In this case, new purlins may be required, especially if the existing purlins have deteriorated or are not able to support the additional loading. The existing envelope is retained below the new cladding, and so the use of the building is not affected. A built-up over-roofing system may also be used (see Figure 6.27, right). The brackets supporting new built-up system are attached to the existing purlins and the new insulation and roof sheeting is fixed conventionally. In both cases, a high level of thermal insulation can be provided, although thermal bridges exist at the horizontal rails and connection points.


Figure 6.27 Over-roofing using composite panels (left) and built-up roofing system (right)

6.7.3 Design requirements for over-roofing and over-cladding of single storey buildings

The following design requirements are relevant to over-roofing and over-cladding:

Structural resistance: The new cladding systems and its support structure must be designed to resist the additional self weight loads due to the new cladding and services attached to the roof, and any additional wind loads calculated to modern Codes. The local wind pressures may also be affected by any change of roof shape after renovation, and is also likely that design to EN 1991-1-424 will lead to higher local pressures than to former Codes.

Thermal insulation: The energy use of a typical single storey industrial building to modern standards will consume only about 20% of the energy use of a building to 1970s standards. A U-value improvement of roof elements has a higher impact (28%) on the total energy demand compared to wall elements (5%). The impact of roof light areas on the energy demand due to their heat loss relative to the insulated roof is offset by the savings in electricity use by effective day-lighting and additional solar gain.

The level of thermal insulation that is provided depends on the thickness of the sandwich panel or the mineral wool insulation placed between the rails, as shown in Figure 6.27. A 100mm deep sandwich panel can achieve a U-value of 0.2 W/m2K, but 200 mm of mineral wool is required to achieve the same U-value. In addition, thermal bridging will occur through the rails and brackets in the built-up system, which can add 10% to the heat loss that should be taken into account.

Air-tightness of over-roofing and over-cladding systems: Ventilation losses (cold air infiltration) can occur if the air-tightness of the new building envelope is not improved significantly. Improvement in the whole building air-tightness from 27 to 10 m3/h.m2@50Pa accounts for 9% reduction in energy demand of the base case.

The air tightness tests carried out in this research showed that over-roofing using built-up roofing and cladding systems are frequently not very air-tight because of the many junctions in the roof system, such as at the roof to wall junction, at roof lights and at the ridge and end gables. Sandwich panels are more air-tight than built-up systems.

Guidance on achieving a high level of air-tightness in the renovation of single storey buildings is presented in Section 6.4.4. The importance of effective seals around the points of potential air leakage is emphasised in this best practice guidance.


7 WP3: STEEL INTENSIVE TECHNOLOGIES FOR BUILDING EXTENSIONS


7.1 Objectives In many European cities, the lack of available land means that there is pressure to extend and adapt buildings to meet new social and economic demands. This part of the project addressed the technical aspects of the following types of renovation using steel technologies:

Structural extensions, both vertical and horizontal.

Conversions of use.

Vertical or roof-top extensions pose particular questions which require an understanding of the structural capabilities of the existing building and of the connection between the new and existing structure. Investigations on buildability, safety and construction issues are also addressed. The specific technical and economic requirements of each building sector have to be taken into consideration.

7.2 Review of recent experience A review of recent experience in Europe was carried out, covering building extensions in residential, commercial, office and industrial buildings. For the majority of projects, renovation consists of keeping an essential part of a building (frame, main façade, etc) whilst modifying it to resist the additional loading. Examples of building extensions using steel technologies are shown in Figure 7.1 and Figure 7.2.

Over roofing and over-cladding of an existing 4 storey residential building in Denmark

Roof top extension of a project in Rotterdam

Figure 7.1 Vertical extensions in residential buildings

The terms ‘major’ or ‘light’ can be used to denote extensive or superficial renovation work. Renovation often means an improvement in the comfort, safety, or aesthetics, in which case the works are termed ‘light’. For cases involving structural intervention, renovation is termed ‘major’ or extensive.


Extensions can be horizontal or vertical to the existing building. The starting situation depends on several factors:

The use of the existing building: residential, commercial, public building, etc.

The location of the building: city centre, suburb, or in the countryside.

The quality of building: such as the state of the materials, and aspects such as its thermal and acoustic insulation.

Extension for Industrial workshops - Public company of transport, close to Paris

2 and 3 storey extension of Rzeszow University of Technology, Poland

Figure 7.2 Vertical extension in industrial and office buildings

Conversion often involves a ‘change of use’. By converting offices to residential use, loads and conditions are modified and new thermal efficiency, fire safety, health and other requirements are introduced. Table 7.1 presents a summary of the drivers for building extension or conversion projects and presents the criteria and the Regulations to which they are linked.

Vertical extensions are most common and more technically challenging than horizontal extensions and may involve over-roofing as well as creating a new habitable space. Horizontal extensions may include balconies, lifts and stairs.

The first stage to designing an extension involves an estimation of the load-carrying capacity of the existing building. The speed of construction and lightness of the new structure are two major advantages of steel solutions. Additionally, steel solutions are able to span between strong points on the existing roof.

Table 7.1 Drivers for renovation by building extensions

Drivers for Renovation by Building Extensions

Main criteria for first decision Related to a standard or regulation

Roof-top extensions to create more space Load capacity of the existing building Structural and thermal

Building extension Suitable space Urban planning

Change of use (building) Economic All (but not directly)

Energy efficiency improvements Economic incentives or change of use Thermal regulation

Upgrade to new regulations Energy / Fire Safety Thermal / fire safety Regulation

New lifts, stairs, balconies Economics and improved facilities Urban planning

Conservation of national heritage register Aesthetics, such as façade All (but not directly)

Deterioration of existing building Strengthening or arresting deterioration Structural


7.3 Investigation of buildability and technical issues The purpose of a feasibility study is to provide a basis for the investor to decide whether a project is feasible. In addition to the economic aspects, the main topics to be studied are:

The regulations of town planning and special points about aesthetics and visual integration

The characteristics of the existing building

Technical issues such as structure, thermal insulation and fire safety.

This research was primarily focussed on requirements for vertical extensions, because this includes additional loads applied to the existing structure, influences on fire safety and different aspects of urban and architectural integration.

Local legislation and regulations are of great importance for any building extension project. An overview of the different national regulations highlights certain local differences. However, the following relevant points generally have to be considered:

Local plans may impose limitations on aesthetics, height, shape of roofs, as well as type of use,

Height is also connected to the natural lighting issue. The geometrical arrangement of the new building has to preserve natural light for the neighbours,

The building can be registered as an historical site. In this case, the project has to take into account the constraints on the appearance of the façades and the roof,

The additional building density may require new columns.

The characteristics of the existing building have an important bearing on the choice of structural solution to adopt for an extension. A study was carried out to collect information for European countries on the ‘most common’ dimensions of the building and the essential requirements of the main regulations covering structural design, fire safety, thermal regulation etc.

A database of typical characteristics of existing residential buildings has been established, and is presented in Table 7.2.

A case study based on a vertical extension project has been investigated in detail. It is a 3 storey building and the study considered the addition of two types of roof. In this model (Figure 7.3), 8 key-points were identified as potentially critical with respect to requiring special interface requirements:

1. Base of column (structure) and external skin (façade) between the old and new buildings

2. Interface between a new slope roof and an existing part (vertical or horizontal)

3. Connection to a new balcony

4. Interface between a flat roof and an existing wall

4. Also, between a new slope roof and an existing part (vertical or horizontal)

5. Vertical and horizontal interfaces along the connected building

6. All types of joints as expansion or movement joint

7/8. Typical shapes: angles for envelope and positions of bracing for structure,

The first step in the assessment dealt with existing load-bearing elements (type of materials, structural elements and functions); the second step was a study of the characteristics of supports (age and quality, requirement for the new design), and finally the influence of modern regulations was considered.


Table 7.2 Typical dimensional characteristics of residential buildings

Typical Dimensional Planning Criteria

Relevant Dimensional Factor Unit Most common Low limit High limit

Floor to floor height m 2.7 – 2.8 2.5 3

Internal room height m 2.4 2.3 2.7

Houses storeys 2 1 3 Typical number of floors Residential storeys 4-6 (lift n > 4 storey) 3 8

Houses mm 200 120 300 Floor depth

Residential mm 400 350 500

House m 8.5 ? 10 Depth of building Residential m 12 - 13 10 17

House m 3.3 - 4.5 3 5 Floor spans

Residential m 4.2 - 5 3 75

Typical size (L W) L W 5 2.3 4.8 2.3 5 2.5

Disabled user L W 5 3.6 4.8 3.6 5 3.6

Secondary support to façade m 0.6 0.6 0.9

Planning dimensions m 0.6 0.3 1.2

Flat roof for multi-storey ° 0 0 5 Roof Shapes

Slope ° 35 – 40 15 50

1

2

3 4

5

67 & 8

3- storey existing building

Jointed building

Figure 7.3 Case study of a vertical extension: typical scheme showing key interfaces

7.4 Connecting a vertical extension to an existing building The connections between steel and other materials at the interface of the vertical extensions and the existing building are very important. For the structural frame, the following aspects have to be assessed in order to appraise the best way of connecting the new extension to the existing building. At the interface, new loadings have to be supported, as follows:

new horizontal loading: wind applied to the extended building and also calculated to new Codes,

new vertical loading: dead weight, variable loading, local loads, service loads, cladding loads etc.


7.4.1 Steel column to concrete wall (point connection)

Figure 7.4 defines various cases where a new column is supported by an existing concrete wall or a column. In the case of a parapet in Figure 7.4(a), even with a pinned connection, the loading at the base of the parapet will be vertical load, shear load and moment which can be relatively significant in a weak area of the parapet that is potentially weakened by long term weathering. Moreover for a fixed connection, the applied moment will also be relatively high.

In the case of a simple external wall in Figure 7.4(b), the structural zone is also more rigid due to the horizontal slab, beam, and a fixed connection can be developed taking account of the slab rigidity. In the case of “middle of the slab” in Figure 7.4(c), the balance of moment between the left side and right side of the spans at the support will lead to balanced moment and a low moment acting on the connection. This case is also applicable at the intermediate support of a double span portal frame.

Figure 7.4 Several types of connection: column to concrete wall

The following connection types may be considered:

Pinned connection: Two anchors or reinforcing bars, connected if possible to the existing reinforcement, means that the connection is considered as pinned;

Fixed connection: Four anchors must be placed at a suitable distance apart to develop sufficiently high moment in order for the connection to be considered as ‘fixed’. The end plate thickness should be compatible with the forces exerted by the anchors acting in tension.

For a 200 mm concrete wall, a minimum cover of 40 mm to the external reinforcing bars or anchors should be considered, which means that the distance between them can be as little as 100 mm. In this case, it is not practical to resist significant moment and a thicker wall is required.

Transversal Wall

Figure 7.5 (a) Pinned connection and (b) fixed connection

1. Steel column, 3. Connection plate, 4. Anchor, 5. Wedge

Use of slotted holes permits adjustment for large tolerances in one direction. This will require the use of specific washers to be designed for bending and shear.

parapet


An investigation was made of 3 different types of connections, based on the degree of fixity required, as illustrated in Figure 7.6 below:

Figure 7.6 Concrete/steel connection: Frictional, end plate, anchors

Guidance on anchors is given in CEN/TS 1992-4-2:2009 [25]. Post-installed anchors can be of several types such as expansion anchors, undercut anchors, concrete screws, bonded anchors, bonded expansion anchors and bonded undercut anchors, as illustrated Figure 7.7. The most efficient connection devices are adhesive (chemical or mechanical) anchors.

Figure 7.7 Post-installed fasteners types


7.4.2 Pre-design study for steel portal frame connection to concrete wall

A common design solution for roof-top extensions is a steel portal frame or similar moment-resisting structure. A pre-design study was carried out for a 30 m 12 m horizontal area to be extended. The structure is made from a basic frame model, 3 m high and 12 m longitudinal span. The transverse span between two adjacent frames is taken as either 3 or 6 m. The combination of parametric factors leads to 24 design cases, as summarized below.

The loads considered (all to be multiplied by partial safety factors) are:

Dead weight: 4.2 kN/m² including a 150 mm concrete slab

Live loading: 1.5 kN/m² (residential)

Wind loading: 1 kN/m²

Snow loading: 0.45 to 0.8 kN/m².

LEVEL (S) = (3 cases) 1, 2 or 3 level extensions

ROOF (of existing) = (2 cases) The existing roof supports the floor loads or a new floor is created

CONNECTIONS = (2 cases) Pinned or rigid connection between elements

Longitudinal span made of single frame or two bay frames with one intermediate column (2 cases)

The predicted range of moments acting on the beam-column connections for the case of rigid connections was calculated as:

21 kNm/m for one new level consisting of 2 6 m spans

62 kNm/m for one level of a single 12 m span

43 kNm/m, for 3 level extensions of 2 6 m spans

12 kNm/m for 3 levels of a single 12 m span.

From this parametric study, assuming transverse spans of 3 m and 6 m, it was shown that suitable steel sections range from HEA100 to HEA240.

7.4.3 Light steel wall to concrete wall (continuous connection)

If the existing structure is made of masonry walls, the roof-top extension should be constructed from light steel framed wall panels. To connect these panels to the existing wall, a continuous connection in the form of a U-track is required. The U track is fixed into the wall by expansion fixings normally placed every 600 mm, as illustrated in Figure 7.8.

Figure 7.9 shows anchorage to a precast concrete slab. The shear and tension loads are in most cases less than 10 kN/m. The proposed anchors are in stainless steel, although galvanized fasteners are also possible, depending on the exposure condition of the renovated structure.


Figure 7.8 Point connection for continuous connection on a concrete walls

Figure 7.9 Anchorage of the lower U-track in the compression slab

A study was carried out to design the connections between a vertical extension made of light steel wall panels and an existing building with concrete walls for two theoretical buildings.

7.5 Safety and access issues Fire regulations play an important role in the design decisions regarding building extension or conversion. The following issues should be addressed:

Escape routes from the new apartments: depending on regulations and the height of the building.

Escape routes from the apartment in the existing building. The stairways should be designed for the extra floor or an external shaft has to be added.

The fire resistance required for the doors of the apartment could change.

The structural roof/floor between the existing building and the new ‘attic’ floor has to be fire resistant.

The fire load characteristics of the new envelope must reduce the risk of fire propagation.

If the new ‘attic floor’ cannot be reached by ladders by the fire brigade, some special arrangement should be established to assist fire fighting.

Installation of an elevator may be required with the addition of only one new level (depending on the local regulation, but is required for access to the fourth or fifth floor from the ground).

Creation of new parking spaces is required by many urban projects. This may require some work at basement level or creation of a ‘podium level’ for parking below.


7.6 Investigation of semi-rigid corner joint characteristics A study was carried out to determine semi-rigid corner joint characteristics of bolted lap joints used in thin walled steel structures; these characteristics can then be used in a global analysis of a structure.

7.6.1 Test arrangement

Figure 7.10 shows a typical bolted lap joint in a cold-formed steel frame. This type of joint is generally considered as pinned, which increases the bending moment in the beams. In fact, such connections are ‘semi-rigid’. However, their moment-rotation (M-) characteristics can be effectively predicted only by experimental testing, which is costly. Numerical simulations offer an alternative method to obtain the flexibility parameters of such joints. The simulations can be carried out using FEM software.

Tests were performed at the University of Rzeszow laboratory and compared to a numerical FEM model. The tests were used to calibrate a mechanical model. The test specimens were fabricated from galvanized cold-formed steel profiles. Two types of arrangement of the specimens were analysed. In the test 1, a specimen was connected to a rigid frame by the column only and in test 2, the base of column was connected, and the tip of the cantilevered beam has a fixed degree of freedom in the horizontal (in plane) direction (Figure 7.10).

Figure 7.10 Connection under study with laboratory set up: Left: test 1 and right: test 2


7.6.2 Numerical simulations

The main aims of the numerical simulations were to obtain the moment–rotation (M-) curve and use the results from the experimental tests to calibrate the numerical model.

Figure 7.11 shows the geometrical model used to obtain the flexibility parameters of the bolted lap joints using numerical simulations; the finite element programme was ADINA. Five contact surface models elements were introduced into the model, i.e., between the:

beam and gusset plate.

column and gusset plate.

beam and bolts.

column and bolts.

gusset plate and bolts.

Figure 7.11 Numerical model of the connection

7.6.3 Moment-rotation characteristics

The proposed mechanical model for the frame and its connections is presented in Figure 7.12 alongside the measured moment-rotation curves. Based on the results of the analysis, it was concluded that the first method of attachment of the specimen to the rigid frame (test 1) should not be used in future experimental tests. The results obtained using the second method attachment (test 2) correspond with the behaviour of the joint in the structure, and this type of test should be used in future experimental tests. The analysed beam column connection can be classified as a ‘semi-rigid’.

The failure modes are illustrated in Figure 7.13.


k 1

k 2k 3

Sj,ini

P P

Figure 7.12 Moment-rotation curve for connection

a) b) c)

failure of gusset plate ovalisation of bolt holes

Figure 7.13 View of failed elements (test 2)

7.7 Tests on the connection between a steel frame and existing concrete wall

7.7.1 Test arrangement

In order to validate the expected behaviour of the connection between a new steel frame and the existing building structure, a series of tests was carried out at the University of Rzeszow. The test arrangement includes a concrete wall base of 200 mm thickness simulating the existing building frame (assumed to be a residential building made of concrete wall panels). A steel portal frame was connected to the top of the concrete wall.

Two types of tests were performed:

1. One test as a pure ‘pinned’ connection with shear loads acting on the wall only

2. One test as a ‘semi-rigid’ or a fixed connection to a transverse wall perpendicular to the concrete wall (as expected on the existing building).


Figure 7.14 shows the test details. One test was carried out with an HEA section column, which is treated as pinned and the other test with an IPE section, which is treated as semi-rigid. The figure also shows the portal frame resting on the concrete wall, and the concrete wall resting on the concrete base. The frame was reduced in size, compared to the building arrangement to fit with the laboratory floor fixing system. The loading arrangement is shown in Figure 7.15.

Test disposition for HEA200 sectionx'

Test disposition for semi-rigid section

Transversal wall

R bars axes : d=120mm12

20 Wall thickness : d=200mm

Exte

rnal

wal

l

x

3m

H

NN

0.2m Concrete wall0.8 - 1m high.

Concrete base.

Enchor concrete blocs baseinto laboratory floor.

Laboratory floor.

Beam transversally restrained.

Figure 7.14 The test arrangement

Chemical anchors were chosen because of the small edge distance. The design resistance was established for plain concrete without reinforcement. The concrete grade was chosen to be representative of existing concrete with a grade not exceeding C16.

7.7.2 Test results

The main results obtained from the tests for pinned connection are presented in Figure 7.16 in terms of the relationship between horizontal load H and the horizontal displacement of the upper beam of the steel frame, the moment-rotation at the connection, and the relationship between the horizontal load H and concrete wall displacement at the connection. The test was discontinued at a shear load of 100 kN, which is considerably in excess of the horizontal wind loads that would be expected in a one or two storey extension. The movement of the concrete wall was 4.5 mm at this load and the displacement of the frame was approximately 50 mm. The moment diagram at a shear load of 100 kN is also given. It is apparent that a small moment is generated at the base of the frame, even if designed as pinned.


Figure 7.15 Arrangement for the test rig frame

0

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120

0 10 20 30 40 50 60

H [kN]

gl [mm]

H‐gl

‐5

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M [kN

m]

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connect‐left

connect‐right

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‐0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0

H [kN]

c [mm]

H‐c

c‐L

c‐R

Figure 7.16 Results for pinned portal frame test


The main results obtained from the tests on the fixed connection are presented in Figure 7.17, in the same form as for the pinned connection. These tests were continued to a shear load of 160 kN, at which point the horizontal displacement of the frame was 60 mm. At a load of 100 kN , the displacement was 60% of that of the pinned test. The bending moment diagram at this load shows that the moment in the column was reduced by 30% and the moment at the base was 60% of that in the frame, which indicated a high degree of base fixity (although not fully fixed).

‐20

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m]

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connect‐left

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160

180

‐0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0

H [kN]

c [mm]

H‐c

c‐L

c‐R

Figure 7.17 Results for fixed portal frame test

Note that there is a large difference between distribution of moment between the pinned (14.1 kNm) and fixed connection (45.6 kNm) cases. The failure mode was in the concrete by crushing of the concrete on the compression side, together with cracking of concrete wall on the tension side, as illustrated in Figure 7.18.

Figure 7.18 Failure modes in concrete base


7.7.3 Tests on light steel wall panel with single boards

Tests were also carried out on light steel wall panels subject to shear. The main objective was to obtain semi-rigid characteristics of the panel under horizontal loading and to estimate the stiffness of the panel, which can be used later in a global analysis of the structure. The applied vertical load was 12.5 kN and takes account of the roof and the cladding loads only. At a shear load of 15 kN, the variation of displacement as a function of vertical load is presented as in Figure 7.21 and shows that the maximum displacement was only 3.5 mm. At a shear load at failure of 60 kN, the panel in-plane displacement was 35 mm.

Figure 7.19 Wall build-up and wall panel prior to test

1. Stand, 2. Loading beam, 3. Screws M12, 4. Wall 4800 2890, 5. Hinged joint at base of bar, 6. Steel bars, 7. Load transducer, 8. Compression system for wall, 9. Load system

Figure 7.20 Test set-up


(a) Variation of load versus horizontal deflection with applied vertical load

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0 5 10 15 20 25 30 35 40

Horizontal displ. [mm]

Ho

rizo

nta

l lo

ad

[kN

]

Fv=12,5[ kN]

(b) Variation of load versus horizontal deflection for vertical load of 12.5 kN

Figure 7.21 Load–horizontal displacement curves at the end posts

7.8 Design guidance for vertical extensions A design guidance document was prepared which described the objectives and drivers of vertical extensions and the sequence of stages required at the pre-design stage. Generic techniques of renovation with steel were outlined, with the advantages of using steel clearly explained.


8 WP4: LIGHT STEEL SYSTEMS TO UPGRADE ROOFS


8.1 Objectives This Work Package concerns the opportunities for light steel systems to provide new habitable space by retro-fitting existing timber roofs and addresses the related technical and building physics issues for residential and commercial buildings.

8.2 Investigation of buildability and practical aspects Some initial studies focused on current roof typologies, roof structural arrangements and refurbishment practices. The study also developed a generic conversion methodology to create habitable roof space. Opportunities for light steel solutions were highlighted.

Roof typologies in the UK

Traditionally, residential roof structures are constructed in timber and the methods of fixings are nails, screws and bolts. Roof shapes are either near flat or pitched. The majority of houses have pitched roofs and the sides of the roof are either designed as gable end or hipped [26]. Some examples of typical roof typologies are shown in Figure 8.1.

‘T’ Intersection roof with gable side

Overlaid hip roof with gable side

Hipped roof

Figure 8.1 Examples of roofs

The level of complexity of retro-fitting existing timber roofs to creating habitable roof depends on the type of roof structure, which is linked to the period when the building was built. Typical refurbishment solutions for the main roof structures, together with potential opportunities for the use of lightweight steel components, are summarised below:

Flat roofs conversion

Two typical refurbishment options are ‘Flat-to-pitched’ conversion and creation of a new ‘Room-in-roof’. A study was carried out on the many lightweight cold-formed steel solutions on the market for flat-to-pitched roof conversion. In terms of placement of new ‘room-in-roof’ structure, the use of timber ‘Attic Trussed Rafter’, either as 2D panel or 3D module lifted onto the existing flat roof is very popular. There are some lightweight cold-formed steel systems on the market but they are not as popular as timber solutions. There are major opportunities for prefabricated lightweight steel solutions, for example the Open Roof System, for this application.

Pitched roofs conversion

Over the years, more than one million roofs have been converted to create a room-in-the-roof. Availability of headroom is a major consideration when converting loft space. The majority of the existing roofs can provide the minimum of 2.3 m headroom height required to be suitable for conversion. Dormer windows are widely used to increase the width of the room. The three most common existing roof structures are shown in Figure 8.2.


Strutted purlins Trada trusses Trussed rafters

Figure 8.2 Common structural forms of timber roofs

The generic structural alterations to these roof types to create room-in-the-roof includes installation of:

New beams spanning from gable to gable/party wall to carry new floor load,

New floor joists between the existing joists,

Stud wall on top of the beam to support part of the roof,

New beams at the ridge level (or near the apex) spanning from gable to gable/party wall for long span rafters or large new dormer window (≥ 1.2 m) added,

Collars depending on the span of the rafters,

Removal of existing strutted, purlin or trussed internal members.

Figure 8.3 shows that hot rolled steel beams are the preferred option despite the difficulty in installing the beams. Sometimes the beam needs to be cut into 2 or 3 small beams, which are then bolted together. Considering that about three steel beams are generally required for a typical loft conversion, this makes the logistics of loft conversion very tedious. Therefore, there are opportunities for the use of lightweight cold-formed steel for this application.

Typical structural modifications to trussed rafters for habitable roof

Typical structural modifications to purlin roof with large dormer window

Figure 8.3 Typical structural modifications to roofs to create habitable space


8.3 Investigation of the Open Roof System

8.3.1 Introduction to the Open Roof System

The Open Roof System consists of two basic forms. The first form involves the use of steel and plywood compositely to create a ‘plyweb’ beam for modification of existing roof structures to create an habitable roof. The second form involves the use of cold-formed C or Z sections to create a room-in-the roof truss, as illustrated in Figure 8.4. The range of application of the Open Roof System is:

Spans of 6 to 10 m.

Spacing of 400 to 1200 mm, depending on the span of the tiling battens and plasterboard supports.

Roof slope of 30 to 45°.

Habitable space of 3.5 to 6 m width between the vertical members.

There is the potential for an extension of the technique called the ‘Collapsible Open Roof System’ uses cold-formed steel that can be installed by crane. The connections of the rafters to floor joists are articulated. A further option is a ‘Plyweb Open Roof System’. This option uses a plyweb composite section in which the connections between the rafters and floor joists are made rigid by plywood inserts. The plyweb beam consists of C section flanges and 12 mm plywood webs.

8.3.2 Structural design of the Open Roof System

The structural design of the Open Roof System at the ultimate limit state is based on a modified plastic analysis, but using the elastic bending resistance of the rafters and bottom chords, which act as the floor in the roof space. The design principles comply with Eurocode 3 for steel design. The design loads are based on open roof trusses at 600 mm centres. The elastic deflections and internal forces were analysed using the finite element program LUSAS. Table 8.1 gives a summary of the results of the analysis.

Table 8.1 Results from LUSAS analysis for 8 m span Open Roof truss

Analysis Output Rafter Bottom Chord Struts

Max. bending moment at ULS (factored loading) 3.8 kNm 4.9 kNm NA

Max. axial force at ULS (factored loading) 14 kN –1.0 kN 15 kN

Unity Factor to EN 1993-1-3 0.89 0.58 0.51

Deflection at working loads

– imposed load 5.5 mm 5.9 mm NA

– imposed load + dead loads 8.8 mm 6.5 mm NA

– Imposed load + dead loads + snow load 13.6 mm 11.0 mm NA

The deflected shape of the Open Roof truss under imposed and dead loads shows how the rafter provides support to the bottom chord (Figure 8.5). It can be seen that the effective points of support of the bottom chord are at the strut positions, leading to an effective span of (L-2a). The moments in the rafters are combined with compression acting in these members due to loads transferred from the vertical members.


Screw

A

Section A - A

600 - 900

Timbers cut out

Inserted plyweb bea

(a) New structural elements

(b) Small sections of 'plyweb' made into beam on-site

A

Existing rafter

Capping section

Capping C section

Plyweb beamSection of plyweb beam

1800 - 3600Screw fixed on site

New habitable space

New light steel C (as floor)supported

Angle support

Plyweb open roof

1250

4800 - 6000 1600

2400

100

100

Closed cell insulation board

M 12 bolt

18 mm chipboard

200 - 300

120 - 150

35 - 40°

Lightweight cold-formed steel open roof

Figure 8.4 Forms of Open Roof Systems


Figure 8.5 Deflection shape of an 8 m span open roof truss under imposed and dead load applied to the floor

The recommended minimum sizes of the C sections to create the room sizes for a minimum room height of 2.4 m are presented in Table 8.2. The optimum design of the Open Roof truss is for an 8 m span, which is appropriate for a typical 3 or 4 bedroom house. In all cases, the vertical and horizontal tie members use 100 1.6 mm or 1.2 mm C sections and connections are made using 12 or 16 mm diameter bolts located in pre-punched holes.

Table 8.2 Typical chord and rafter sizes for the Open Roof System

Member Sizes Span (m) Roof Slope

Room Width (between verticals

Bottom chord Rafter

Approximate Steel Weight

(kg/m2)

6 45º 3.6 m 150 1.2C 100 1.2C 16

8 40º 4.4 m 180 1.6C 125 1.6C 18

10 35º 6.0 m 250 2.0C 150 1.6 C 24

Steel weight is expressed as relative to the plan area of the roof

The same analyses may be repeated for other spans, but it is generally found that deflections of the bottom chord will control the selection of the member sizes. It is concluded that the Open Roof System using light steel C sections is a simple and viable technique for creating habitable space in a roof without changing its basic form.


8.4 Simulation of thermal performance of upgraded roofs Thermal analyses were performed on a selection of residential building types in order to illustrate the energy savings that can result from renovation. The external envelope of residential buildings is can be solid brick wall, insitu/precast concrete wall, cavity brick wall or timber frame construction. TRNSYS was used for the thermal analysis, which is a flexible tool designed to simulate the transient performance of thermal energy systems. This program calculates the energy flux in a building and the temperatures of rooms and components.

8.4.1 Definition of simulation models for residential buildings

The upgrading of roofs has various effects on the thermal and energetic behaviour of a building. Depending on the characteristic of the renovation and the use of the building, the following aspects have to be considered:

Heat transfer coefficient (U-value) of the construction before/after renovation (including control of thermal bridges)

Increasing compactness (additional floor space with only few additional surfaces of building envelope)

Control of over-heating (large surfaces exposed to solar irradiation combined with little mass)

Air permeability (difficulty in quantifying air permeability of the old and new roof structure)

Table 8.3 and Table 8.4 show the residential building types and scenarios which were analysed. Three different European locations were considered: Helsinki, Berlin and London. The main shortcoming of this analysis is that in practice the base case (see Table 8.4) differs for the different European locations because of building traditions and national requirements.

Table 8.3 Residential building types analysed

Dwelling Type Floor Area (m²) (1) Sketch

Detached bungalow 67 L = 10 m B = 6.7 m

Mid-terrace house 79 L = 5.0 m B = 7.9 m

Semi-detached house 89 L = 6.0 m B = 7.4 m

Detached house 104 L = 6.5 m B = 8.0 m

(1) CE189 (2006) “Refurbishing dwellings – a summary of best practice”, Carbon Trust, UK


Table 8.4 Data for thermal simulations

Base Case (before loft conversion)

Good practice (with loft

conversion)

Best practice (with loft conversion) Element Description

U-value (W/m2k)

Pitched roof Uninsulated timber roof 1.9 0.20 0.15

Loft floor Timber joists, minimal insulation 0.85 0.25 0.2

External wall Uninsulated solid block 2.1 0.30 0.15

First floor Uninsulated timber floor 3.0 0.25 0.2

Ground floor Uninsulated solid floor 0.45 – 0.7 0.25 0.2

Window Partly double glazed 3.5 2.0 0.7

Window area (%) Wooden frame window 12 -15% 12 -15% 12 -15%

Air-tightness m3/(hm2) @50Pa 15 10 3

8.4.2 Simulation results for residential building Figure 8.6 and Figure 8.7 show some details for the net heating energy demand (monthly values) for the semi detached house, including the heating of the converted roof space.

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Figure 8.6 Monthly heating energy demand, semi detached house, base case (left: whole building, right: energy demand caused by heat transmission through roof)

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Figure 8.7 Monthly heating energy demand of converted loft in a semi detached house (left: good practice, right: best practice)

The energy demand for the new habitable space in the roof is small and depends on the quality of the upgrading (‘good’ or ‘best’ practice). Additionally, the energy losses of the existing part of the building are reduced, thus the heating energy demand of the refurbished building with additional space is lower than of the base case with lower floor area (see Table 8.5) and the additional heating energy demand is negative.


Table 8.5 Annual heating energy demand for various design cases

Case kWh/m2a Helsinki Berlin London

heating energy demand 369.0 262.0 213.9 Base case

heat losses roof 37.3 26.5 21.8

heating demand loft 102.7 62.6 44.2

reduction old building -123.0 -87.5 -71.9 Converted roof –good practice

additional heating demand loft -20.3 -25.0 -27.7

heating demand loft 71.8 41.5 27.8

reduction old building -123.0 -87.5 -71.9 Converted roof – best practice

additional heating demand loft -51.1 -46.0 -44.1

Figure 8.8 and Figure 8.9 give the annual heating energy demand for the other building types.

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base case insulation loftonly (insulationtop floor, no useof pitched roof)

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old part ofbuilding base

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best practice forconverted roof,


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Figure 8.8 Simulation results heating energy demand - Mid-terrace house

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Figure 8.9 Simulation results heating energy demand - Detached bungalow

As can be seen from the results, the combination of additional space and retrofit of the existing building leads to a high energy saving potential.


8.5 Evaluation of installation procedure for roof systems A series of projects using the Corus prefabricated Hi-point roof system were studied. Hi-point is an advanced modular roofing system using lightweight cold-formed steel sections. The system is a cost-effective solution for both new-build and refurbishment projects. It has been used for various projects ranging from apartments, military accommodation, offices, health care centres and schools. Hi-point components are either transported to site as complete units preassembled under factory controlled conditions, or, where space allows, delivered as a kit of parts ready for assembly at the ground level and then lifted into position. Hi-point roofing consists of a primary and secondary frame. The primary frame is the module structure while the secondary frame includes the purlins and roof coverings.

The manufacture/construction sequence is illustrated in Figure 8.10.

Section cut to required lengths 2D roof frames

2D frame assembled into 3D frame Insulation applied to 3D module

Installation of roof covering on module Roof module loaded and transported to site

Figure 8.10 Manufacturing sequence for Hi-point roof

Figure 8.11 shows the installation sequence for the Hi Point roof at the Unity Building, Liverpool (UK). This 27 storey residential building is part of a mixed use development. The scale of the project, height (94 m above ground level) and the location of the building in the heart of city centre mean that speed of installation and increased safety by reducing working at height were important considerations. 22 modules were constructed in the factory, transported to site and craned into position in just 2 days. The roof system was equipped with 1.2 mm clad aluminium standing seam sheets.


Hi-point Modules craned onto roof Hi-point Modules bolted on the roof steel frame

Roof top view during module installation Completed building

Figure 8.11 Hi-point roof installed at Unity Building, Liverpool

8.6 Investigation of the application of innovative roofing systems in renovation

The options to integrate active energy ‘creation’ systems in a roof are partly similar to the solutions presented for the facades earlier in Section 5.10. Active energy creation systems for residential buildings includes roof tile PVs, roof integrated and roof mounted PV panels and PV-film laminate onto aluminium and/or steel substrates. Roof-mounted vertical and horizontal axis wind turbines are also on the market. A recent invention is a portable wind turbine for roof application. Due to the small dimension of the turbine, application on various building types should be possible and an array of these turbines can be installed on large flat roofs (see Figure 8.12).

Figure 8.12 Array of small scale vertical axes wind turbines on a flat roof (rendered image from www.innoenergie.de)

The following sub-sections very briefly describe innovative roofing systems, suitable for renovation applications, which collect solar energy and convert it into thermal or electrical energy to cover a part or all of the building’s energy demand for space heating, hot water heating and/or electricity generation.


8.6.1 Steel roof integrated solar PV system

The system consists of amorphous silicon PV panels directly laminated on a standing seam steel roof. The area of the PV laminate is 2.16 m2. The rated power and operating voltage are 64 W and 24 V correspondingly. The system performance was measured at VTT’s test houses. In the climate of Helsinki, the system produces approximately 70 kWh/panel-m2 of electrical energy. The energy saving potential is 5-15% for an energy efficient detached house.

8.6.2 Standalone solar air heating system

The principle of the standalone solar air system is shown in Figure 8.13. The standalone solar air heating system comprises a roof integrated air collector, roof integrated PV system, fan, and heating duct work. The area of the air channel is 0.038 m2/m. The system application is meant for supplementary heating of houses, warehouses and other industrial buildings and drying of various products.

1.

2.3.

4.

5.

6.

7.

8.

1. Perforated plate for pressure difference

2. Black sheet metal cladding 'Classic'

3. Corrugated sheet as air channel

4. Roof integrated PV panel

5. Connecting channel

6. Electrical installations

7. DC fan

8. Air inlet terminal

9. Collector air channels

10. support for roofing

2.10.

9.

Figure 8.13 Principle of a stand-alone solar air system

The system was tested at VTT’s test houses (Figure 8.14). The profiled steel structure serves as the air channel for the collector. For sanitary reasons, the space for air circulation is made of sheet steel products. The collector is a standing seam sheet steel clad with a black surface. The PV system is directly integrated into the cladding. The test house dimensions were 2.4 7 m. The prototype system used a PV laminate of 0.394 5.486 m. The rated power and operating voltage were 128 W and 24 V correspondingly. The PV array output power is directly used for a ventilation fan. The nominal output voltage and power gives a maximum air flow of 120 - 150 litre/s for the ventilator.

The usable time for summer house application is 2-5 months during spring and autumn. The result of the test revealed that the system can deliver 1000-1500 kWh of heat into a house.

VTT’s test roof. The roof slope is approximately 30o, facing south Corrugated steel as air channel system.

Figure 8.14 Test roof for stand-alone solar air heating system


8.6.3 Solar integrated ventilation heating system

The solar integrated ventilation heating system comprises a roof integrated air collector, mechanical ventilation system with heat recovery, double flap valve control system controlled by temperature measurements, and air duct heaters at air inlet terminals (as shown in Figure 8.15). The system application is intended for primary heating system for detached and terraced houses. The structure and dimensions of the collector corresponds to the standalone system described above. The duct heating equipment can use any energy source: direct electricity, district heat, ground heat, pellet boilers etc.

1.

2.3.

4.

6.

7.

5.

1. Perforated plate for pressure difference

2. Black sheet metal cladding 'Classic'

3. Corrugated sheet as air channel

4. Connecting channel

5. Double flap valve control

6. Ventilation machine with rotating wheel heat exchanger

7. Air inlet terminals with heating elements

8. Exhaust air ducts

9. Summer fresh air 5.

1. Outdoor air 2. Indoor air3. Pre-heated air4. Air to heat exchanger

5. Air after heat exchanger

1.

2.

3.

4.5.

Temperature control points:

9.

8.

Figure 8.15 Principles of the solar integrated ventilation heating system.

The integrated solar air system can contribute 2000-2500 kWh to reduce a detached house’s heating energy demand. The energy saving potential depends on indoor temperature and ventilation rate. Especially during spring, all the heat collected from the roof cannot be utilised due to over-heating of the indoor air. The performance would improve if heat storage could be used as a part of the solar air system.

8.6.4 Roof integrated solar water heat collector

Laboratory tests using a hot box were carried out on a prototype roof-integrated solar water heat collector system. The principle of the system is that solar energy heats up water which circulates in tubes embedded in the external surface of the thermal insulation (Figure 8.16). Figure 8.17 shows the solar collector under construction.

Storage

PV or grid driven circulation pump with flow meter

Black sheet steel surface

Thermal insulation

Temperature measurement

ControlsAir flow measurement

Figure 8.16 Principle of roof integrated solar water heat collector


Figure 8.17 The liquid circulation tubes in the external surface of the thermal insulation

The solar collector was mounted in a vertical wall and irradiated by a solar simulator lamp producing an average intensity of about 640 - 690 W/m2. The efficiency and dynamics of the solar collector were measured for a range of temperature differences between the circulating water and the external environment. The main parameters measured were mass flow rate, temperatures in water inlet and outlet, temperatures through the roof construction and solar radiation at the external side of the sample. Throughout the tests, the principles of standard EN 12975-2 [27] were applied as far as possible. Based on these measurements, the thermal efficiency of the solar collector was calculated by dividing the energy transmitted to the circulating water by the solar radiation incident on the external surface of the collector.

Efficiencies of 20 – 55% were measured at mass flow rates of 0.005 – 0.012 kg/s at outdoor temperatures 0 - 10ºC. The results depend on the specific combination of conditions, for example a lower water inlet temperature or a higher mass flow rate or higher outdoor air temperature all lead to greater efficiency. Figure 8.18 shows the variation of efficiency with the temperature difference (Tm - Tcold), where Tm is the average collector water temperature and Tcold the outdoor air temperature.

0

0,1

0,2

0,3

0,4

0,5

0,6

0 5 10 15 20 25

Tm-Tcold

Eff

icie

nc

y (0

...1)

n (qm=0,005...0,012 kg/s)

Figure 8.18 Thermal efficiency of the solar water collector as function of Tm-Tcold


8.6.5 Study of a photovoltaic system on a roof-top extension

A parametric study of the energy generated by integrating photovoltaic (PV) cells into the roof of a roof-top extension was carried out which considered the feasibility of different schemes, the associated costs, the structural impact and the benefits. Five scenarios were studied which included two types of silicone crystalline panels at different orientations. The study showed that a significant amount of useful electrical energy could be generated due to the large areas on a roof which could be covered by a PV array. Typical payback periods for the scenarios studied were 15 years. (The systems come with a warranty of 25 years at 80% of their power, and have a design life of 50 years.)

8.7 Design guidance on roof-top extensions

8.7.1 Flat roof conversion

Two typical refurbishment options are; ‘Flat-to-pitched’ conversion or Flat to ‘Room-in-the roof’. There are lightweight cold-formed steel systems on the market and there are major opportunities for prefabricated lightweight steel solutions for this application. Some examples are shown in Figure 8.19.

Flat to pitch conversion using lightweight steel

Prefabricated lightweight steel system

Flat to room in the roof conversion using lightweight steel

Figure 8.19 Steel systems used in over-roofing of flat roofs

8.7.2 Pitched roofs conversion

Availability of headroom is a major consideration when converting loft space into habiatable space. The majority of the existing roofs can provide the minimum of 2.3 m headroom height required to be suitable for conversion. Dormer windows are widely used to increase the width of the room and available headroom.

The generic structural alterations to these roof types to create ‘room-in-the-roof’ space includes installation of:

New beams spanning from gable to gable/party wall to carry new floor load,

New floor joists between the existing joists,

Stud wall on top of the beam to support part of the roof,

New beams at the ridge level (or near the apex) spanning from gable to gable/party wall for long span rafters or large new dormer window (≥ 1.2 m) added,

Collars depending on the span of the rafters,

Removal of existing strutted, purlin or trussed internal members.

Traditionally, hot rolled steel beams are the preferred option despite the difficulty in installing the beams in available tight roof spaces. Sometimes the beam has to be cut into 2 or 3 small beams, which are then bolted together. This makes the logistics of loft conversion very tedious. The use of lightweight cold-formed steel for this application may be a better option.


8.7.3 Lightweight steel roof: “Open roof”

A light steel open roof system based on the use of cold formed C or Z sections was described in Section 8.3 and is illustrated in Figure 8.4. The members are easy to assemble on site using 12 or 16 mm diameter bolts located in pre-punched holes (although screws would also be possible). The roof system can be easily varied to suit the required living space and window openings such as Velux type roof lights. The roof may be a “warm construction” where insulations are applied externally by closed cell insulation board to which counter-battens and battens are attached. Slotted or perforated C sections for the rafters may be advantageous for “cold roof construction”, where mineral wool insulation is placed between the rafters.

Light steel open roofs based on ‘retro-fitting’ of timber trusses may be of two basic forms:

‘A frames’ consisting of rafters and bottom chords to the existing trusses, strengthened using C sections. In this case, the roof trusses span between front and rear façades.

Longitudinal lattice girders that support the existing timber rafters. In this case, new longitudinal trusses span between cross-walls or gable walls.

The practical use of open roof system is illustrated in Figure 8.20(a). The existing timber members are strengthened in one direction by C sections (element 1) that are screwed to the timber floor joists , and in the other direction by longitudinal roof trusses (element 3) that are attached to the existing masonry end walls. In order to allow for geometrical inaccuracies, C sections (element 6) are fixed to the walls and then the trusses are fitted between them and screwed to them.

a) Use of steel components in open roof system b) Typical room in the roof conversion with dormer

window

Figure 8.20 Illustration of space requirements in roof conversions

8.7.4 Dimensional planning for room in the roof space

For loft conversions, the minimum headroom (H) is between 2.3 to 2.4 m. Typically, dormer windows are used for shallow pitched roofs to increase the width of the usable space as shown in Figure 8.20 (b). Possible available headroom and room depth for a given roof pitch and span of existing roofs are presented below.

H = 2.3 – 2.4m

D = varies (see Table 4)


Available headroom for roof conversion Available room depth for loft conversion

Available Headroom (Ah) m 5 6 7 8 9 10 11 12

30o 1.44 1.73 2.02 2.31 2.60 2.89 3.18 3.46

35o 1.75 2.10 2.45 2.80 3.15 3.50 3.85 4.20

40o 2.10 2.52 2.94 3.36 3.78 4.20 4.62 5.03

45o 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00

*Note

Spans are measured between the wall plates.

Available Height (Ah) is the maximum ceiling heights available beneath the ridge (apex of the roof)

Approximately 400mm needs to be allowed for floor joists, ridge beam and finishings.

No allowance has been made for raised collar ties

Span Pitch

Not suitable as available headroom is limited

Possible But headroom ≤ 2.3 m after deduction of 400mm for floor joists, ridge beam and finishing

Suitable as headroom ≥ 2.3 m

Available Room depth (d) m 5 6 7 8 9 10 11 12

30o 1.88 2.88 3.36 4.36 4.84 5.84 6.32 7.32

35o 2.43 3.43 4.0 5.00 5.57 6.57 7.14 8.14

40o 2.85 3.85 4.50 5.50 6.14 7.14 7.78 8.78

45o 3.20 4.20 4.90 5.90 6.60 7.60 8.30 9.30

SpanPitch

Not suitable as available headroom is limited

Possible But headroom ≤ 2.3 m after deduction of 400mm for floor joists, ridge beam and finishing

Suitable as headroom ≥ 2.3 m

Existing timber joists are relatively small section of 50 x 75 to100 mm deep at 400 to 600 mm centres. These are too weak to carry the floor loads arising from loft conversion. As a result, these are normally left in place to support the ceiling. New light steel sections are installed between the existing joists to strengthen the existing joists. Existing timber rafter sizes are typically 50 x 75 to 125 mm deep. These rafters should be strengthened by either pairs of C sections joists either side of the timber sections, or installation of a steel beam to reduce the span of the timber sections.

An important requirement in roof conversion is to transfer the heavier loads from the habitable roof space to the existing foundations via the existing external walls. This is achieved by supporting new beam (or joists) supported on the external walls or party walls. However, where the existing internal walls are load bearing, the new beams or joists may be supported on these walls. In most cases, the existing foundations can support the additional loading but if not, underpinning of existing foundations is required. The general rule is that the additional load applied to the foundations should not exceed 20% of the original load. In the majority of housing, the internal load bearing walls stop at the first floor and the existing roof structure spans between the outer walls. Should there be a need to use the existing internal wall as load bearing, care must be taken to ensure that the existing foundation under this wall is adequate to carry additional load.

Beams are normally sized to be 200 mm longer than the actual span to provide 100 mm bearing each side on the support wall. Steel plates or concrete pad-stones are generally required under the support beams to spread the load onto the existing brick walls. For example, brick walls built with lime mortar have a low comprehensive strength of about 0.21 N/mm2 and so a 100mm x 200mm bearing can only support a load of about 4 kN at the beam position.

8.7.5 Roof insulation and condensation The up-grading of roofs has various effects on the thermal and energetic behaviour of a building. The following aspects have to be considered:

U-Value of the roof construction after renovation (including the effect thermal bridges). Modern buildings require a U value of less than 0.2W/m2K for roofs and often as low as 0.15W/m2K.

Creation of the additional floor space should add only a small amount to the building envelope

Control of over-heating (large surfaces are exposed to solar irradiation and are combined with little building mass)

Air permeability (need to improve the air-tightness of the new roof structure)

‘Warm roof’ construction is the most effective method of preventing condensation, but is only applicable to a new roof, an existing flat roof conversion by over-roofing, or where the existing roof tiles are removed and re-roofed. However, the latter may require planning permission because of alteration to the existing roof line.

Most loft conversions are ‘cold roof’, which involves upgrading the original roof from the inside. Typical practice involves adding insulation between and/or under the roof rafters. Measures to avoid


condensation risk are necessary because the existing felt layer is a non-breathable membrane. Condensation risk is avoided by either:

provision of cross ventilation above the insulation layer on the cold side of the roof, as shown in Figure 8.21(a).

or alternatively, the roof tiles could be removed and the existing traditional non-breathable felt layer is replaced with a vapour permeable layer (breather felt), as shown in Figure 8.21 (b). The ventilation gap above the vapour permeable layer can be reduced to 25mm.

Ventilation gap over insulation: 50mm gap for traditional non-breathable felt (25mm gap for modern breathable felt) Loft room

Ridge vents: 5mm gap

Eaves vents: 25mm gap

a) Cross ventilation of room-in-roof to avoid condensation risk

b) Between and under rafter insulation with modern breathable membrane

Figure 8.21 Ventilation strategies in over-roofing

8.7.6 Fire safety Provision of means of escape and fire protection is required for a roof-top conversion. Common practices to achieve compliance with fire safety regulations are:

The staircase must discharge close to a door leading to an external safe place and not to another room.

All doors openings and walls enclosing staircases must have at least 30 minutes fire resistance, with the exception of toilets and bathrooms doors.

Mains powered interlinked smoke detectors are to be provided, with a minimum of one detector per level.

The first floor ceiling should achieve at least 30 minutes fire resistance.

Dormer windows within 1 metre of a boundary are to have at least 30 minutes fire resistance in both directions. The dormer roof is to have at least 30 minutes fire resistance.


9 WP5: ECONOMIC AND SUSTAINABILITY JUSTIFICATION TOOLS & CASE STUDIES


9.1 Objectives The purpose of this Work Package is to develop simple software spreadsheet tools to be used at the pre-design stage for assessing the economic viability and environmental sustainability of alternative steel intensive renovation solutions. In addition, a series of case studies demonstrating the technologies studied in the preceding Work Packages have been prepared.

9.2 Economic justification software tool

9.2.1 Functional specification of tool

A multi-criteria tool was developed to support developers’ decisions regarding whether to demolish or renovate a building. The tool estimates the potential cost savings arising from over-cladding and/or over-roofing and/or constructing a roof-top extension using steel technologies. It includes issues such as savings in heating bills, reduced maintenance costs, improved visual aspects, increased rental value and the benefit of a longer building life. National variations in certain parameters are taken into account. It covers rectangular, multi-storey residential and commercial buildings and single storey industrial buildings.

The main result provided by the tool is the payback period. To calculate it, the most difficult issue is the determination of the energy savings following renovation. The tool gives two methods for the calculation of the energy savings:

A simplified method whereby the energy savings are estimated by the tool itself based on empirical relationships

A direct input method whereby the user can input the results from a more detailed energy calculation using a third party thermal simulation software.

The economic model takes into account the net present value of the following parameters (where relevant) for the calculation of the payback period:

Cost savings arising from energy savings after renovation: The energy demands of the building before and after renovation are be estimated using one of the two methods described above. In order to convert the energy savings into cost savings, energy costs for different sources of energy are user inputs as these vary from one country to another.

Savings due to reduced maintenance: Maintenance costs due to repair of the existing facades and roofs are expected to increase over time in the absence of over-cladding. Over-cladding therefore leads to a decrease of the maintenance costs due to arrested deterioration.

Increased rental income following renovation: Rental charges are expected to be increased following renovation due to the higher quality environment. In order to estimate the increased rental income, rental charges for commercial, residential and industrial buildings are user inputs as these vary from one country to another.

Additional income due to additional space: Over-cladding work is often combined with the creation of new floor level(s) by a roof-top extension. This creates additional rental income with the rental charges for these new built spaces being generally higher than those of the original parts of the building. For estimating the income generated by the rent of such additional spaces, rental charges for roof-top extensions are user inputs as these vary from one country to another.


Construction costs: Construction costs for over-cladding, over-roofing and roof-top extensions, and for residential, commercial and industrial buildings are user inputs as these vary from one country to another.

Cost of borrowing to pay for the renovation work: The amount of interest paid when financing the renovation work with a loan is taken into account in the calculation.

9.2.2 Parametric studies

Parametric studies using full building thermal simulation software tools have been carried out in order to derive empirical relationships between the key parameters affecting the energy performance of buildings. Figure 9.1 shows the four storey office building, ten storey residential and single storey industrial building models. The effect of the following parameters on energy performance was identified:

Building location (climate)

Building dimensions (shape and height)

Building orientation

Percentage glazing (rooflights for the industrial building)

U-values (U-values of façade and roof varied separately)

Air-tightness

Addition of a roof-top extension (residential and commercial building only)

Figure 9.1 Office (left), residential (middle) and industrial (right) reference buildings for parametric studies

The energy demand of a building is a multidimensional function of its components (described by parameters xi), the climate and the building use. The energy demand Qp,orig of a building before renovation (original state) can be expressed as follows:

)use,climate,,....,( orign,orig1,origp, xxfQ

Similarly, the energy demand Qp,retro of the same building after renovation (retrofitted state) can be expressed as follows:

)use,climate,,....,( retron,retro1,retrop, xxfQ


The parametric studies provided numerous useful results showing the effect of the considered parameters on the energy performance of the buildings. Figure 9.2 shows the annual heating load for several configurations of a residential building including the reference building (labelled 1960) as well as the building in various renovated states (entirely over-clad (2008), with over-cladding on the façade only, with over-cladding on the façade and a pitched roof and with over-cladding on the façade with a roof-top extension). This graph shows that significant energy savings can be made using renovation.

Figure 9.2 Annual heating loads for various configurations of a residential building

Figure 9.3 shows the annual heating and cooling loads for several configurations of a commercial building including the reference building (labelled 1960) as well as the building in various renovated states (entirely over-clad (2008), with over-cladding on the façade only, with over-cladding on the façade and a pitched roof and with over-cladding on the façade with a roof-top extension). This graph shows that whereas significant energy savings are possible by renovation, the cooling energy demand of a building compliant with current energy performance standards (typically built in 2008) is actually higher than that of an old building (typically built in 1960). Although, the original scope of the tool was limited to the estimation of the heating energy demands, the above results showed that it was not possible to ignore the effect of renovation on the cooling energy demand of commercial buildings, as it increases with the performance of the thermal envelope which would lead to an unacceptable overestimation of the energy savings. Additional simulations were therefore carried out for commercial office buildings to provide more data on the effect of renovation on the cooling energy demands with a view to derive empirical relationships which make allowance for the cooling demand.

For both residential and commercial buildings, the empirical relationships between the key parameters affecting the building energy performance and the energy demands were incorporated into a simple calculation method applicable to all buildings. The detailed report of the parametric study for office buildings is available in a WP1 activity report from RWTH and for the residential building is available in a WP5 activity report from Oxford Brookes University (sub-contractor to SCI). The detailed report of the parametric study for industrial buildings is available in a WP2 activity report from Corus.


Figure 9.3 Annual heating and cooling loads for commercial buildings

9.2.3 Derivation of empirical relationships building energy demands

As described in the section 9.2.2, the energy demand of a building is a multidimensional function of its components. In order to define such function f, it was originally proposed to assess the sensitivity or effectiveness of the various parameters xi (as listed section 9.2.2) using partial derivatives:

)()(essEffectiven retrop,xi Qxi

This method however lead to very large differences between the estimated energy demands and those calculated via full thermal analysis and was therefore considered inadequate.

As a second attempt, the heat loss calculation as shown in equation (9.1) below was used for the estimation of the heating energy demands (which corresponds to the total energy demands in the case of the residential and industrial buildings):

)36001000

()(

)(31,00.12

1,00:01

airair

ii

pBuildingwindowwindowroofroofwallwallDecstpmi

Janstamiextref

CVACHAUAUAUTT

kWhDemandHeating

(9.1)

where:

T denotes a temperature (K)

U denotes a U-value (Wm-2K-1)

A denotes an area (m2)

ACH denotes the air change per hour (hr-1)

V denotes a volume (m3)

Cp air denotes the specific heat of air (kJkg-1K-1)

air denotes the density of air (kgm-3)

As compared to the results from the full thermal analyses, the above heat loss calculation led to significant differences in terms of the calculation of the energy demands and savings (+/- 20%) and this solution was therefore discarded. However, the basic format of the heat loss calculation was retained for the definition of the empirical relationships as it identifies the contribution of the following elements to the total heating energy demand:


Climate, via the difference between internal and external temperatures

Heat loss through walls

Heat loss through the roof

Heat loss through the windows / roof-lights

Heat loss via air-infiltration

The heat loss calculation was therefore modified into the following generic expression for the calculation of the heating energy demands:

)()()()(

)(

4321 Buildingwindowwindowroofroofwallwallk VACHfAUfAUfAUfT

kWhDemandHeating

(9.2)

cbxaxxfformtheoffunctionsquadraticareffff

TTTwhereDecstpmi

Janstamiextirefk i

24321

31,00.12

1,00:01

)(,,,

)(

The above generic expression is valid for the empirical relationships defined for all the three building types, however Tk, f1, f2, f3 and f4 are different for commercial, residential and industrial buildings.

In equation (9.2), the term Tk is the sum of the hourly difference between the internal temperature and a reference temperature. The hourly external temperature Text was defined according to meteorological data and the reference temperature Tref is equal to the inside temperature minus a constant (the inside temperature was defined according to the heating profile used in the relevant full thermal analyses). This constant was chosen so that the difference between the heating demand as calculated according to expression (9.2) and that obtained from the full thermal simulations was minimal (via the computing of f1, f2, f3 and f4 ). The subscript k of Tk differentiates T for the various climates considered as it will not have the same values for the London, Berlin and Helsinki climates, due to the different external temperatures. However, the constant used to calculate Tref from the internal temperature is the same, irrespective of the climate considered.

The variables of the quadratic functions f1, f2, f3 and f4 namely UwallAwall, Uroof Aroof, UwindowAwindow and ACHVbuilding have been normalised so as to be able to describe any building size or shape (by considering areas and volumes). These variables respectively characterise the heat loss through the walls, roof and windows as well as the heat loss via air-infiltration.

The difference between the heating energy demand as calculated via the empirical relationships defined according to equation (9.2) and the heating energy demand as calculated via the full thermal analyses carried out for residential and industrial buildings are considered to be within an acceptable range (+/- 9%) for the purpose of the economic justification software tool.

The empirical relationship for the calculation of the cooling energy demand for commercial buildings was derived using the same generic expression as that described above for the estimation of the heating energy demands. The difference between the cooling energy demands as calculated via the empirical relationship and that calculated via the full thermal analyses are also considered to be within an acceptable range (+/- 10%).

9.2.4 Implementation of software tool

The software tool was implemented into a spreadsheet using Microsoft Excel. The following figures show screenshots of the tool.


Figure 9.4 Screenshot of software tool homepage

Figure 9.5 Screenshot of ‘Renovated building’ section of software tool


Figure 9.6 Screenshot of ‘Results’ section of software tool

9.2.5 Conclusions

In terms of energy savings, the economic justification tool indicates that combining over-cladding and over-roofing leads to the highest reduction in energy demands. In terms of payback period, the tool indicates that the over-roofing solution used on its own has the shortest payback period due to its relatively inexpensive nature and the substantial energy savings generated. The tool also shows that renovation solutions using over-cladding (without a roof-top extension) lead to the longest payback periods due to relatively high construction costs compared to the energy savings achieved. Finally, the tool indicates that renovation solutions with roof-top extensions lead to the highest returns on investment over time due to the combination of additional income from additional rental space and improved energy efficiency.


9.3 Sustainability justification software tool A simple spreadsheet tool was developed which estimated the embodied carbon of a range of renovation solutions for industrial, commercial and residential buildings.

9.3.1 Derivation of relationship between U-value and embodied carbon

A matrix of thirty-six different renovation solutions for industrial, commercial and residential buildings was developed, based on current practice in Europe. The solutions covered:

Over painting

Over cladding of walls

Over roofing

Strip and re-cladding of walls

Strip and re-roofing

Roof top extension/creation of habitable roof

Figure 9.7 shows six examples of the renovation systems reviewed.

Build up system showing over roofing and wall over cladding of asbestos sheet

Over roofing of asbestos sheet and over cladding of brick using Corus Composite PUR panel

Brick slips with closed cell insulation, backing sheet and sub-frame

Flat to pitched roof truss system with steel liner

Tile system on Composite panels with Rockwool

Figure 9.7 Examples of typical renovation options reviewed

Ten of the solutions were selected for Life Cycle Assessment (LCA) in order to develop an algorithm for describing the empirical relationship between the U-value of each renovation option and associated embodied carbon emission CO2/m2. Material bills of quantities for the ten selected renovation options were first collated. The data consisted of weight, volume, area and thickness of construction layers of each renovation options. For each solution, a carbon footprint analysis was undertaken using existing LCA data from Confidex Sustain Environmental Product Declarations (EPD) [28] or using embodied CO2 data from publicly available data such as GaBi Professional LCI Database [29] and Bath ICE [30]. The analysis covered a wide range of U-values (0.15 – 0.45 W/(m2K)) for each refurbishment solution. Adjustments were made to account for increase insulation thickness and steel bracket for these ranges of U-values.


The following assumptions were made for the carbon footprint analysis, partly based on the assumptions used in generating the original cladding EPDs:

Life Cycle Assessment data is “Cradle to Grave” Purlins and rails are included where required

Substitution/system expansion methodology use Composite panel insulations types are PUR/PIR

Plastisol coating on top sheet and polyester on bottom sheet

Blowing agent in PUR/PIR insulation is pentane

100% recycling of the steel at end-of-life in the case of composite panel

Build up systems insulation are based on mineral wool insulation

79% recycling + 15% reuse in the case of built-up systems

Steel content of Build up systems is the same as Cassette tray systems

Miscellaneous components e.g., profile fillers, mastics, VCL membrane and others not included

Inner steel panel is taken as 0.4mm thick

External steel built up panel is taken as 0.7mm thick

Insulation is land-filled at end-of-life

Composite panel (foam) – both internal and external steel are taken as 0.5 mm thick

Figure 9.8 presents the renovation options analysed. The outcome of the carbon footprint analysis is shown in Figure 9.9. The graph shows the embodied carbon emission (KgCO2/m

2) with corresponding thermal transmittance (U-values W/m2K) for each of the ten selected renovation options. From these data sets, empirical relationship between embodied carbon emissions and U-values was developed using sixth order polynomial equation for each of the renovation options. An example of the equation is shown on the graph. The graph shows that the embodied carbon emissions of the composite panels (A2, B2, C2 and E2) are higher than the built up systems (A1, B1, C1 and E1). This is because the carbon content of PUR/PIR foam insulation is higher than mineral wool insulation.

Figure 9.8 Ten renovation solutions implemented into the tool


y = 0.0015x6 - 0.0393x5 + 0.4185x4 - 2.227x3 + 6.2611x2 - 9.6547x + 31.013

R2 = 1

0.0

10.0

20.0

30.0

40.0

50.0

60.0

0.15 0.2 0.25 0.3 0.35 0.4 0.45

U-Value (W/m2.K)

Em

bo

die

d C

arb

on

(K

gC

O2/

m2 )

A1

A2

B1

B2

C1

C2

D1

D2

E1

E2

Poly. (D1)

Figure 9.9 Embodied carbon versus thermal transmittance for renovation options

The graph also shows that as the thermal performance of the envelope improves, the embodied carbon emission increases. This is largely due to the increase in insulation thickness to achieve the lower U-values. This highlights the fact that, as the building becomes more energy efficient and operational energy decreases, the embodied energy considerably increases as a proportion of the whole lifecycle emissions of the building. Earlier studies have shown that the total embodied energy for low energy buildings significantly increases as the operational energy reduces, and studies on low energy housing showed that embodied energy can account for as much as 40 – 60% of total energy use [31,32,33]. Nonetheless, the overall carbon emission of low energy buildings or buildings refurbished to current thermal regulatory requirement is much lower than those of buildings built before the 2006 thermal regulations.

These findings underline the importance of holistic assessment of both operational and embodied carbon contents of buildings. The current practice of single consideration of operational energy during the design phase is potentially misleading and incomplete.

9.3.2 Development of tool

The tool is a Microsoft Excel spreadsheet with three simple worksheets. The first worksheet provides an introduction to the tool, a step-by-step user guide and lists the assumptions. The second worksheet is the input interface (Figure 9.10). Radio buttons at the top of the page enable users to filter the building types (industrial, commercial and residential), renovation options, etc. The tool facilitates various combinations of analysis. The ‘add solution’ button enables users to add each combination of analysis to the existing solutions table. This table is linked to the report interface, where the results of single and/or combinations of the analysis are plotted on a graph as shown in Figures 10 and 12.


Figure 9.10 Input interface

9.3.3 Demonstration of tool for Potters Place case study

The tool was used to compare four renovation solutions for Potters Place, a typical large-size 1960s industrial shed which underwent a total refurbishment (see Section 6.6.1):

Over cladding of wall using Built-up system (Solution 1) vs Composite panel (Solution 2).

Re-cladding of wall using Built-up system (Solution 3) vs Composite panel (Solution 4).

The outcome of the analysis is presented in Figure 9.11. Solution 1 (over-cladding using a built-up system) provides the lowest carbon emission due to the relatively lower material content of the systems. Over-cladding the existing façade with a built up system only required attaching steel brackets to the existing façade and outer steel skin with a mineral wool sandwich between the existing wall and the steel outer skin. On the other hand, a composite panel system consists of a steel bracket attached to the existing wall and two steel skins and PUR/PIR (rigid polyurethane and polyisocyanurate). This system has more material and carbon content.

From the result, it is also worth noting the slightly lower carbon content of Solution 4 (recladding using composite panel) compared to Solution 3 (over-cladding using composite panel). The reasons for this is that over-cladding using composite panels generally requires new sets of brackets and purlins to attach the composite panel to the existing façade, whereas recladding involves stripping the existing façade to the existing steel purlin to receive the composite panel. Therefore, the tool assumes that the majority of the existing purlins could be reused for recladding option. Also, the tool does not take into account the carbon impact associated with the removal and disposal of the old existing façade. This is extremely difficult to assess and outside the scope of this project.


Figure 9.11 Graph showing renovation solutions comparison

9.4 Assessment of renovation in BREEAM and HQE A study was carried out of the rating that a vertical extension can achieve using two environmental assessment rating tools. (The rating was just applicable to the extension and not to the whole development). The two assessment methods considered were the BREEAM (Building Research Establishment Environmental Assessment Method) Bespoke assessment undertaken at the Design and Procurement (D&P) stage and the HQE (High Quality Environmental standard) method, the standard for green building in France.

Both environmental assessment methods are voluntary schemes that aim to quantify and reduce the environmental burdens of buildings by rewarding those designs that take positive steps to minimize their environmental impacts. Despite the fact that one system is English and the other French, they both deal with the harmonious relationship between buildings and their immediate environment with similar key themes. On this basis, in the case of an actual vertical extension project, a formal assessment would be undertaken with the Bespoke checklist defined by BRE based on an accurate brief of the project at the design stage. However, in order to carry out this exercise, a simulation of a Bespoke scheme was set up listing all the potential credits applicable to specifically assess this kind of project.

By using the HQE checklist, or creating a checklist as BRE would have done, it was possible to determine which credits were easily achievable, which credits were hard to achieve due to the nature of the project and which were not even applicable.

Credits were categorised into four groups:

Credits which are recommended for this kind of development as they are achievable to all projects irrespective of size or location.

Credits which are site specific and cannot be assumed on all projects, however they can be pursued/achieved where appropriate

Credits which are the most difficult to achieve in terms of procedure, design or may exceed cost targets, they require a particular design enhancement which could however be necessary to achieve the targeted rating.

Credits which were not be applicable in the case of a "vertical extension"


Table 9.1 summarises the allocation of credits across all 10 BREEAM sections.

Table 9.1 Summary of BREEAM assessment

BREEAM SCORING MATRIX

BREEAM ENVIRONMENTAL

WEIGHTING

Recommended credits

A

Site specific credits

B

Enhanced design credits

C

Non applicable

DTOTAL

CREDITS

MANAGEMENT 12% 12 1 7 1 20

HEALTH & WELLBEING 15% 13 0 2 1 16

ENERGY 19% 11 0 13 0 24

TRANSPORT 8% 1 5 0 6 7

WATER 6% 5 0 2 1 8

MATERIALS 13% 13 1 4 1 18

WASTE 8% 4 0 2 0 6

LAND USE & ECOLOGY 10% 5 9 2 5 12

POLLUTION 10% 3 6 4 6 13

INNOVATION 1 0 8 0 9

A+C+D

TOTAL CREDITS 68 22 44 21 133

The study showed that a significant number of credits are site specific and hence not directly applicable to a vertical extension. If the whole building is assessed (existing building + vertical extension), then the final rating will almost entirely depend on the existing building.


9.5 Case studies illustrating the technologies studied in this project

Eleven case studies were prepared which illustrated recent applications of the technologies studied in this project in different European countries. A summary of four of the case studies is given here:

Over-cladding of industrial shed using SolarWall™ system (Durham, UK)

The south eastern elevation of an existing industrial building was over-clad with 410 m2 of metal SolarWall™ system and the heating energy contribution was monitored over 12 months (see also Section 5.10.2). The heat collected and delivered to the building ventilation system amounts to 19% of the total heating energy requirement, i.e. 70,061 kWh out of 365,974 kWh. The SolarWall™ together with the ventilation system which reduced air stratification in the building, led to a reduction in gas-fired heating requirement of 303,543 kWh. This equates to 58.9 tonnes of CO2 or 51% of previous year consumption prior to SolarWall™ installation.

Metal SolarWall™: Perforated cladding SE Elevation over-clad with SolarWall™

Figure 9.12 SolarWall™ cladding on industrial building in Durham, UK

Over-cladding of industrial building using composite panels (Scotland)

About 11,500 m2 composite panels achieving 0.25 W/m2K was installed on this industrial building. The project was completed within 30 weeks without disruption to production. The key feature of this project was the installation of new cleats to the steel rafter and roll-formed purlins attached to receive the new cladding. The reason for this was the fact that the existing purlin spacings were inadequate to support the new composite panels.

Hole cut through the roof and new cleat connected to the rafter

Installation of new composite panel on new purlin

Figure 9.13 Installation of composite panels on industrial building in Scotland


Roof-top extension of university building in Rzeszow, Poland

A 1950s, in-situ concrete, three storey building was renovated by adding two new storeys. As construction work was only possible during three months summer holidays, light steel framing was chosen for the roof-top extension, so that the new structure was easy and fast to assemble, with minimum intervention to the old building. The external walls were made of light steel sections (C 90 or C 140 C-shaped profiles), at 600 mm spacing, placed at their top and bottom in U 90 or U 140 U-shaped profiles.

The thermal performance of the façade was well below modern requirements, so it was renovated by installing new windows and applying an ETICS (External Thermal Insulating Composite System) layer to the existing façade to increase the insulation level considerably.

Roof-top extension during construction Renovated building showing its 2 new floors

Figure 9.14 Roof-top extension of university building in Rzeszow, Poland

Renovation of office building in Milan

The 1960s Valtellina office complex underwent a substantial renovation in two successive construction operations in 2006. The structure of the former building was untouched and retained as the load-bearing skeleton whilst the facades, roof and indoor spaces were refurbished.

Photo of building before renovation Completed building

Figure 9.15 Valtellina office building in Milan

A 600 m² steel and glass double skin was added to the main façade, enabling energy savings as well as architectonical lightness. The outer and inner skins were separated by 60 cm. This space acts as a buffer zone to reduce the need for additional heating or cooling. Dependent on the conditions, warm or cold air is drawn from the offices or from the outside and rejected through glass louvres located on the upper side of the external skin. Both the flows and openings of the louvres are controlled by a central computer connected to sensors placed inside the space between the two glass skins.


10 CONCLUSIONS

This project studied the renovation and improvement of existing residential, industrial and commercial buildings using steel-based technologies, focusing on techniques such as over-cladding, over-roofing and roof-top extensions.

The air-tightness and thermal performance of buildings in Poland, Germany and UK were measured before and after renovation. It was clear that current practice of over-cladding and over-roofing existing buildings does not seem to reliably improve the air-tightness of buildings and it is recommended that an air barrier is introduced on the inside of the building to reduce heat losses due to cold air infiltration. This also reduces the risk of condensation in the cavity behind the over-cladding system. Guidance on practical strategies for achieving this was developed.

Thermal simulations of single storey industrial buildings and multi-storey residential and commercial buildings before and after renovation were performed in order to determine the potential energy savings arising from renovation. The simulations showed that very significant savings could be achieved: over-cladding can reduce the heat transmission losses through the over-clad façade by over 80% and similar savings are possible with over-roofing. However, improved thermal insulation of an office building resulted in increased cooling demand as well as decreased space heating demand. Therefore, renovation of an office building should include some passive cooling measures, for example, exterior shading which can help to reduce the cooling demand by around 50%. The scope of a renovation project (i.e. which building elements to upgrade) and targeted level of improvement in thermal performance largely depends on the reasons for renovating the particular building, such as national regulatory requirements, acceptable level of return on investment in different countries etc.

Field trials were carried out on over-cladding systems using large steel flat panels incorporating a novel Transpired Solar Collector (TSC) system. In general, the measured data supported the energy balance predictions and prove that flat panel TSCs are a competitive over-cladding solution for residential and commercial buildings. The usability of this heat depends on the occupancy pattern and climatic conditions, which should be investigated in continuing research. Field trials were also carried out on a prototype solar thermal storage wall system which demonstrated it is a good solution for south-facing elevations. Other innovative air and water-based heating systems that absorb solar energy were investigated in this research, and again, these could be developed further.

Laboratory tests were carried out to determine semi-rigid corner joint characteristics of bolted lap joints used in thin-walled steel portal frame structures suitable for roof-top extensions. Recommendations were developed regarding how a vertical light steel framed extension can be connected to an existing concrete building and load tests were carried out to prove different systems.

The potential for light steel systems to provide new habitable space by renovating existing timber roofs was studied. Various forms of light steel roofing technologies were investigated, either using lightweight elements that can be man-handled into position in an existing roof space or using larger pre-fabricated components in which the whole roof is replaced. Thermal simulations demonstrated the energy savings that can be achieved by upgrading the roofs of existing houses. Additional energy generation can be achieved by roof-integrated air and water heaters and collectors and laboratory tests were carried out to measure the efficiency of a prototype roof-integrated solar water heat collector system.

The thermal simulation data were used to develop a simplified tool for assessing the economic viability of alternative steel intensive renovation solutions. A simplified tool for comparing the embodied carbon of different renovation systems was also developed. These tools enable different solutions to be easily compared.

A series of Case Studies was prepared to illustrate the practical use of these renovation technologies.


11 EXPLOITATION AND IMPACT OF THE RESEARCH RESULTS

11.1 Technical and economic potential The main economic potential for use of the results is in the over-cladding and over-roofing of existing buildings to improve their energy performance of remaining life. It is recognised that existing buildings are the main source of CO2 emissions in the EU, and housing and residential buildings represent approximately 27% of total CO2 emissions. Therefore, an improvement of residential buildings by additional steel-based insulated façades and roof-top extensions will have important social, economic and environmental benefits. The technologies developed in this project will have immediate impact and will lead to new market opportunities for the steel sector across Europe.

The use of steel in over-cladding systems is increasing, particularly where there are requirements for a high level of prefabrication. The extension of buildings by one or two floors in light steel framing or modular construction is already a niche market, and will increase.

The test work and long term monitoring provides much needed performance data, which will be exploited by the partners. The field trials on the use of a Transpired Solar Collector to over-clad a residential university building is the first known application of this kind and the data measured will be important in the ongoing development and optimisation of this very promising system.

The project partners have had discussions with manufacturers of steel renovation products, explaining the relevance of the findings of this project to the manufacturers’ particular product ranges. It is expected that these contacts will lead to further co-operation as the technological advances made in this project are disseminated. For example, the Polish company AmTech, a manufacturer of light steel framing systems and roof-top extensions, has expressed interest in the application of the project results in future renovation schemes.

11.2 Dissemination of results A project web site www.steel-renovation.org was created for disseminating the project deliverables. From this page, all the activity reports can be downloaded, as well as the final summary report. The project partners will promote the web site to the target audiences in their countries.

The coordinator, SCI, has been invited by the Institution of Civil Engineers in the UK to prepare a paper on Renovation of Buildings using Steel Technologies for a Special Issue of its Proceedings: Structures and Buildings. It is anticipated that other research papers describing the work carried out under ROBUST will be published in the coming year.


12 LIST OF FIGURES

Figure 3.1 Homepage of ROBUST project site 14

Figure 4.1 Examples of over-cladding of concrete panel buildings using horizontally orientated metallic panels 18

Figure 4.2 Two storey extension of an existing building using light steel framing, Rotterdam 19

Figure 4.3 Roof-top extension using modules at Plymouth University, UK 19

Figure 5.1 Representation of over-clad building using large steel cassette panels 24

Figure 5.2 Various forms of light steel sub frames in over-cladding systems 24

Figure 5.3 Relative impact of energy saving measures on a residential building's heating energy demand 27

Figure 5.4 Cross-section of the analysed facade system 29

Figure 5.5 Performance parameters 30

Figure 5.6 Reference wall (left) and the double-skin wall (right) 32

Figure 5.7 Office building used in simulations 33

Figure 5.8 Simplified roof-top extension office building 35

Figure 5.9 Cross-section and photos of the thermal storage wall during assembly 38

Figure 5.10 A schematic view of a transpired solar collector 41

Figure 5.11 Tower block at Oxford Brookes University used for over-cladding tests and a cross-section through the original concrete façade panel 42

Figure 5.12 Location of the perforated panels on the south facing wall 43

Figure 5.13 Completed over-clad façade on first two floors above podium level, Aug 2009 43

Figure 5.14 Test results for cool but sunny day (25 September 2010) 45

Figure 5.15 Test results for 10 February 2010 45

Figure 5.16 Simple energy balance on the perforated absorber 46

Figure 5.17 Instantaneous thermal efficiency against flow rate for 3 wind velocities (based on the assumptions in RETScreen® V3.1 and using an absorptivity of 0.9) 47

Figure 5.18 SolarWall® TSCs installed on the south wall of Beaconsfield service station (UK), where the TSC preheats the ventilation air for the food court 48

Figure 6.1 RWTH building – south elevation 53

Figure 6.2 IR image of RWTH building – south elevation 53

Figure 6.3 Laboratory hall before and after renovation, Aachen 54

Figure 6.4 Industrial building before and after renovation, UK 54

Figure 6.5 Existing cassette wall (a), IR image of cassette wall from hot box test (b) 55

Figure 6.6 Re-cladding with additional insulation layer (Rockwool: “Steelrock”, left), over-cladding using steel sandwich elements (right) 55

Figure 6.7 Hot box with IR camera (left), result for re-clad cassette wall (right) 56

Figure 6.8 Effect of additional insulation layer on the performance of steel cassette systems 56

Figure 6.9 Techniques for achieving air-tightness in renovation 59

Figure 6.10 Annual energy demand for 60 m x 120 m x 10 m single storey warehouse 61

Figure 6.11 Annual energy demand for 30 m x 60 m x 6 m high single storey warehouse 62

Figure 6.12 External view of Potters Place before renovation 63


Figure 6.13 Installation of fans for air-tightness test 63

Figure 6.14 Model of Potters Place after renovation 64

Figure 6.15 Milton Keynes case study, Units 2 – 4, before renovation 67

Figure 6.16 Milton Keynes case study, Unit 16, after renovation 67

Figure 6.17 IR image and photo of tested walls of the “L” buildings (before renovation) 69

Figure 6.18 IR image and photo of the “L” buildings (after renovation) 69

Figure 6.19 Production hall roof (Building B before renovation) 70

Figure 6.20 Production hall walls (Building B, after renovation) 70

Figure 6.21 Sports hall (left: before renovation, right: after renovation, not fully completed) 70

Figure 6.22 Air-tightness test, using three fans (left), result (right) 71

Figure 6.23 IR image after renovation (ambient temp.: -3 °C, indoor: 23 °C) 71

Figure 6.24 IR image after renovation (ambient temp.: -3 °C, indoor: 23 °C) 71

Figure 6.25 Concrete wall, refurbished with steel sandwich panels 72

Figure 6.26 Over-cladding using a cassette wall or sandwich panel (left and right respectively) 72

Figure 6.27 Over-roofing using composite panels (left) and built-up roofing system (right) 73

Figure 7.1 Vertical extensions in residential buildings 74

Figure 7.2 Vertical extension in industrial and office buildings 75

Figure 7.3 Case study of a vertical extension: typical scheme showing key interfaces 77

Figure 7.4 Several types of connection: column to concrete wall 78

Figure 7.5 (a) Pinned connection and (b) fixed connection 78

Figure 7.6 Concrete/steel connection: Frictional, end plate, anchors 79

Figure 7.7 Post-installed fasteners types 79

Figure 7.8 Point connection for continuous connection on a concrete walls 81

Figure 7.9 Anchorage of the lower U-track in the compression slab 81

Figure 7.10 Connection under study with laboratory set up: Left: test 1 and right: test 2 82

Figure 7.11 Numerical model of the connection 83

Figure 7.12 Moment-rotation curve for connection 84

Figure 7.13 View of failed elements (test 2) 84

Figure 7.14 The test arrangement 85

Figure 7.15 Arrangement for the test rig frame 86

Figure 7.16 Results for pinned portal frame test 86

Figure 7.17 Results for fixed portal frame test 87

Figure 7.18 Failure modes in concrete base 87

Figure 7.19 Wall build-up and wall panel prior to test 88

Figure 7.20 Test set-up 88

Figure 7.21 Load–horizontal displacement curves at the end posts 89

Figure 8.1 Examples of roofs 90

Figure 8.2 Common structural forms of timber roofs 91

Figure 8.3 Typical structural modifications to roofs to create habitable space 91

Figure 8.4 Forms of Open Roof Systems 93


Figure 8.5 Deflection shape of an 8 m span open roof truss under imposed and dead load applied to the floor 94

Figure 8.6 Monthly heating energy demand, semi detached house, base case (left: whole building, right: energy demand caused by heat transmission through roof) 96

Figure 8.7 Monthly heating energy demand of converted loft in a semi detached house (left: good practice, right: best practice) 96

Figure 8.8 Simulation results heating energy demand - Mid-terrace house 97

Figure 8.9 Simulation results heating energy demand - Detached bungalow 97

Figure 8.10 Manufacturing sequence for Hi-point roof 98

Figure 8.11 Hi-point roof installed at Unity Building, Liverpool 99

Figure 8.12 Array of small scale vertical axes wind turbines on a flat roof 99

Figure 8.13 Principle of a stand-alone solar air system 100

Figure 8.14 Test roof for stand-alone solar air heating system 100

Figure 8.15 Principles of the solar integrated ventilation heating system. 101

Figure 8.16 Principle of roof integrated solar water heat collector 101

Figure 8.17 The liquid circulation tubes in the external surface of the thermal insulation 102

Figure 8.18 Thermal efficiency of the solar water collector as function of Tm-Tcold 102

Figure 8.19 Steel systems used in over-roofing of flat roofs 103

Figure 8.20 Illustration of space requirements in roof conversions 104

Figure 8.21 Ventilation strategies in over-roofing 106

Figure 9.1 Office (left), residential (middle) and industrial (right) reference buildings for parametric studies 108

Figure 9.2 Annual heating loads for various configurations of a residential building 109

Figure 9.3 Annual heating and cooling loads for commercial buildings 110

Figure 9.4 Screenshot of software tool homepage 112

Figure 9.5 Screenshot of ‘Renovated building’ section of software tool 112

Figure 9.6 Screenshot of ‘Results’ section of software tool 113

Figure 9.7 Examples of typical renovation options reviewed 114

Figure 9.8 Ten renovation solutions implemented into the tool 115

Figure 9.9 Embodied carbon versus thermal transmittance for renovation options 116

Figure 9.10 Input interface 117

Figure 9.11 Graph showing renovation solutions comparison 118

Figure 9.12 SolarWall™ cladding on industrial building in Durham, UK 120

Figure 9.13 Installation of composite panels on industrial building in Scotland 120

Figure 9.14 Roof-top extension of university building in Rzeszow, Poland 121

Figure 9.15 Valtellina office building in Milan 121


13 LIST OF TABLES

Table 5.1 Key drivers for renovation of buildings 22

Table 5.2 Design criteria for over-cladding systems 26

Table 5.3 U-values of reference wall and double-skin wall according to concrete thickness and fixed insulation thickness (50 mm) 32

Table 5.4 Data for original and renovated office building 34

Table 5.5 Annual heating demand in Helsinki, London, Berlin, and Moscow 34

Table 5.6 Annual cooling demand in Helsinki, London, Berlin, and Moscow 35

Table 5.7 Heating energy demand (whole year, specific values, existing building with vertical extension) 35

Table 5.8 Annual cooling energy demand of renovated building and its vertical extension 36

Table 5.9 Key dimensions of the apartment building 36

Table 5.10 Data for original and renovated apartment structure 37

Table 5.11 Annual heating demand in Helsinki, London, Berlin, and Moscow 37

Table 5.12 Summary of summer 2008 monthly results from the thermal chamber 39

Table 5.13 Summary of winter monthly measurements in the central section of the wall 40

Table 5.14 Heat losses in the winter months 40

Table 5.15 Typical weather scenarios used to predict energy savings due to TSC cassette panels 50

Table 6.1 Regulatory requirements in Europe for envelope air-tightness in new buildings 57

Table 6.2 Building specification for thermal simulations 59

Table 6.3 Parameters for thermal analyses 60

Table 6.4 Default parameters for warehouse building areas 61

Table 6.5 Renovation or replacement of construction elements 64

Table 6.6 Parameters for thermal analyses of industrial building 65

Table 6.7 Results of thermal simulations using various weather data sets in the UK 66

Table 6.8 External wall construction of Building assembly “L” 68

Table 7.1 Drivers for renovation by building extensions 75

Table 7.2 Typical dimensional characteristics of residential buildings 77

Table 8.1 Results from LUSAS analysis for 8 m span Open Roof truss 92

Table 8.2 Typical chord and rafter sizes for the Open Roof System 94

Table 8.3 Residential building types analysed 95

Table 8.4 Data for thermal simulations 96

Table 8.5 Annual heating energy demand for various design cases 97

Table 9.1 Summary of BREEAM assessment 119


14 LIST OF ACRONYMS AND ABBREVIATIONS

ACH Air change per hour

DRL Driving rain leakage

EPD Environmental Product Declarations

ETICS External Thermal Insulating Composite System

FEM Finite element method

GB Gypsum board

IR Infra-red

LCA Life cycle assessment

PUR/PIR Rigid polyurethane and polyisocyanurate

PV Photovoltaic

RH Relative humidity

TSC Transpired solar collector

U-value Measurement of heat transfer through a given building material (also called thermal transmittance)

WP Work Package


15 REFERENCES

1 Demonstration of modular construction in the renovation of existing concrete and masonry

buildings, ECSC Project 7215-PP/010, EUR 20595, 2003.

2 Lawson R.M., Pedreschi R., Falkenfleth I, and Popo-Ola S.O. Over-cladding of Existing Buildings using Light Steel The Steel Construction Institute P-247, 1999

3 Hillier M., Lawson R.M. and Gorgolewski M. Over-roofing of Existing Buildings using Light Steel The Steel Construction Institute P-246, 1999

4 BMS Publication ‘Bouwen Op Toplocaties’,Bouwen met Staal, NL, 2002

5 Anderson J.M. and Gill J.R., Rain-screen Cladding: A guide to Design Principles and Practice, Construction Industry Research and Information Association, 1988

6 EN 15026 Hygrothermal Performance Of Building Components And Building Elements - Assessment Of Moisture Transfer By Numerical Simulation, 2007.

7 Conserval Engineering Inc., Case Histories at http://solarwall.com/en, 2009

8 Hart, D. Jaguar Land Rover Academy to save 19 tonnes of CO2 per annum with SolarWall. 2007 [cited 2009 13th May]; Available from: http://www.cagroupltd.co.uk/canews/building-products/jaguar-land-rover-to-save-19-tons-of-co2-per-annum-with-solarwall

9 Duffie, J. A. & Beckman, W. A., Solar Engineering of Thermal Processes, New Jersey, John Wiley & Sons, 2006

10 Gawlik, K. M. & Kutscher, C. F., Wind Heat Loss From Corrugated, Transpired Solar Collectors. Journal of Solar Energy Engineering, 124, 256-261, 2002.

11 Brunger, A. P., Kutscher, C. F., Kokko, J., Cali, A., Hollick, J., Mcclenahan, D. & Pfluger, R., Low Cost, High Performance Solar Air-Heating Systems Using Perforated Absorbers, International Energy Agency, 1999.

12 Kutscher, C. F., Christensen, C. B. & Barker, G. M., Unglazed Transpired Solar Collectors: Heat Loss Theory. Journal of Solar Energy Engineering, 115, 182-188, 1993.

13 Gunnewiek, L. H., Hollands, K. G. T. & Brundrett, E. (2002) Effect of wind on flow distribution in unglazed transpired-plate collectors. Solar Energy, 72, 317-325.

14 Conserval Engineering INC., SolarWall by Conserval Engineering Inc., Conserval Engineering Inc.,2009

15 Hollick, J.,Perforated unglazed collectors. In Morck, O. & Hastings, R. (Eds.) Solar Air Systems: A Design Handbook. London, James & James (Science Publishers), 2000

16 Delisle, V., Analytical and Experimental Study of a PV/Thermal Transpired Solar Collector. Mechanical Engineering. Ontario, University of Waterloo, 2008.

17 CLG (Communities and Local Government), National Calculation Methodology modelling guide (for buildings other than dwellings in England and Wales), Department of Communities and Local Government, London, Oct 2008

18 EN 13829 Thermal performance of buildings. Determination of air permeability of buildings. Fan pressurization method, 2001

19 EN 13187 Thermal performance of buildings. Qualitative detection of thermal irregularities in building envelopes. Infrared method, 1999


20 The Air Tightness Testing and Measurement Association, Technical Standard 1, Issue 2,

Measuring air permeability of building envelopes, 2007

21 http://www.buildingsciences.co.uk

22 http://www.2010ncm.bre.co.uk/

23 UK Building Regulations, Approved Document Part L (Conservation of fuel and power), 2006

24 EN 1991-1-4:2005+A1:2010 Eurocode 1. Actions on structures. General actions. Wind actions

25 CEN/TS 1992-4-2 Design of fastenings for use in concrete Part 4-2: Headed Fasteners, 2009

26 TRA, Creating Roofspaces with Trusted, Rafters Trust Rafter Association, Product Data Sheet No. 6, 2007

27 EN 12975-2 Thermal solar systems and components. Solar Collectors. Part 2. Test methods. 2006

28 Corus Confidex Sustain EPDs: http://www.colorcoat-online.com/en/products/guarantees/confidex_sustain/supporting_sustain_epds/

29 GaBi Professional LCI Database

30 Bath ICE, Inventory of Carbon and Energy, University of Bath, UK, 2008

31 Winter B.N., Hestnes, A.G.,Solar versus green: the analysis of a Norwegian row house. Solar Energy. 66(6): 387 – 93, 1999

32 Thormark, C., A low energy building in a lifecycle-embodied energy, energy need for operational and recycling potential. Build environment, 37 (4): 429 – 435, 2002

33 Dimoudi, A.; Tompa, C.,: Energy and environmental indicators related to construction of office buildings. Resources, Conservation and recycling, 53 Pages 86 – 95, 2008


APPENDIX A TECHNICAL ANNEX














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