l NEWS, VIEWS AND INFORMATION FOR CONSERVATION ENGINEERS Spring_Summer 2012-.pdf · News from our...

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newsletter NEWS, VIEWS AND INFORMATION

FOR CONSERVATION ENGINEERS

P15 THE HORNIMAN MUSEUM Recounts of subsidence caused by heat

P16 ST WILFRID’S CHURCHRepairs to an unusual roof

P18 FORTHCOMING EVENTSConservation events and competitions

P10 ENGINEERS IRELANDSupporting CARE

P11 DEWSBURY MARKET HALLConservation repairs

IN THIS ISSUE:

Spring/Summer 2012

complex operation with five huge roof trusses installed to replace the existing, heavily damaged beams that had led to roof collapse and water ingress. Internal birdcage scaffolding allowed these works to take place safely with a temporary external roof covering installed over the winter months.

Denise Bernard (formerly Devine) Chair/Trustee of The Florence Institute Trust Ltd said: “For years, the Florrie became a blight both visually and physically on the landscape for local people and after an arson attack left it considerably damaged it became clear that something had to be done. Some people wanted the Florrie to be razed to the ground but thankfully the appetite was there to save her.

“By the Spring of 2012 the Florrie will once again be playing a pivotal role in this vibrant and diverse community,” Denise added.

YorkTel: 01904 412 624Fax: 01904 413 535

ManchesterTel: 0161 223 7462Fax: 0161 230 6514

[email protected]

There can be no finer tribute to the energy, passion and community spirit of the people of Liverpool than the completed restoration of the Florence Institute in the Dingle area of the city.

Sited just yards from the River Mersey, the impressive grade II Listed building was built in 1889 as a tribute to Florence Hall, the daughter of former Liverpool Mayor Bernard Hall who died tragically at the young age of 22.

For decades the building served the people of Liverpool and is Britain’s oldest surviving purpose-built boys’ club. The Florrie finally closed her doors in 1988 and subsequently fell into disrepair.

York and Manchester based building restoration contractors William Anelay, a firm with 265 years experience was charged with the restoration work under the auspices of architects Purcell Miller Tritton LLP and Project Manager Buro Four on behalf of The Florence Institute Trust Ltd, set up by local residents in 2005.

The £4.8 million programme of works, which started in the summer of 2010 and completed in March 2012, was funded by the Heritage Lottery Fund in partnership of european, regional and local regeneration agencies, including the Northwest Regional Development Agency, and ERDF. The project has converted the former dangerously derelict and vandalised landmark into a thriving community resource and social comprehensive centre, with a well balanced community and commercial remit.

William Anelay, has carried the work out in two distinct phases, to achieve a ‘very good’ BREEAM rating. The first four month tranche of activity focused on initial enabling works to clear the building and make it safe enough for

the Project Design Team to safely gain access and assess for necessary repairs and alterations with William Anelay experts on hand to advise on technical issues.

The second phase of works began in earnest early in 2011 and included the complete repair of external brickwork and terracotta to all elevations, the construction of a new traditional lead and slate roof and the recreation and reinstatement of architectural features such as vents and the distinctive copper cupola that sits high above the existing entrance.

Internally the building was restored and reordered with extensive repairs to floors and walls and the installation of new mechanical and electrical services throughout.

Anelay’s Site Manager Gary Shea commented: “Arson and vandalism had taken its toll on the building and left it disused and structurally compromised for over two decades. There was a strong element of risk given the building’s perilous condition.

“The initial enabling works has paved the way for transforming the building back into a valuable community resource.

“The ground floor of the finished building comprises of a large 220m² gym facility with library, heritage centre café, kitchen and toilet facilities as well as a number of small business units.

“On the first floor there is a large 320m² main hall which will be used for functions with a stage lift constructed alongside associated bar facilities. There’s also a balcony area and steps up to the observatory upon which a new copper cupola has been restored.

“Restoring the main hall has been a

P15 THE HORNIMAN MUSEUMRecounts of subsidence caused by heat

IN THIS ISSUE:

P04 WELCOMEChairs notes

P11 DEWSBURY MARKET HALLConservation repairs

P05 ACCREDITATION UPDATENews from our partners

P10 ENGINEERS IRELANDSupporting CARE

P16 ST WILFRID’S CHURCHRepairs to an unusual roof

P18 FORTHCOMING EVENTSConservation events and competitions

The Conservation Accreditation Register for Engineers (CARE) identifies civil and structural engineers skilled in the conservation of historic structures and sites. Members have followed a rigorous approval procedure to confirm an appreciation of disciplines and interests extending well beyond their professional training as engineers. They have demonstrated that they are fully conversant with conservation philosophy and methods applied to heritage projects.

Additionally, CARE has been established to:

▪ Assist clients in selecting an appropriate engineer with proven

conservation experience

▪ Encourage education and training in conservation engineering

▪ Promote sympathetic and ‘best practice’ conservation

▪ Raise the awareness of conservation in the engineering profession

Those who are registered are listed on the CARE website and entitled to use the descriptor ‘Conservation Accredited Engineer.’

Further information, application forms and a list of registered members can be found at ice.org.uk/care

CAREThe Conservation Accreditation Register for Engineers

03 CARE NEWSLETTER Spring/Summer 2012 ICE.ORG.UK

THE CARE PANEL

Chairman

Jon Avent

Technical SecretaryClive Richardson

Panel MembersIan Hume, Terry Girdler, Lawrance Hurst, John Ruddy, Charles Blackett-Ord, Sarah Fray

Architect RepresentativesTony Walker, Bob Chittham, Tim Ratcliffe

RICS RepresentativeAmanda Watmore

Engineers Ireland RepresentativeRoseanna O’Leary

CARE Panel Regional RepresentativesWales, Cadw - Richard Turner Northern Ireland, NIEA - Manus Deery Scotland, Historic Scotland - David Mitchell

Institution of Civil Engineers Tony Blackmore Awards and Registers Executive t +44 (0) 20 7665 2102 f +44 (0) 20 7222 7500e [email protected] ice.org.uk/care

Over the past year the CARE Panel has continued to promote the register with the on-going support of the Institution of Civil Engineers and the Institution of Structural Engineers. With a stated objective of promoting accreditation within the engineering profession the Panel has sought to widen the opportunities for engineers working in the heritage sector. In response to this objective and also following approaches from engineers outside of the UK the first links have been formalised with Engineers Ireland, and their chartered engineers are now able to apply to join the CARE register and achieve the widely recognised accredited status.

I have been encouraged by the level of support given by ICE and IStructE together with Engineers Ireland in achieving this agreement and look forward to welcoming those engineers who have already expressed interest in submitting applications. The significance of this link-up should not be underestimated, as it recognises that building conservation needs to embrace local, national and international construction skills and techniques, and that having the ability to share knowledge and experience across a wider spectrum is to everyone’s benefit.

We only have to look at the on-going heritage loss in New Zealand and

the recent proposals to demolish Christchurch Cathedral to recognise the specific need for engineers across the world with highest possible standards of in-depth and wide ranging experience of traditional buildings and structures.

The New Zealand Historic Places Trust believes retaining both the cathedral and other heritage central city landmarks would help Christchurch’s recovery by reinstating cultural tourism. Having professionals with universally recognised experience of heritage structures can only assist with ensuring that all options are fully explored. With ICE and IStructE members practicing across the world these would be areas where we can, and should, encourage those working in the heritage and traditional buildings sectors to consider applying to join CARE. Options to forge links in a similar manner to that formed with Engineer Ireland should also be explored and encouraged; particularly now the first steps on this path have been successfully negotiated.

Jon Avent BSc(Hons) CEng MIStructE IHBCAccredited Conservation Engineer Chair CARE Panel

Chair NotesSpring/Summer 2012

04 CARE NEWSLETTER Spring/Summer 2012ICE.ORG.UK

CARE Panel Chairman

Jon Avent

NEW MEMBERSThe Panel are pleased to welcome our newest members of the CARE Register:

▪ Margaret Cooke

▪ Bridget Drake-Wilkes

▪ Jim Kerr

The principal construction professions of Architecture, Building Surveying and Engineering all have strong accreditation schemes that formally assess and approve an individual’s experience and competency working within the field of building conservation. The recent issue of the Home Countries Protocol on Accreditation is a formal acknowledgement of the need and benefits offered by recognised schemes and a welcome recent progression.

These accreditation schemes recognised by the UK’s principal conservation

organisations and in many instances have become a specific requirement for working on heritage projects.

The following pages provide an overview of the principal accreditation schemes operated for professionally qualified individuals working in the heritage sector. Whilst the IHBC scheme is different to the accreditation schemes operated by the principal professions of Architecture, Engineering and Surveying, it does provide a significant membership and skills base which is recognised across a wide range of built heritage professionals.

Accreditation UpdateOur partners


Criteria against which Accreditation Schemes would be considered by the Home Countries: Accreditation of individuals rather than companies or practices.The skills of a practice are only the combined skills of its individual members, and as individuals move, the skills of the practice will vary.

Eligibility of all suitably qualified and experienced professionals to gain accreditation.Schemes should be open to all members of the relevant professional discipline

Assessment of a verifiable record of work carried out.Accreditation needs to be a measure of experience and competence, so assessment cannot be based simply on a statement of philosophy or principles.

Assessment by suitably experienced, impartial assessors against agreed criteria.Peer assessment, together with reassessment on a regular basis (say every 5 years) to ensure that accreditation indicates current competence.

The use of the ICOMOS Guidelines for Education and Training in the Conservation of Monuments, Ensembles and Sites.These are agreed as the basis of assessment of candidates’ experience.

A credible ethical and linked disciplinary framework to ensure that standards are observed and maintained.There needs to be a way in which proper account is taken of examples of competence falling below the standards required by accreditation

Home Countries Accreditation Prorocol

THE CARE REGISTER

CARE is administered by the Institution of Civil Engineers (ICE) and the Institution of Structural Engineers (IStructE) and has been established to identify engineers skilled in the conservation of historical structures and sites, be they buildings, bridges, harbours, riverbanks, canals, industrial sites or natural landscapes. These engineers may either be working as lead consultants on projects where engineering is dominant or as sub-consultants where there is structural engineering content. They must have an appreciation of disciplines and interests extending well beyond their professional training as engineers and show that they understand the philosophy and methods applicable to the conservation of historic work.

The Register is intended as a means of encouraging engineers to raise their awareness and standards by pursuing their continuing professional development in this specialist field.

The RIBA’s Register of accredited conservation architects was launched in 2010. It enables those looking to commission work on heritage buildings to find architects with the specific skills and experience they require, encompassing all aspects of historic building conservation, repair and maintenance.

Recognising the distinctive nature of conservation work, and moving away from a ‘one size fits all’ approach, the Register operates upon three levels of membership, which also provide an incremental process of accreditation for those who are in the early phases of establishing their careers in building conservation:

▪ Specialist Conservation Architect (SCA): For those working on historic buildings of out-standing national importance, such as Grade I and II* listed buildings or scheduled

monuments, and with highly specialist skills in one or more aspects of conservation.

▪ Conservation Architect (CA): Suitable for those working on Grade II listed buildings, regionally important historic buildings and in sensitive historic environments.

▪ Conservation Registrant (CR): For those working on the repair, maintenance, alteration and refurbishment of heritage buildings, e.g. unlisted buildings in Conservation Areas, locally important historic buildings and the general pre 1919 building stock.

The RIBA Conservation Register is endorsed by English Heritage and Historic Scotland, who recognise the SCA level only for grant purposes.More information can be found on www.architecture.com


RIBA


The Register of Architects Accredited in Building Conservation is an independent accreditation body established in 1999 with the active support of English Heritage. The purpose of the Register is to protect the historic built environment from damaging interventions devised by people not skilled in historic building conservation and adaptation. It does so by publishing, for the benefit of clients, a register of architects whose work and skills in building conservation have been established by careful assessment.

AABC’s twenty assessment teams each comprise two accredited conservation architects and one lay person knowledgeable in the field and usually from a client background. Lay involvement in the accreditation process ensures the Register’s objectivity and client emphasis. Executive architects who personally devise and produce contract documentation and administer contracts make up the majority of the register and may use the suffix AABC (Architect Accredited in Building Conservation). Architects acting in more of an advisory or managerial capacity, perhaps leading several projects or acting as conservation officers but not personally producing

detailed documentation or carrying out contract supervision, may apply for accreditation as a consultant architect.

Similarly, specialist architects practising as conservators or researchers and having only a limited involvement in projects may also be accredited as a consultant architect. In this case registrants may use the suffix CAABC (Consultant Architect Accredited in Building Conservation).

There are over 400 architects listed on the Register. AABC’s website offers detailed guidance on core conservation principles, key competences and the preparation of applications for accreditation. AABC also operates an Apprentice scheme which offers a structured pro-gramme of mentoring and guidance to younger architects who wish to become accredited. Since the Register was established AABC has become a benchmark in historic building conservation. Membership has increased regularly over the last twelve years and continues to grow. More information can be found on www.aabc-register.co.uk

AABC

The RICS Building Conservation Accreditation Scheme (BACS) was established in 1992 to provide a register of individuals knowledgeable in the field of conservation of historic buildings or sites. Since its introduction the scheme has promoted good practice and standards and has gone on to become recognised and respected throughout the industry.

The aim of the scheme is to provide a register of individuals with experience and knowledge in the field of conservation of historic buildings or sites.

The scheme has the backing of English Heritage who will only select professionals form a number of approved bodies, RICS being one of these.

There are currently two routes into accreditation depending on educational attainment and experience.▪ Experienced – Only route for applicants with no posts graduate academic qualification in Building Conservation; or

▪ Academic – For applicants with experience and a recognised post graduate academic qualification in Building Conservation.

Members of the Building Conservation Accreditation Scheme are subject to ongoing monitoring by RICS Regulation. Accredited members of the Building Conservation Accreditation Scheme are required to provide details of continued involvement in building conservation on an annual basis by submitting details of their CPD records, and any additional documentation that may be required.

The register of fully accredited members is updated regularly and is available to the public and other client groups through RICS information services and the RICS Website.

More information of the scheme can be found on www.rics.org


RICS

Membership of the IHBC differs from other accreditation schemes as assessment concentrates on competence across conservation advice and processes. IHBC accreditation demands com-petent standards across the key stages of conservation: valuing and managing heritage, and where appropriate changing it for the better through intervention (illus). If applicants do not demonstrate competence in their primary discipline, they cannot satisfy the demands of IHBC accreditation.

Applicants are not expected to be experts across each stage of conservation, but must demonstrate competence outside their specialist area. The application process ensures applicants consider conservation skills holistically, acknowledging what they do not know as well as what they do. This satisfies the spirit of the 1993 ICOMOS guidelines as well as the letter. Also, applicants

might come from any discipline, but must also articulate and verify a high-level balance of skills, knowledge and experience across conservation, all to the satisfaction of an inter-disciplinary panel of assessors.

Unlike other professional bodies, the IHBC do not re-accredit members, but operate a disciplinary process tied to a Code of Conduct, that provides a continual monitoring of conservation standards in accredited members. Like others systems, the IHBC does not accredit businesses, but does ‘recognise’ them through a quality-assurance listing called HESPR. The services these businesses provide are tied to the IHBC standards through employees who are also IHBC accredited members.

IHBC: www.ohbc.org.ukHESPR: www.ihbc.org.uk/hespr/Contact: Sean O’Reilly, [email protected]

IHBC


The IHBC’s Conservation Cycle informs our accreditation as applicants must demonstrate skills across the cycle from valuing and management to, where appropriate, intervention.


Engineers Ireland Supporting CARE

With CARE providing the framework to promote engineering standards within the heritage sector and with growing recognition of the benefits of achieving formal accreditation it is a welcome and logical step for Engineers Ireland to provide its support to the register. Following the recent formalising of links with the register, Chartered members of Engineers Ireland are now eligible to apply to join the register by following the same application process open to chartered members of ICE and IStructE.

For those unfamiliar with Engineers Ireland, the working title for “The Institution of Engineers of Ireland” it traces its origins back to 1835 when a group of leading Irish engineers formed a society to promote the civil engineering profession and share their experiences. In 1844 the organisation became the Institution of Civil Engineers of Ireland and 33 years later in 1877 became one of the first chartered institutions in the British Isles. Cumann na nInnealtoiri (The Engineers Society) was founded in 1928 to advance the prospects and status of its members.

In 1969 the Oireachtas (national parliament ) passed the Institution of Civil Engineers of Ireland (Charter Amendment) Act, 1969 and following this the Institution of Civil Engineers and Cumann na nInnealtóirí merged to form the Institution of Engineers of Ireland, later rebranded as Engineers Ireland.

The new institution widened its scope to:▪ Cater for all engineering disciplines

▪ Ensure standards in the profession

▪ Promote engineering as a career

▪ Encourage Continuing Professional Development for engineers

▪ Represent the interests of the engineering profession in Ireland and internationally

Ireland has a rich and varied built heritage spanning many centuries. Throughout the country there are many building types and structures represented, some of which are unique to the country. This built heritage takes the form of large estate houses, vernacular heritage such as thatched cottages, industrial related structures such as canals, bridges, mill buildings and warehouses with planning authorities obliged to have a Record of Protected Structures (RPS). Owners and occupiers of protected buildings are required to ensure that buildings do not become endangered through harm, decay or damage. Having widely recognised professional conservation accreditation standards to support this process and provide the highest standard of advice is undoubtedly a benefit to all concerned. Engineers Ireland look forward to developing and growing strong links across the heritage sector through their support of CARE. Further details can be found on Engineers Ireland website at http://www.engineersireland.ie/care/

Restoration of Dunboy Castle by Cork based conversation engineers, Southgate Associates

John Power, Director General of Engineers Ireland and Sarah Fray, Technical Director of Institution of Structural Engineers signing formal agreement.

ICE.ORG.UK 11 CARE NEWSLETTER Spring/Summer 2012 ICE.ORG.UK

The cast-iron and steel framed Dewsbury Market Hall, which is owned by Kirklees Metropolitan Council and stands in Dewsbury Conservation Area, was erected in 1903 and 1904 to the design of local architect and borough engineer Henry Dearden (Associate Member of the ICE), by H E Hodgson & Co, Contractors.

The hall is a single-storey four-bay framed building comprising an array of cast-iron columns supporting a series of riveted steel plate-and-angle perimeter beams, and three intermediate lattice girders made from steel plates and angles spanning east-west at valley positions. The roof structure comprises a series of 45-degree duo-pitched tied-arch trusses made from steel plates, rods and angles such that they span north-south from the perimeter girders on the south and north sides and the intermediate lattice girders. The four roof bays are hip-ended, and the half-trusses for these are supported by the east and west perimeter girders. The plan shape of the building is approximately an equilateral rhombus, the overall lengths of each side being just over thirty metres. The height to the eaves is approximately 8.5 metres.

Lateral stability in the structure is obtained through gravity and nominal connections via the tapped location bolts between the roof structure and the column tops, assisted by cantilever action assumed to be available from the foundations. In practice, this is probably also assisted by the timber-framed glazing that exists

between the undersides of the perimeter girders and RSJs above shop-front level.During routine re-painting in 2006, severe local corrosion was discovered in concealed steelwork above a cast-iron stanchion in the north-east corner of the market hall. Intrusive inspection behind the decorative cast-iron box-castings above remaining perimeter column tops revealed that severe corrosion was present at all these locations. The interior column tops, which are not concealed by decorative castings, were found to be free of damaging corrosion. The expansive action due to this highly-localised corrosion had lifted the perimeter beams by up to 25mm, such that many of the tapped location bolts fitted through the bearing areas had failed in tension. At several column tops, the perimeter beam webs had failed causing beam sections to settle onto the glazed screens below. In addition, the bolts that secured the ends of the intermediate lattice girders to the east- and west perimeter beams had failed due to corrosion of the beam webs.

The cause of the corrosion was electrolytic action between the dissimilar metals. This was promoted by the damp and dirty conditions that prevailed behind the castings, aggravated because the column shafts had also been used to convey rainwater to the public drainage system. It is thought that the damage had been present for a long time.

PROJECT INFORMATION

Existing part-section through roof

Cleaned-up column top revealing necked location bolts

Decorative box-casting removed reveals lattice girder end bolts have failed

Dewsbury Market HallConservation repairsIan Andrew CEng MICE MIStructE, WYG Engineering Limited, August 2011

The design principle for permanent repair was to reinstate the function of the perimeter beams and to ensure their bearings on the tops of the columns would be even (by removal of eccentricity induced by corrosion). Various improvements to prevent further corrosion were specified, including application of a two-pack epoxy protective paint system and introduction of a contact-breaker barrier between the new UB bearing flanges and the existing column tops. This principle allowed a minimal intervention route to be followed so that as much of the original fabric could be retained as possible.

The worst-affected areas were shored immediately to prevent further settlement. The presence of Batley Beck culvert very close to the east side was taken into account in the shoring scheme. The shoring, which was extended to provide temporary support for all perimeter beams, included a device to allow the perimeter beam ends to be jacked up slightly if desired to permit accurate realigning and re-levelling following implementation of permanent repairs. The method of implementing these repairs as originally designed was to cut out the corroded parts of the perimeter beams where they pass over each column and replace them with short UB sections spliced to the remaining beam sections, thus reinstating the bearings. This work also reinstated horizontal continuity in the perimeter beams across the column tops. However, at the start of the work on site

it was decided that the new UB sections would be too heavy to install easily. Whilst maintaining the design principle, the detail was therefore amended using folded steel plate and angle sections assembled on site. This had a further advantage that jacking was not required as the components were able to be fabricated on site to suit the distorted shape of the perimeter beam. The disadvantage is that the perimeter beams have been left in their distorted positions, although this has minimal visual effect.

The tolerance gaps under the new bearings were grouted using a specialist cementitious mortar. The grout also ensured there will be no direct contact between differing metals (mortar is a non-conductor and is alkaline), thus providing passive protection against future electrolytic action. The box-casting pieces, which had been cut up to allow them to be removed for access, were bolted to the structure and the cut edges cold-stitched back together, thus completing the repair work.

Certain other minimally-intrusive repairs and alterations were also incorporated to improve the structural performance of the building. The scaffolded work area at roof level provided for general refurbishment work presented an opportunity to improve this public building’s resistance to accidental horizontal loading (noting the existence of cast-iron in the primary load path).


PROJECT INFORMATION

Detail of existing part-elevation of column top and perimeter beams

Cutting out corroded steel in perimeter beams

Detail of proposed repair to column top using UB

ICE.ORG.UK13 CARE NEWSLETTER Spring/Summer 2012 ICE.ORG.UK

PROJECT INFORMATION

New folded-plate splice delivered to site

New steel splice fitted up on existing column top

Completed repair awaiting grouting and painting

This was done by removing the considerable “slack” in the existing tie-chords between the feet of the roof arches (there had been insufficient provision for tightening the tie-chords originally), so making the connection between the roof structure and the column tops more positive. This was done by inserting a new longitudinal carbon-steel tie-rod at tie-chord level in each of the four bays of the roof so that the existing tie-chords could be alternately displaced sideways and locked off against the new tie-rods. The number of bolts tapped into the cast-iron of the column tops was also increased where space permitted, to improve general robustness at column-top level.

Kirklees Metropolitan Council recognised that the building, whilst not listed, is in a conservation area, and that it was unlikely that the local community would have accepted replacement of their market hall without such repairs. In addition to following the chief principle of working with historic buildings, viz. minimal intervention to the fabric of the building, a high degree of sustainability was therefore achieved during repair of the market hall.

Exterior view after completion

Project Statistics:Client:

Kirklees Metropolitan Council

Architect:

Aedas Building Surveying Limited

Structural Engineer:

WYG Engineering Limited

Main Contractor:

Richardson Projects Limited

Cast-Iron Sub-Contractor:

Casting Repairs Limited

Project Cost:

£1.2 million

ICE.ORG.UK15 CARE NEWSLETTER Spring/Summer 2012 ICE.ORG.UK

Clive Richardson, a Technical Director of URS, and their Conservation Team Leader, recounts the surprising case of subsidence caused by heat from a basement boiler room.

After 90 years of stability, part of the Horniman Museum in South London suddenly started to subside. Its heating system had baked the clay ground beneath it. This adversity was turned to advantage with underpinning to make new basement space. Top-down construction was used for temporary stability and to conserve the unique tiled ground floor.

The Horniman Museum was built in 1901 at Forest Hill in South London. Designed by Charles Harrison Townsend in the Art Nouveau style for the tea merchant, Frederick Horniman, it is now listed Grade II star. Behind its stone façade are two original exhibition halls with brick cladding, founded on concrete strip foundations, stepping up the shrinkable London Clay hillside.

The superstructure is distinctive for its use of all three metals: riveted wrought iron barrel-vaults, cast-iron balcony columns, and mild steel filler-joist gallery floors. The floors have mass concrete ground-bearing slabs with perimeter ducts which deliver heat through their floor gratings by convection from water pipes heated by basement boilers.

One day it was noticed that some of the tall glass exhibition cabinets in the south hall were tilting. Part of the floor and the column supporting the end balcony over it had sunk 100mm.

A trial-pit was dug through the floor, and we were greeted by a blast of hot air! The clay had shrunk away from the floor leaving a gap under the floor slab through which hot air was escaping from the heating ducts. Fortunately the basement heating of the north hall had been de-commissioned many years ago, so the problem only affected the south hall.

The clay had been baked as hard as brick to a depth of four metres. It had lost its clay-like properties. When a lump was placed in water, instead of re-hydrating and swelling, the clay disintegrated and collapsed to a powder. Indeed, the case was so singular that the Building Research Establishment offered their services free of charge.

There was concern that if the water table rose, wholesale collapse of the baked clay could occur, which would not just affect the floor slab, but also the foundations of the hall. It was decided to remove the baked clay, and rather than backfill the 4m deep excavation, the museum’s Trustees asked for a new basement to be created instead, as they were short of space.

Top-down construction was chosen, to maintain lateral stability of the existing shallow foundations. Mining techniques were used to burrow under the tiled ground floor between the south and north halls, and not a single tile was lost in the process.

As the museum had always been free and the Trustees had never sought funding, English Heritage gave them a 100% grant of £1.1m to do the work. “Free Museum” is still emblazoned in stone over its entrance to this day, and it is now free from subsidence too!

PROJECT INFORMATION

The Horniman MuseumRecounts of subsidence caused by heat

Trial pit through ground floor slab, revealing clay beneath baked like brick.

Heating ducts beneath the floor, dropped away from floor slab.

Cracked column casing, hanging from balcony above.

The churchSt Wilfrid’s is a Grade II* listed Anglican Church situated off Selby Road, Halton, Leeds, built in 1938 and designed by the arts and crafts architect A. Randall Wells.

The building is steel framed, with stanchions and concrete cased beams. The shallow pitched roof consists of steel trusses at 3m centres, spanning 9m across the Nave, Transept or Chancel. Between the trusses are corrugated asbestos sheets with infill reinforced concrete. The deck is then waterproofed with mastic asphalt.

Suspended from the trusses is a vaulted ceiling consisting of strawboard and plaster skim on a light steel frame.

The problemThe asphalt is reaching the end of its life and the roof has been leaking for some time. With asbestos present, it was undesirable to disturb, so over-roofing was proposed, using zed purlins, ply decking and either asphalt or a single ply membrane. Blackett-Od Conservation were engaged to advise on structural implications.

On-Site investigationsSince the over-roofing scheme represented an increase in load, it was necessary to check the existing roof structure for this addition. No drawings of the existing structure were available, so compact mobile elevated working platforms were used to inspect concealed structure through holes cut in the vaulted false ceiling. Some opening up was also carried out on the roof to check the asphalt thickness and deck construction.

Asbestos and concrete decking systemThe decking system was unusual, so it was

important to learn more.

Investigations revealed:

▪ The decking is a 3” deep corrugated asbestos system with concrete filled corrugations

▪ Each corrugation has two steel reinforcing bars, each of which consists of two 6mm diameter strands twisted together

▪ Below the corrugated asbestos is a flat asbestos soffit board, somehow bonded or fixed to the corrugated sheet above. We could see no physical fixings

▪ There were occasional transverse 0.5mm cracks in the flat soffit asbestos sheets which sounded hollow when tapped, calling into question the bond between corrugated and flat sheets

A desk study included contacting the ICE and IStructE libraries and the Civil Engineering Heritage Exchange (CEHX). The Civils library came up with a technical article from the Indian Concrete Journal of November 1943 and an advertisement from a publication called “Specification 1937”. It concluded the product was “Handcraft Reinforced Decking” manufactured by Universal Asbestos, Watford. The Indian paper gave load tables suggesting that the maximum span for the 3” deep section was 6 feet. Since we had 3” sections spanning 10 feet, this was of concern.Checking by calculation the 3” deep reinforced section, we found that strength was adequate, but deflection exceeded acceptable limits.

Roof truss analysisIn parallel to the investigations into the decking system, we needed to check the roof trusses for increased loads. The trusses were made with steel angles, bolted to steel gussets. There was some slight surface corrosion generally, although more serious


PROJECT INFORMATION

Truss and Soffit of Deck in Roof Void

Ceiling Support System in Roof Void

Cherry Picker for Opening Up Work

St Wilfrid’s ChurchRepairs to an unusual roofMichael Taylor BSc CEng MICE Conservation Accredited Engineer February 2012

ICE.ORG.UK 17 CARE NEWSLETTER Spring/Summer 2012 ICE.ORG.UK

PROJECT INFORMATION

External View from South East

Exterior View from South West

Truss corrosion at roof leak

Client:

Design Team:

Advice and Principal Grant:

The PCC, St Wilfrid’s Church, Halton

Andrew Boyce (Architect) of Ferry and Mennim, York Blackett-Ord Conservation Engineers (Structural Engineers)ohn Broomfield (Corrosion and Concrete Repair Specialist)Turner and Holman, York, (Quantity Surveyors) Mason Clark Associates (CDM Co-ordinator)

English Heritage

where the roof had leaked.

With the trusses made around 1938 we used figures from the Historical Structural Steelwork Handbook, taking a permissible bending stress of 8.0 tons/in2 (123.6 N/mm2) and compressive stress of 7.2 tons/in2 (110.7 N/mm2). Checks were done to BS 449 with a 5% section loss due to corrosion assumed. Calculations suggested 20% overstress in the bottom chord which could be eliminated by two simple additional ties per truss. Unfortunately access to the trusses would be difficult.

ConclusionsA dilemma existed. The over-roofing was possible and relieved the present decking system of superimposed load, thus minimising the deflection problem. Although the bond between sheets was questionable, there had been no historic failures and should such a failure occur, the vaulted ceiling below appeared robust enough to prevent any flat sheet falling. However, there were disadvantages:

▪ Possible future failure of the bond between asbestos sheets was undesirable

▪ It would be difficult to inspect and maintain the decking system and structure, which would be concealed from below and above

▪ Health issues with asbestos

▪ It would be difficult to properly inspect, repair, strengthen and paint the steelwork, which all were considered important requirements of the present scheme

The alternative was to remove the concrete and asbestos deck entirely replacing it with a simple timber joisted roof, thus eliminating the above problems and giving good temporary access for painting and repairing steel. However it would be expensive, particularly with the need to erect temporary scaffolding roof and devise a means of manhandling heavy deck units.

After much deliberation and discussion amongst the design team, the Church and English Heritage, it was decided to proceed with the decking removal.

Situation nowThe budget for Phase 1 of the work, which includes the Chancel roof, Aisles roof, repairs to Chancel windows, concrete repairs and other maintenance items is £650,000, excluding fees and VAT. Tenders have been received but as yet no contractor has been appointed. It is anticipated that the work will go ahead later this year, when we will endeavour to report further.

Acknowledgements:

Photographic CompetitionThe photographic competition which ran in the previous newsletter generated some confusion on eligibility for submitting entries. The only persons excluded from entering were members of the CARE Panel, effectively opening the competition to all others. To redress this, and to ensure those wishing to enter are given reasonable opportunity, it has been decided to award one book in this edition of the newsletter, and to extend the completion deadline to the 31st August 2012 for the remaining two publications on offer. All photographs currently submitted will remain open for consideration.

The Panel are pleased to confirm that the photograph selected from existing entries is The Mesquita, Cordoba, Spain submitted by John Watt.

This profoundly peaceful building is an 11th-Century Moorish mosque with a Baroque cathedral built through its centre after the retaking of Cordoba by the Christian Spanish monarchy. The building is a unique and enchanting blend of cultures and religions conserved to contrast these, at times, co-existing philosophies.


FURTHER INFORMATION

CompetitionTerms and Conditions

There is no specific guidance on the theme of photograph so we hope to receive entries showing the full spectrum of conservation, including the good and even ‘the bad’Maximum of three entries permitted per person.Photographs to be A4 size at 300 dpi resolution and in jpg format.Include a brief title and summary of the picture(s).By entering you are confirming that you hold the copyright of the photograph(s) and grant CARE, ICE, IStructE and Donhead PublishingLtd the right to use photographs in subsequent publicity.

Closing date for submissions is 31 August 2012.

The competition is open to all, with the exception of the CARE Panel.

Winning submissions will be notified by 30 September 2012, and will be published in the next edition of the CARE newsletter.

Forthcoming EventsConservation events and competitions

Forthcoming events

Date Event Location Contact18 June Historic Building Condition

SurveysRICS London http://www.rics.org

6 July Imagining conservation: the next twenty years

York Centre for Conservation Studies

[email protected]

3 - 6 Sept Conservation and repair of stone masonry

West Dean College [email protected]

9 - 13 Sept RICS and SPAB Building Conser-vation Summer School

Royal Agricultural College, Cirencester

[email protected]

24 - 27 Sept The structural repair of historic buildings


8 - 11 Oct Conservation and repair of timber


7 Nov COTAC Conference BRE Watford [email protected]

28 June SAVE Conservation book fair London www.savebritainsheritage.org

2 Oct Annual IHBC day conference London [email protected]

4-5 Oct Understanding wrought iron Malt Kiln Farm, Pentney

[email protected]

“The science of conservation”

We are a small, specialist building diagnostics consultancy based in Mid-

Devon, operating nationally.

Providing scientific assessments of timber decay and other damp related

building defects and advice on conservation-minded solutions for their

control.

We utilise non-destructive ultrasound and microdrill instrumentation to

assess the sub-surface condition of structural timbers. Tests quantify the

extent of decay, helping the engineer produce designs which minimise the

loss of historic timbers and surfaces.

Unlike chemical treatment companies, we are building conservation

professionals, who practise the philosophy of minimal intervention. We

focus on controlling defects by realigning environmental imbalances and

implementing repair strategies that embrace conservation principles.

Our in-house Works department provide practical assistance with

strategies for the control of wood decaying fungal infections and beetle

infestations.

We can be entrusted to administer targeted chemical treatments as

appropriate with projects including historic buildings, scheduled

monuments, ecclesiastical buildings and modern structures.

All our services can be undertaken at height utilising rope and powered

access solutions.

Exposure Surveying has a long history in building conservation and

undertake all projects with an environmentally responsible, ethical and

conservation minded approach.

Collating site dataProjects include historic buildings,

scheduled monuments,

ecclesiastical buildings and modern

structures.

Dry rot fruiting body, in sub-

floor space, seen through

borescope visual aid.

The microdrill assessing concealed

window lintels in a Grade II* property.

Ultra sound decay detection

equipment quickly assesses structural

timber.

01392 308 239

www.exposuresurveying.co.uk

[email protected]

The microdrill quantifies the extent of

decay

Rope access, proving a cost effective

alternative to traditional scaffolding.

Decay

Microdrill readings are displayed

at a 1:1 scale

Institution of Civil EngineersOne Great George StreetWestminsterLondon SW1P 3AA

t +44 (0)20 7222 7722f +44 (0)20 7222 7500

www.ice.org.uk

Registered charity number 210252.Charity registered in Scotland number SC038629.

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