Well designed concrete-intensive homes effectively balance the three dimensions of sustainability; social, environmental and economic. n The sound insulation properties of concrete walls and floors provide peace and quiet for a home, thereby improving its social amenity. n Concrete is inert, creating a healthy, low allergenic indoor environment. n The efficient thermal performance of a concrete-intensive home reduces energy demand, making the home more economical to heat and cool, and delivers significant greenhouse gas reductions. As the land available for homebuilding becomes increasingly scarce, and the size of house lots becomes smaller, we are forced to build our homes closer together and nearer noise sources such as highways and railways. This document outlines why concrete is the responsible choice for creating quiet, comfortable and sustainable homes. 16 JAN 2011 Quiet and Comfortable Concrete Homes Briefing
Transcript
Well designed concrete-intensive homes effectively balance the three dimensions of sustainability; social, environmental and economic.
n The sound insulation properties of concrete walls and floors provide peace and quiet for a home, thereby improving its social amenity.
n Concrete is inert, creating a healthy, low allergenic indoor environment.
n The efficient thermal performance of a concrete-intensive home reduces energy demand, making the home more economical to heat and cool, and delivers significant greenhouse gas reductions.
As the land available for homebuilding becomes increasingly scarce, and the size
of house lots becomes smaller, we are forced to build our homes closer together
and nearer noise sources such as highways and railways. This document outlines
why concrete is the responsible choice for creating quiet, comfortable and
sustainable homes.
16j a n 2011
Quiet and Comfortable Concrete Homes
Bri
efing
Page 2 Briefing 16 january 2011
Sound Reduction
Sound sourcesSound can be split into two broad categories – airborne sound and impact sound.
airborne sound consists of successive pressure waves or vibrations which are generated from a source such as speech or loudspeakers; and transmitted through the air. They cannot travel through walls or floors, but set up vibrations in them. The vibration of these elements causes the air on the other side to vibrate; it is these new airborne vibrations that are detected as transmitted sound. In broad principle, the greater the mass of the wall or floor, the more difficult it is to set up vibrations in it; and hence more difficult to transfer sound from one side to the other. Due to their mass, concrete walls and concrete floors perform well in reducing the transmission of airborne sound.
Impact sound is caused by objects striking the wall or floor. Examples include footsteps, objects dropped on floors, movement of chairs and possibly some appliances. The vibrations set up in a wall or floor from impact tend to spread out over the entire element and other elements connected to it. These vibrations result in vibrations in the adjacent air (airborne sound) or vibrations in objects attached to, or resting on, the wall or floor.
terminology used to describe sound reductionairborne sound is transmitted over a range of frequencies. In order to conveniently describe its attenuation (reduction) as a single index, it must be compared to sounds consisting of a series of standard frequencies. The weighted mean of the sound transmission losses, over an audible range of frequencies, gives a good indication of sound attenuation for walls and floors. The Weighted Sound Index (rw) for laboratory measurements is defined in aS/nZS ISO 717-1.
although a weighted index, such as rw, can predict attenuation of audible frequencies, some particularly low frequencies, such as urban traffic noise, are not well accommodated.
a Spectrum adaptation Term (Ct r) further describes the performance when subjected to sounds likely to originate from a-weighted urban traffic noise. The Spectrum adaptation Term is also defined in aS/nZS ISO 717-1, and has a negative value, such that when it is added to the rw, it reduces the combined value. Therefore relatively low values for Ct r indicate good overall performance at low frequencies, while high values of Ct r predict poor performance.
Corresponding terms, used to describe impact sound attenuation, Ln,w and C1, are also defined in ISO 717-1.
BcA requirementsThe BCa (Building Code of australia) gives the minimum sound insulation performance requirements for walls that separate attached Class 1 buildings and for the walls and floors that separate sole-occupancy units in Class 2 and 3 buildings and Class 9C aged-care buildings.
For example, BCa Volume 1 Part F5 set out the following requirements. Walls that separate sole occupancy units in a Class 2 or 3 building or between two Class 1 buildings shall have rw + Ct r (airborne) not less than 50 and impact sound resistance if the wall separates a habitable room in one sole occupancy unit from a bathroom, sanitary compartment, laundry or kitchen of another unit or plant room or lift shaft). Walls requiring impact sound resistance shall consist of two leaves separated by a gap of at least 20 mm or be connected by resilient ties. Designers should refer to the BCa Volumes 1 or 2 as appropriate, for other requirements.
The simplest path to compliance with these performance requirements is to adopt one of the DTS (deemed-to-satisfy) provisions given in BCa Volumes 1 and 2 for walls and floors.
For example a 150-mm-thick plain off-form concrete wall is deemed to have rw ≥ 50 dB and rw+Ct r ≥ 50 dB.
The same compliance may be achieved using a 125-mm thick concrete panel with a row of 64 mm steel studs at 600 mm centres, spaced 20 mm from the concrete panel, with 70 mm polyester insulation (density 9 kg/m3) between the studs and one layer of 13 mm plasterboard fixed to the outside face of the studs.
a 200-mm-thick concrete slab with carpet on underlay will satisfy airborne and impact sound require-ments by providing rw ≥ 50 dB, rw+Ct r ≥ 50 dB and Ln,w+C1 ≤ 62 dB.
Sound attenuation or reduction increases as the concrete thickness increases. Other combinations are set out in the DTS provisions of the BCa; and test data is available for still further forms of concrete wall and floor construction.
Determination of rw for 150-mm-thick concrete wall
Sound level spectra to calculate the spectrum adaptation term Ct r (from aS/nZS ISO 717.11)
Frequency (Hz)
Sum of differences ateach frequency ≤ 32 dB
R (d
B)
0
100
125
160
200
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
10
Reference curve
20
30
40
5054
60
70
80
Test results curve
Frequency (Hz)
L ij (
dB)
–25
100
125
160
200
250
315
400
500
630
800
1000
1250
1600
2000
2500
3150
–20
–15
–10
–5
0
Briefing 16 january 2011 Page 3
theRmAl comfoRt
thermal massThe comfort of occupants is a primary function of a building and a major determinant of the material used for the building envelope and of its form. The thermal mass of solid concrete can be used to reduce the energy required for space heating or cooling to maintain satisfactory occupancy comfort.
Thermal mass (also called thermal capacitance or heat capacity) is the capacity of a body to store heat. It is designated by C, and typically measured in units of Mj/m3.K or Mj/t.K; or the Celsius equivalent Mj/m3.°C or Mj/t.°C. Dwellings with a medium to high level of thermal mass are characterised by their inherent ability to store thermal energy, and then release it several hours later.
Concrete elements possess a natural advantage in heat storage capacity, resulting from the combined effect of the nature of the material and the volume of concrete required to construct the
slabs, columns, beams, stairs, roofs and the like. When used in passive solar design, the thermal mass can make large positive contribution to reducing energy consumption, while maintaining the occupancy comfort.
In summer, concrete elements act as a heat sink, absorbing heat from the occupants and appliances. a concrete building reacts slowly to outside temperature fluctuations, reducing dependence on energy for cooling to produce a comfortable internal temperature. Provided that the climate is such that the nights are cooler than the comfort level, the cool night air can ventilate the building and purge the accumulated heat that is emitted from the concrete building fabric.
During winter, when heating is required, the thermal mass will help keep a dwelling warm and reduce heating energy consumption. The operating principle is effectively the same as for the summer, except that solar gains are encouraged through appropriate glazing on a north-facing facade. Provided that the climate is such that the days are warmer than the comfort level, heat is absorbed by the thermal mass during the day and then slowly released at night. This is the same as for summer nights, the only difference being that during the winter this is useful heat, with windows and openings kept shut to minimise heat loss.
Thermal mass helps prevent a house overheating or getting suddenly cold when the heating or cooling plant cycles on and off throughout the day. It also helps
keep the house cool in the summer and warm in the winter, contributing to year-round comfort.
using concrete’s thermal massConcrete can be used in dwellings as floor slabs, wall panels, structural elements – such as beams and columns – or interior features such as bench tops and stairs. Its use in floor slabs has the biggest impact on thermal performance since most of the sunlight passing through the windows falls on the floors.
Concrete slabs are now often polished and left exposed; this is ideal for thermal performance. If a slab is to be covered, materials with good heat-conducting properties (eg quarry tiles, slate) should be used. If most of the floor receives winter sunlight there is some advantage in dark colours. Elsewhere, lighter colours are beneficial in order to maximise the reflection of sunlight onto other heat-absorbing elements.
The edges of the slab-on-ground floor, especially the northern edge, should be insulated to reduce the heat loss to the earth. Thickening of the slab to the depth of 250 mm in a two-metre-wide strip along this northern edge and insulating the outer face of the internal masonry leaf of external walls may also be considered. The large areas of glazing provided to allow winter sunlight to reach the interior should be protected from summer sun (eg by appropriate eaves overhangs).
In summer, concrete slab-on-ground acts as a heat sink. The floor slab benefits from the earth’s Direct gain – cooling cycle
Eaves shade glassfrom high-angledsummer sun
Open windows allow cross-ventilation
Concrete floor temperature modified by cool, deep-earth temperature
Heavy-weight walls (of concrete panels or masonry)and concrete floor, absorbheat from internal air
Disclaimer: Cement Concrete & Aggregates Australia is a not for profit organisation sponsored by the cement, concrete and aggregate industries in Australia to provide information on the many uses of cement, concrete and aggregates. This publication is produced by CCAA for that purpose. Since the information provided is intended for general guidance only and in no way replaces the services of professional consultants on particular projects, no legal liability can be accepted by CCAA for its use.
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ISSN 1837-5782
16j a n 2011
durable and secureGood quality concrete has excellent durability. unlike some other materials, concrete does not rot or rust, thus it requires very little or no maintenance throughout its life cycle. Housing stock built with concrete components such as wall systems can stand for generations. Concrete is less susceptile to moisture damage as it is naturally waterproof but allows the passage of vapour. This enables the building to breathe and dry – if the concrete structure is not too close to adjacent structures.
Concrete is a strong material with good wear and vandal resistance. Concrete driveways will far outlast those of asphalt, and will not be prone to the deformations often experienced in segmental driveways.
Compared with metal or timber cladding materials, concrete panels outperform due to their superior strength and durability. By simply outlasting other materials, concrete conserves energy and resources.
In addition, homes built with concrete are more likely to subject to tighter engineering design and construction supervision, resulting in structures more likely to withstand natural disasters such as hurricanes, tornadoes, floods and fires than traditional timber-frame houses.
concrete – the responsible choiceThe sound insulation features and thermal mass of concrete, together with other beneficial properties, provide better comfort, lower energy consumption and lower construction and operational costs. Concrete is the responsible choice to meet the requirements of sustainable development through balanced social, environmental and economic outcome.
near-constant low temperature. When concrete internal walls and insulated concrete external walls are also used, the total heat storage capacity of the house makes it react slowly to outside temperature fluctuations, reducing dependence on energy-hungry cooling equipment.
For optimum performance in summer, it is vital to provide cross-ventilation in a building to not only supply fresh air but also to:
n give instantaneous cooling whenever the inside temperature is higher than that outside;
n remove overnight the heat stored in the building fabric during the day (commonly referred to as night purging);
n accelerate the evaporation of moisture from occupants’ skin, thereby improving comfort (this can also be provided by the use of fans, particularly ceiling fans).
healthy livingConcrete can promote a healthier indoor atmosphere because it is practically inert and requires no volatile organic-based preservatives. Good quality concrete is naturally water and fire resistant, therefore not needing special coatings or sealers. Concrete can be easily cleaned with organic, non-toxic substances.
The continuous layer of concrete within the walls makes them exceptionally airtight. air flow through solid concrete is negligible, so drafts are eliminated. This greatly reduces the level of airborne dust and allergens when a fresh air exchanger and humidifier are used. In tests, houses built with concrete walls typically had one-third to one-half as much air infiltration as a typical timber-frame house.
Concrete houses incorporating passive solar design principles can provide more-stable internal temperatures, thus minimising the need for mechanical heating and cooling, which in itself results in good indoor air quality and promotes healthy living.
BiBliogRAPhy
n Sound Insulation Properties of Concrete Walls and Floors Data Sheet Cement Concrete & aggregates australia, 2009.
n Building Code of Australia Volume 2, Building Code Board, 2010.
n Passive Solar Design Briefing 09 Cement Concrete & aggregates australia, 2003.
n Comfort and Quiet with Concrete Homes Concrete Homes Technology Brief, no. 6, Portland Cement association, www.cement.org.
n Climate-responsive House Design with Concrete (T58) Cement Concrete & aggregates australia, 2007.
n aS/nZS ISO 717-1 Acoustics – Rating of sound insulation in buildings and of building elements – Airborne sound insulation, Standards australia 2004.
