12 AP r 2010

Thermal Mass Benefits for Housing Briefing

Thermal mass is the ability of a material to absorb and store heat. Concrete's high thermal mass, as part of an integrated passive solar design approach, can significantly reduce heating and cooling energy requirements and the associated green house gas emissions. It makes economic sense for householders to invest in a thermally comfortable home that will provide cost savings for the rest of its life. This Briefing demonstrates that concrete is the responsible choice for energy efficient and sustainable homes.

Introduction in some climates, eliminating altogether the Global warming is widely recognised need for heating and cooling systems. as a significant threat to our on-going Environmental life cycle studies have wellbeing; and there is a world-wide effort demonstrated that the majority of energy to reduce greenhouse gas emissions, the used in a house is consumed during its principal cause of global warming. Building operational phase1. Space heating and sustainable energy-efficient housing is one cooling to provide comfort conditions of the ways to effectively address global is one component of energy household warming, with the added benefit of reducing consumption. Recent studies2 show that heating and cooling costs. Using concrete’s almost eight in ten dwellings across Australia high thermal mass (as part of an integrated are artificially heated. There has also been passive solar design approach) can a substantial increase in the number of significantly reduce energy consumption and households with air conditioners. the associated CO2 emissions by reducing or, Electricity produced by coal-fired Internal temperature Internal temperature External with high thermal mass with low thermal mass temperature power stations is the main source of energy for household heating and Peak temperature cooling in Australia. In the two-year Up to 6–8°C difference delayed by up to between peak external period ending in 2010, the cost of six hours and internal temperature electricity has risen 20% on average 30°C across Australia3. An additional rise, as much as 60% in some states, is expected over the next three years4. The health and comfort of occupants are primary objectives of any house design. The thermal mass of solid concrete 15°C elements in a house can be used to reduce energy consumption Day Night Day for space heating or cooling, while maintaining a comfortable Figure 1 Stabilising effect of thermal mass on internal temperature 5 environment. Concrete can be (Source: Thermal Mass Explained The Concrete Centre ) used for internal and external gains are encouraged through walls, slab-on-ground and, in multi- Heavy-weight walls of storey dwellings, suspended floors. appropriately specified windows concrete panel or masonry A house using well established on a north facing facade. Heat is passive solar design principles, will absorbed by the thermal mass Concrete floor slab use less energy, and result in less during the day, and then slowly greenhouse gas emissions during released at night. This is the same its life cycle, when compared with as for summer nights, the only difference being that, during winter, Damproof houses built of low-thermal-mass membrane lightweight materials. this is useful heat, with windows This Briefing outlines how kept shut to minimise heat loss. Building-grade polystyrene board protected with fibre-cement sheeting concrete’s thermal mass can be Thermal Mass in Heating utilised in house designs to create a Concrete can be used in dwellings Figure 2 Slab-edge insulation in comfortable thermal environment all as floor slabs, wall panels, structural severe cold climate areas year round, in summer and winter. elements—such as beams and Principle of Thermal Mass columns—ceiling soffits or as Insulate outer face of heavy-weight Thermal mass (also called thermal interior features—such as cabinet, (concrete wall panels capacitance or heat capacity) is bench tops and staircases. or masonry) internal leaf. the ability of a body to store heat. The benefit of concrete floor Insulation materials such as styrene-foam It is designated by C and typically slabs is particularly apparent in board or single-sided measured in units of MJ/m3K or winter, as most of the sunlight, External Internal reflective-foil laminates, leaf leaf should be installed in MJ/tK or the equivalent MJ/m3°C entering through the windows, accordance with falls on the floors. If the slab is to manufacturer's or MJ/t°C. instructions Dwellings with high thermal mass be covered for aesthetic reasons, are characterised by their inherent materials such as quarry tiles, slate

ability to store thermal energy, and or vinyl with good conductance INTERIOR then release it several hours later. should be used on those parts of In summer, heat is absorbed on the floor receiving direct sunlight. Figure 3 Insulation of cavity wall in hot days, preventing the internal Increasingly, concrete floor slabs severe cold climate areas temperature from rising excessively. are being left exposed (and Provided that the climate is such typically polished.) If the concrete that the nights are cooler than the is coloured, dark colours permit the comfort level, the cool night air can solar energy to be absorbed directly ventilate the building and purge the into the concrete. While mid-range accumulated heat that is emitted coloured materials will reflect some from the concrete building fabric. of the solar energy—this may be During winter, when heating is an effective way of distributing it to required, the thermal mass is used other thermally massive surfaces, to help keep the dwelling warm and such as walls elsewhere in the to reduce heat energy consumption. direct-gain space. Carpets or The principle is effectively the same rugs should not be used on slabs as for summer, except that solar receiving winter sunlight.

Page 2 Briefing 12 april 2010 The edge of a slab-on-ground air is circulated by fans, particularly LIFE CYCLE ASSESSMENT floor, especially the northern edge ceiling fans, it can rapidly assist in STUDIES that acts as the prime heat store, achieving comfort conditions. A true indication of the sustainability should be insulated to reduce the Solar shading should be of building materials and buildings heat loss to the ground. (When configured over northern windows can be achieved only by consider- using edge insulation, designers so as to minimise the amount of ation of both the construction phase should consider the appropriate summer sun reaching the interior. and the operational phase of the means of providing for termite Further protection by means of a building, over its whole service life, inspection). Thickening the concrete pergola covered with deciduous ie a Life Cycle Assessment. slab to a depth of 250 mm in a vines or adjustable fabric or metal A Life Cycle Assessment (LCA) two-metre-wide strip along the blinds on the north-facing windows examines the environmental impact northern edge, and insulating the is also desirable. This protects of a system throughout the whole of outer face of the internal masonry the windows from heat gain in its life, ie from the time the resources leaf of external walls may also be unseasonably hot weather occurring are removed from the ground to the considered Figures 2 and 3. in early autumn or late spring. time when they are retrieved at the As the outside air temperature end of the system's life. It must also Thermal Mass in Cooling increases during a summer day, the include consideration of the effect In summer, a concrete slab-on- walls and floor absorb heat from the that the particular building system ground acts as a large heat sink, outside air and delay the rise in the has on the operational (heating and benefiting from the ground’s internal-air-temperature. Additional cooling) energy. Cement Concrete & near-constant low temperature. measures include: Aggregates Australia commissioned When concrete internal walls n Foster vegetation near southern a series of case studies to be and insulated concrete external and side openings. If these conducted by the then Department walls are also used, the total heat plants are watered in summer, of Public Works and Services storage capacity is enhanced. The the air passing through them will (DPWS) of NSW to demonstrate the house reacts slowly to outside be partly cooled before entering use of LCA as a tool for assessing temperature fluctuations, and there the internal space. and comparing whole buildings over is thus a reduced dependency on n Plant deciduous trees or vines on their entire life cycle. Details can be mechanical cooling to produce a the northern and western sides found on www.ccaa.com.au1. comfortable internal temperature. of a building to provide shade Five case studies were To maximise the benefits of in summer and admit sunlight in conducted with a range of materials the cooling cycle in summer, winter. for floors, walls and roofing as good cross-ventilation should be n In sub-tropical and tropical humid shown in Table 1. provided. If the night-time external zones, and in humid areas of other The following assumptions were air temperature is lower than the zones, provide a ventilated space made in conducting the study: comfort level, air flowing though the between the roof and ceiling. n Four occupants (two adults and building will remove the heat stored n Add suitable insulation under the two children). in the building fabric during the roofing material. n User waste is recycled in day. This is commonly referred to accordance with local council as 'night purging'. When this cooled practices. n On-site construction waste where possible was sorted and Reflective foil sarking Insulated ceiling recycled in accordance with local council practices.

Open windows allow n Lighting and other electricity use cross-ventilation 7500 kWh. (This is an average calculated from data on the Ministry of Energy's website – www.doe.nsw.gov.au/doenew/ neww/Statistics/spdstats/index.

Heavy-weight walls html for energy use statistics). (of concrete panels or masonry) n All electricity is grid connected. and concrete floor, absorb Eaves shade glass heat from internal air n Location: Sydney 'Climate Zone 6'. from high-angled summer sun The best performing was Case 4, Figure 5, with concrete slab-on-ground, tilt-up walls with Concrete floor temperature modified by cool, deep-earth temperature plasterboard lining, timber battens and concrete-tile roof. In this case, Figure 4 Concrete floor temperature modified by cool, deep-earth the total heating and cooling energy temperature was about 30% lower than Case 1.

Briefing 12 april 2010 Page 3 Table 1 Construction details of five case studies 7000

Case Floor External walls Internal walls roofing 6000

1 Timber Timber/stud/ Plasterboard Pre-painted steel 5000 plasterboard roof

2 Concrete Brick veneer Plasterboard Terracotta tiles 4000 slab on ground 3000 3 Concrete Double brick Rendered Concrete tiles slab on ground cement brick 2000 4 Concrete Tilt-up panel Tilt-up panel Concrete tiles slab on ground with plasterboard 1000 and battens

kWh/year 0 5 Concrete Tilt-up panel Tilt-up panel Concrete tiles Case 1 Case 2 Case 3 Case 4 Case 5 slab on ground Figure 5 Annual heating and cooling

When other eco-indicators are position in the sky to appear higher When glass is oriented to the considered, there are even more at noon in summer than in winter, north, it is essential to provide an significant differences. and daylight to extend for a longer eaves overhang that allows sun These studies indicate that period in summer. penetration in winter, but excludes the energy used to produce the Building orientation should it in summer. The extent of this construction materials (embodied account for the location of a site, overhang can be easily calculated energy) is generally less than 20% of the sun’s altitude (which varies with according to location, using the the operational energy used over a latitude), and the position of true eaves overhang design chart in fifty-year life. The operational energy north. This causes a variation in Passive Solar Design 7. It is also demand thus has a much more the angles of sun penetration into a essential to ensure that plenty of significant impact on the overall room. There are many publications sun can reach the glass in winter, energy usage—and therefore on the that elaborate on this point, including and that it is not obstructed by environmental impact—than does CSIRO Technical report No. 92/2 6. vegetation or neighbouring property. the embodied energy.

Optimising the Benefits of Thermal Mass Designing to take advantage of thermal mass requires an integrated approach, where the interaction between the main components of the dwelling are evaluated to find the best overall balance of orientation, glazing and use of concrete elements. Orientation Residential buildings, designed to capitalise on the benefits of solar energy, should be planned with living areas placed to admit the sun in the cooler months. The key to a house that is naturally warmer in winter and cooler in summer is consideration of the earth’s diurnal rotation about its axis and the tilt of the earth’s axis in relation to its orbit around the sun. The diurnal rotation causes the change from night to day, and the tilted axis Figure 6 Climate zones based on temperature and relative humidity produces summer and winter. (Building Code of Australia) These phenomena cause the sun’s

Page 4 Briefing 12 april 2010 Cold winds Trees to shield against wind

Solar heat gain in winter Deciduous (thermal mass) shade trees Pergola

Wall to shade against late summer sun

B B F

Creepers on wall B

K D L carport

Figure 7 Planning for temperate climates

Design for climate A thorough knowledge of the is then considered. In temperate For the comfort of occupants and micro-climate of a particular site, climates, living spaces should be for energy efficiency, houses should the direction of cooling summer placed along the north face of the be designed to suit the particular breezes, cold winter winds, building. Least occupied spaces— climate at its location. Australia has wind‑borne dust, etc is required. such as storage areas, circulation a diverse range of climate zones, areas and garages—should be Planning Figure 6. These vary from tropical placed along the south, where In temperate climates, buildings that regions in the north, through the they act as a buffer between living are longer in the east-west direction, arid expanses of the interior to space and the cooler south facing rather than in the north-south temperate regions in the south. Most wall. Rooms that may benefit from direction, are more efficient for both Australians live near the wetter more morning sunlight, like bedrooms, winter heating and summer cooling. moderate south eastern coasts, bathrooms or kitchen areas, should This planning allows for maximum primarily in major cities. be on the east wall. However, glazing to the north and minimum For tropical areas such as children’s bedrooms can benefit east-west exposure to morning and Darwin, focus is on the control from northern sunlight if they are afternoon sun, Figure 7. of radiation and the dissipation to be used extensively for play or This does not mean that all of heat. For sub-tropical areas in study. Attention should always be buildings must be so planned. summer, a similar concept to that given to particular local climatic Different building solutions can cope for tropical areas is appropriate conditions. with the particular conditions of each with some passive heating for the site. These include the building Walls and windows winter season. Passive solar design shape, number of levels, and Internal walls can add substantially concepts are particularly suited effective glazing, including the use to the thermal mass of a building. to the temperate and arid zones. of clerestory windows and roof lights, External walls should provide Adelaide, Hobart, Melbourne, Perth, combined with adequate shading. insulation, surrounding thermally Canberra and Sydney lie within Hot arid climates demand high massive internal elements. warm, mild and cool temperate thermal mass construction, with Windows required for light and zones. Comprehensive guidance on the ability to night purge with cool ventilation also play an important house design for each climate zone breezes and cross ventilation to role in the collection and retention can be found in Climate-Responsive re-charge the thermal mass for of solar radiant energy. However, House Design with Concrete 8. the following day. Sub-tropical they should be treated differently The climate can vary dramatically humid climates demand a focus on depending on their orientation. within one climate zone, depending cross-ventilation, particularly in the n Windows in north-facing walls on the latitude and whether bedrooms, Figures 8, 9 and 10. have the greatest potential the location is coastal, alpine exposure to sunlight and can, (mountainous) or arid (desert). Interior spaces when combined with heat- The climate can also vary markedly When the location, general absorbing interior elements, from one valley to the next, by orientation and shape of the benefit most from winter sun. the orientation of a slope or by building have been decided, the However, they must be provided the effect of prevailing winds. organisation of interior spaces

Briefing 12 april 2010 Page 5 with appropriate sun-shading devices, such as eaves over- Extract ventilation hangs, to allow winter sun penetration while excluding summer sun.

n Full-height glazing in the northern cross-ventilation wall of a house may be provided by sliding glass doors opening Sunlight onto a patio or veranda. n East-facing walls may have a few windows intended to catch Natural light cross-ventilation morning sunlight that can be pleasant in any season in a temperate climate. However, north-east orientation should Figure 8 Ventilation strategies be used judiciously, as it is a potential source of excessive Courtyard walls screen solar gain in summer months. against wind and dust n South-facing walls never

get useful direct sunlight in Outdoor living temperate Australia. Therefore, south walls should have only Pergola with adjustable the minimum window area shading

required for lighting, ventilation, Massive Small windows and to admit cooling summer construction breezes. Alternatively, if there K D L are significant views to the south and large windows are wanted, double glazing should be considered. Courtyard for Sliding doors evening use for breeze n West-facing walls should also have minimal window area, and

should be protected (eg with Lightweight external awnings or deciduous Garage B B B construction vegetation) from the low summer afternoon sun.

n In temperate and cold climates, Garage shades wall all openings in walls (windows, from late afternoon sun doors or any other penetration) should be sealed around their Figure 9 Planning for hot arid zones perimeter to prevent seepage of air (infiltration). Because of Concrete Options insulated, the insulation should be their frequent use, the front and General located below the slab. The simple rear entry doors deserve special It is important that the distinction rule is that, as far as practicable, consideration. Infiltration around between the thermal mass the surface of the concrete should the frames may be controlled and the structural weight of an be left thermally exposed, eg by with self-adhesive sponge or element is understood. It does using finishes such as paint, tiles, mohair strips and a draught- not necessarily follow that a or plaster. The presence of internal excluder bar at the threshold. By heavyweight construction will finishes such as plasterboard recessing entry doors, protection automatically provide a high level and carpet (particularly with against prevailing winds of thermal comfort – this depends underlay) will, to some extent, act improves the performance of the on the extent to which the elements as an insulating layer and reduce door sealing. The planning of a can thermally interact with the available thermal mass. small enclosed space or entry occupied space, ie exchange heat vestibule may be considered to Ground floors with the internal environment. This act as an air lock, preventing Provided there is no insulation relationship is known as thermal further losses, especially in cool below a concrete slab-on-ground, linking. It is therefore important that temperate climates. For rear it will act together with the ground, the insulation in external walls be doors, a laundry may provide this at near‑constant temperature, to behind the concrete inner leaf (eg vestibule space. provide enhanced thermal mass. in the cavity). If ground floors are

Page 6 Briefing 12 april 2010 Trees to shield from wind

Vertical shading

Bulk-insulated wall L F

Bulk-insulated Privacy screen Ceiling fans wall

D K Carport B B B

Opening panels or louver walls for cross-ventilation

Figure 10 Planning for sub-tropical humid zones

The edge of the concrete slab- good thermal linking. A study10 has achieve a surface density of at least on-ground should be insulated in shown that the use of hollowcore 220 kg/m2 are: severe cold climates to prevent heat suspended floors provides additional n Two leaves of 90-mm or greater loss. To maximise heat exchange passive cooling/heating effect, when concrete masonry. to and from the slab, the surface compared to a masonry house with n 140-mm or greater dense-weight receiving sunlight should not be suspended timber floors. hollow concrete blocks with carpeted. A thermally-effective finish Composite floors consisting — 10 mm plasterboard or render; can be achieved by using materials of precast concrete permanent and such as high density concrete or formwork (reinforced or prestressed) — at least one concrete-grouted terracotta tiles, fixed directly to and an insitu concrete topping horizontal bond beam; and the slab using a full-bed mortar- are also effective. The concrete — vertical cores filled with based adhesive. Alternatively, a formwork can immediately be used concrete grout at centres not vinyl floor covering will provide an as a working platform. Minimum or exceeding 1000 mm. intermediate level of effectiveness. zero propping is required. Services n 140-mm or greater concrete wall Slab-on-ground floors with such as under-floor heating/cooling panels and dense-weight hollow under-floor insulation work well systems can be installed prior to concrete blocks with all vertical with under-floor heating, which is placing the insitu concrete topping. cores filled with concrete grout. ideally suited to high thermal mass The soffit of the panel usually has a n 190 mm thick or greater dense- dwellings. Generally, the pipework high quality finish which can simply weight hollow concrete blocks for an under-floor system is located be painted. with at lease one concrete- within the surface screed. Guidance grouted horizontal bond beam; Walls on designing and sizing under-floor and vertical cores filled with The Building Code of Australia heating systems can be found in concrete grout at centres not (BCA)11 provides the basis for Concrete Floor Heating 9. exceeding 1800 mm. building regulations in each Upper floors Australian state and territory. The thermal resistance Concrete suspended floors may Volume 2 is applicable to Class 1 of concrete walls should be provide many of the same benefits detached housing and Class 10a augmented by some form of as slab-on-ground by virtue of minor structures, while Volume 1 insulation, particularly in colder their substantial thermal storage applies to all other buildings. BCA climates, to ensure that the benefits capacity. Many precast concrete 2010 Volume 2 makes provision of the thermal mass are realised. suspended flooring systems are for external walls with high thermal Ideally, the insulation should structurally stronger, have better mass, ie having a surface density be placed on the outside of the fire and acoustic ratings, and can of 220 kg/m2 or more. These are building, and the thermal mass offer speed of construction, when deemed to achieve acceptable retained on the inside. Insulated compared to lightweight alternatives. levels of thermal performance in concrete panels (or 'sandwich The high quality fair-faced finish certain climate zones, due to their panels') offer a solution. They of precast hollowcore units makes ability to store heat (thermal mass) consist of a polystyrene core them an ideal choice. The soffit and slow the heat transfer through 'sandwiched' between two concrete only requires painting, leaving the the building fabric. Examples of panels, and bound together during concrete surface fully exposed for typical wall constructions that casting with non-metallic ties.

Briefing 12 april 2010 Page 7 12 Construction using these panels CCAA OFFICES References

AP r is no more difficult than with standard 1 CCAA website – www.ccaa.com. SYDNEY OFFICE: 2010 solid concrete panels, but it offers au/LCA. Level 6, 504 Pacific Highway St Leonards NSW Australia 2065 significantly better thermal and 2 Environmental Issues: Energy POSTAL ADDRESS: acoustic insulation. Use and Conservation, Locked Bag 2010 Using concrete for internal walls ABS Report 4602.0.55.001, St Leonards NSW 1590 TELEPHONE: (61 2) 9437 9711 can substantially increase the March 2008. FACSIMILE: (61 2) 9437 9470

heat storage capacity of the whole 3 Electricity price rises across BRISBANE OFFICE: building. Thickness of internal walls Australia, www.dme.qld.gov.au. Suite 2, Level 2, 485 Ipswich Road should meet BCA requirements for 4 http://news.theage.com.au/ Annerley QLD 4103 TELEPHONE: (61 7) 3227 5200 sound insulation and fire safety. breaking-news-national/ FACSIMILE: (61 7) 3892 5655 electricity-prices-to-rise-by-up-to- Concrete – the responsible choice MELBOURNE OFFICE: 64-20100318-qgk9.html 2nd Floor, 1 Hobson Street Sustainable development is the 5 Thermal Mass Explained The South Yarra VIC 3141 outcome of giving balanced TELEPHONE: (61 3) 9825 0200 Concrete Centre, 2006. consideration to the three pillars of FACSIMILE: (61 3) 9825 0222 6 Phillips, R O Sunshine and Shade sustainability; social, environment PERTH OFFICE: in Australia Technical Report 45 Ventnor Avenue and economic. No. 92/2, CSIRO, 1992. West Perth WA 6005 n Social – Concrete’s strength, TELEPHONE: (61 8) 9389 4452 7 Passive Solar Design Briefing 09, thermal mass, fire resistance FACSIMILE: (61 8) 9389 4451 Cement Concrete & Aggregates and sound insulation properties ADELAIDE OFFICE: Australia, 2003. PO Box 229 create housing with excellent 8 Climate-responsive House Fullarton SA 5063 living comfort, security, health TELEPHONE: (61 8) 8274 3758 Design with Concrete (T58) and safety leading to an premixed concrete and Cement Concrete & Aggregates improved social infrastructure. EXTRACTIVE INDUSTRIES OFFICE Australia, 2007. PO Box 243 n Environment – Concrete’s thermal Henley Beach SA 5022 9 Concrete Floor Heating mass reduces the whole-of-life TELEPHONE: (61 8) 8353 8151 Briefing 07, Cement Concrete & FACSIMILE: (61 8) 8125 5822 energy use and associated Aggregates Australia, 2002. greenhouse gas emissions from TASMANIAN OFFICE: 10 Thermal Mass for Housing The PO Box 246 a typical house, and results in a Sheffield TAS 7306 Concrete Centre, 2008. lower environmental impact. TELEPHONE: (61 3) 6491 1509 11 Building Code of Australia FACSIMILE: (61 3) 6491 2529 n Economic – Concrete’s excellent Australian Building Codes Board, durability, low maintenance WEBSITE: www.ccaa.com.au 2010. requirements and high energy- EMAIL: [email protected] efficiency reduces the overall Disclaimer: Cement Concrete & Aggregates Australia is a not for profit organisation sponsored cost of both construction and by the cement, concrete and aggregate industries operation phases, and results in in Australia to provide information on the many uses of cement, concrete and aggregates. This better economic outcomes. publication is produced by CCAA for that purpose. Since the information provided is intended for In Australia, there has been general guidance only and in no way replaces the growing awareness of the need to services of professional consultants on particular projects, no legal liability can be accepted by CCAA build energy efficient houses, with for its use.

optimised thermal performance CCAA respects your privacy. Your details have and occupancy comfort. When been collected to provide you with information on our activities, publications and services. From time concrete’s thermal mass is used in to time your details may be made available to third party organisations who comply with the Privacy building design, household energy Act such as affiliated associations, sponsors of consumption and CO emissions events and other reputable organisations whose 2 services we think you may find of interest. If you do can be significantly reduced by not wish to receive information from CCAA or wish reducing or eliminating the need to be taken off the database please write to the Privacy Officer, CCAA, Locked Bag 2010, for heating and cooling systems. St Leonards, NSW, 1590

It makes economic sense for ISSN 1447-199X householders to invest in a thermally comfortable home that will provide cost savings for the rest of its life. Concrete is the responsible choice for energy-efficient homes and sustainable development.