|Page tools: Print Page|
Construction and the environment
The materials selected for building also influence the environmental impact of construction. The main factors determining the level of impact are the source of materials and the way they are processed. Similar materials can have greatly different environmental impacts depending on these factors. Important factors influencing selection of residential construction materials are their durability compared to intended life span, lifecycle energy consumption, source and environmental impact of all component materials and processes, recycling potential, and distances required for transportation of components.
The harvesting of many materials used in building a home can cause adverse impacts on biodiversity, including extinction of species, destruction of natural systems and habitat, degradation of ecosystems and fragmentation of habitat and populations. For example, harvesting of timber for construction from native forests can reduce the habitat of native species (AGO 2002c).
These impacts are rarely apparent at the point of use, so it is difficult for builders to take them into account when selecting construction materials. More information is becoming available to help builders in selecting environmentally preferred materials. Choosing an appropriate combination of materials to build houses, taking into account the climate and location, will increase thermal comfort, lower costs and reduce the overall environmental impact (AGO 2002a).
As well as using more materials and, in some cases, more land, increased construction activity can lead to increased production of waste, use of energy and greenhouse gases emissions.
Australians generate on average about one tonne of solid waste per person per year, which goes to landfill (AGO 2002d). Construction and demolition of buildings contributes 30-40% of this waste (table S20.2). This equates to about eight million tonnes nationwide, or 430 kg/year per capita (Newton et al. 2001). The impacts of landfill disposal include use of land that could be used for other purposes, release of methane from the decomposition of organic wastes, and greenhouse gas emissions through the transportation of wastes to landfills, which are mostly on the fringes of cities (Newton et al. 2001). Other environmental implications of disposing of construction waste can include depletion of natural resources and wastage of energy required to produce materials.
The main type of waste is soil rubble, followed by concrete-based masonry and clay-based waste such as bricks and tiles (graph S20.3). Some types have greater impact than others. For example, gypsum plasterboard disposed of in landfill produces poisonous hydrogen sulfide (AGO 2002d).
The amount of waste is being reduced by construction companies using the following established hierarchy for waste minimisation: reducing consumption of resources where possible; reusing existing buildings and materials; and recycling resources that are left over or have reached the end of their useful life. Effective waste minimisation strategies are being agreed to and implemented by all parties involved in building at the design, construction and operation stages. Decisions on what to build, whether to demolish, what materials to use and how they might be recycled are now made from the earliest stages of design and incorporate waste minimisation strategies (AGO 2002d).
The article The WasteWise Construction Program discusses in detail the coordinated responses to achieve waste reductions.
Energy consumption impacts on the environment through its depletion of non-renewable resources and emission of greenhouse gases. The impact depends to a large extent on the energy source. This is discussed further in the section Energy and the environment in Energy.
Energy consumption by the construction industry in residential, commercial and other developments is relatively low. In 1997-98, the industry consumed 73 PJ of energy, only 0.5% of total energy use. Primary energy (raw materials) used by the construction industry consisted of 2 PJ of natural gas and 2 PJ of liquefied petroleum gas. Secondary energy products (those that have been enhanced or changed before consumption) consisted of 7 PJ of automotive petrol, and 62 PJ of gas oil or fuel oil (ABS 2001c).
Despite the low direct energy use by the construction industry, once buildings have been constructed they become high consumers of energy. An understanding of energy consumption and the associated greenhouse gas emissions needs to take into account both embodied energy and operating energy.
Embodied energy is the energy consumed by processes associated with the production of a building, from the acquisition of natural resources to final consumption including mining, manufacturing, transport and other functions.
The energy embodied in the existing building stock in Australia is equivalent to about 10 years of the total energy consumption for the entire nation. The embodied energy per unit mass of materials used in building varies enormously, from about two gigajoules per tonne for concrete to hundreds of gigajoules per tonne for aluminium. However, other factors also affect environmental impact, such as differing lifetimes of materials, differing quantities required to perform the same task and different design requirements. Materials such as concrete and timber have the lowest embodied energy intensities, but are consumed in very large quantities, whereas materials with high energy content such as stainless steel are used in much smaller amounts (Newton et al. 2001).
The principal material of the outside walls for dwellings in Australia is brick veneer (41% of dwellings) (ABS 1999). In brick veneer construction, the bricks have no structural role, but high embodied energy. Lightweight materials such as fibre cement have lower embodied energy but similar structure and thermal performance (AGO 2002a).
Embodied energy is becoming of greater significance as a proportion of whole-of-life energy consumption, particularly in the commercial building sector, due to several trends - more energy intensive materials such as aluminium and stainless steel are being used in buildings; these are often bigger and therefore require greater quantities of materials; buildings are being refurbished more frequently, requiring more materials; more machine intensive techniques that require energy derived from fossil fuel sources are used in construction; and building materials are transported greater distances, so that transport energy is likely to be greater (AGO 1999a).
Recycling building materials can reduce embodied energy substantially. For example, aluminium is 100% recyclable. Recycling aluminium reduces embodied energy by 95%, while recycling steel reduces embodied energy by 72% (AGO 2002d).
Operating energy is the energy consumed in maintaining and using a building throughout its life span. Levels of operating energy can be influenced by the design and materials initially used in construction.
In residential buildings, space heating and cooling accounted for 39%, or approximately 125 PJ, of total residential operational energy consumption in 1998 (graph S20.4). The main energy sources used in the residential sector are electricity, natural gas and wood. The vast majority of natural gas and wood consumption in Australia is for space heating. Firewood is often collected from areas where the fallen timber provides crucial habitat and food for native animals, and this practice can pose a threat to forest biodiversity (ANZECC 2001).
In commercial buildings, heating is the largest single end use of energy at 33% of total energy use in 1990 (graph S20.5). By type of energy, electricity accounted for 65% of energy used, followed by natural gas at 25% (AGO 1999a).
Technologies for reducing operating energy are being developed and implemented. In the foreseeable future it is likely that buildings will generate some of their own operating energy, by devices such as photovoltaics, which may be integrated within the building fabric.
Greenhouse gas emissions
It is becoming widely recognised that human activities such as energy consumption are influencing global climate change through emissions of greenhouse gases such as carbon dioxide. Environment provides information on greenhouse gases.
Although the construction industry itself induces a fairly small amount of direct greenhouse gas emissions, buildings and other forms of construction contain high levels of embodied energy due to their use of building materials which are energy-intensive to produce, and therefore induce a large amount of greenhouse gases indirectly.
The direct greenhouse gas emissions from the construction industry were 4,958 Gg CO2-e in 1997-98, compared with the total emissions of all industries and direct emissions by households 339,597 Gg CO2-e. Greenhouse gas emissions can also be calculated indirectly. This method includes emissions from the extraction, harvesting, processing and transportation of materials used in the construction industry, as well as those produced by the industry itself. Construction produced 7.1% (21,397 Gg CO2-e) of total indirect greenhouse gas emissions in 1994-95. This is the third highest overall level of energy-related domestic emissions after electricity and direct consumption by households (graph S20.6).
The average household's energy use is responsible annually for about eight tonnes of carbon dioxide, the main greenhouse gas. Space heating and cooling accounted for nearly 15% of residential sector greenhouse gas emissions in 1998 (graph S20.7). This is a lower share of greenhouse gas emissions than energy use (39%) because a large share of the energy used for heating and cooling is less greenhouse gas intensive (involving use of natural gas and wood rather than electricity).
In commercial buildings, space cooling, ventilation and lighting were found in 1990 to be the three most significant causes of emissions, together accounting for 71% of the total (graph S20.8). The actual proportion applicable to a specific building type may vary substantially from this commercial sector average. A study assessing greenhouse gas emissions by commercial building type found offices to be the most significant, responsible for an estimated 27% of total sector emissions in that year. Hospitals formed the next largest group at 13% (AGO 1999a).
Greenhouse gas emissions related to embodied energy were found to be less significant than those related to operating energy. In a study of four buildings, embodied energy emissions were found to be approximately 8-10% of greenhouse emissions by buildings, assuming a 40-year life span. This proportion would vary substantially for different building types; for those using less operating energy (e.g. warehouses, non-air conditioned offices) it would be much higher.
Many factors can contribute to reducing energy consumption and greenhouse gas emissions. Dwelling design can significantly affect the amount of sunlight entering a home. By siting the rooms that are principally used by the household (e.g. living areas and bedrooms) so that they face north, sunlight can be employed to heat the dwelling in winter. Insulation has a large impact on the heating and cooling requirements for buildings by creating a thermal barrier which reduces the rate of transfer of heat from and into a building. The use of insulation can reduce the amount of energy used to heat or cool a building.
Residential buildings in Australia are generally poorly insulated - 38% of houses have neither wall or ceiling insulation. Only one-fifth of all residential buildings have both wall and ceiling insulation and a further 42% have only ceiling insulation. In 1999, just over half of Australian households reported that their dwellings had some form of insulation. Achieving a more comfortable temperature was the main reason for insulation having been installed (87% of households), and cost was the main factor discouraging people from installing insulation (ABS 1999).
Improving the insulating qualities of new residential buildings goes a significant way towards meeting greenhouse gas emission reduction targets. Residential buildings potentially have a very long life - of the order of 50-100 years - and so any measure implemented will continue to have an impact on energy and greenhouse gas emissions for decades to come (AGO 1999b).
Energy efficiency measures in the Building Code of Australia (BCA)
The BCA is one of the main legislative methods available in Australia to ensure energy efficient buildings. The BCA sets minimum standards with which all buildings must comply. Individual builders may choose to use better performing systems. In 2000, the Commonwealth Government and the state and territory governments reached agreement to develop suitable national energy efficiency provisions for domestic and commercial buildings. The objective of the energy efficiency measures is to reduce greenhouse gas emissions by efficiently using energy. The proposed measures for buildings are intended to achieve significant improvement and eliminate worst practice, thereby reducing greenhouse gas emissions, while avoiding excessive technical and commercial risks and unreasonable costs. Performance requirements relate to building fabrics with an appropriate level of thermal performance, and to building services that use energy efficiently. The energy efficiency measures in the BCA Housing Provisions are expected to come into effect on 1 January 2003 and the commercial energy efficiency measures at a later stage (ABCA 2002).
ABCA (Australian Building Codes Board) 2002, pers. comm. from John Kennedy, Manager, Energy Efficiency.
ABS (Australian Bureau of Statistics) 1999, Environmental Issues: People's Views and Practices, cat. no. 4602.0, ABS, Canberra.
ABS 2001a, Building Approvals, Australia, cat. no. 8731.0, Article 'Average floor areas of new dwellings', ABS, Canberra.
ABS 2001b, Building Approvals, Australia, cat. no. 8731.0, Article 'Largest and fastest growing areas in Australia', ABS, Canberra.
ABS 2001c, Energy and Greenhouse Gas Emissions Account, Australia, 1992-93 to 1997-98, cat. no. 4604.0, ABS, Canberra.
AGO (Australian Greenhouse Office) 1999a, Australian Commercial Building Sector Greenhouse Gas Emissions 1990-2010, Executive Summary Report 1999, Commonwealth of Australia.
AGO 1999b, Australian Residential Building Sector Greenhouse Gas Emissions 1990-2010, Executive Summary Report 1999, Commonwealth of Australia.
AGO 2002a, Construction systems, Design for Lifestyle and the Future fact sheet 3.4, at http://www.yourhome.gov.au.
AGO 2002b, Energy use, Design for Lifestyle and the Future fact sheet 4.0, at http://www.yourhome.gov.au.
AGO 2002c, Materials use, Design for Lifestyle and the Future fact sheet 3.0, at http://www.yourhome.gov.au.
AGO 2002d, Waste minimisation, Design for Lifestyle and the Future fact sheet 3.2, at http://www.yourhome.gov.au.
ANZECC (Australian and New Zealand Environment and Conservation Council) 2001, A National Approach to Firewood Collection and Use in Australia.
Newton PW, Baum S, Bhatia K, Brown SK, Cameron AS, Foran B, Grant T, Mak SL, Memmott PC, Mitchell VG, Neate KL, Pears A, Smith N, Stimson RJ, Tucker SN & Yencken D 2001, 'Human Settlements', in Australia State of the Environment Report 2001 (Theme Report), CSIRO Publishing on behalf of the Department of the Environment and Heritage, Canberra.
These documents will be presented in a new window.