Human Settlements Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Professor Peter W. Newton, CSIRO Building, Construction and Engineering, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06747 7
Urban stocks and processes (continued)
Buildings are high consumers of energy - both embodied and operating - and therefore have a significant impact on our environment.
Embodied energy is the energy consumed by all of the processes associated with the production of a building, from the acquisition of natural resources to product delivery, including mining, manufacturing of materials and equipment, transport and administrative functions. The study of embodied energy gives us an understanding of how much and where energy is used in the construction of buildings, and the financial benefits of recycling.
Carbon dioxide (CO2) emissions are highly correlated with the energy consumed in manufacturing building materials. On average, 0.098 tonnes of CO2 are produced per gigajoule of embodied energy of materials used in construction. Concrete and aluminium are higher than average and glass is lower. The energy embodied in the existing building stock in Australia is equivalent to approximately 10 years of the total energy consumption for the entire nation. Choice of materials and design principles have a significant impact on the energy required to construct a building. However, this energy content of materials has been little considered in design until recently, despite such impacts being recognised for over 20 years.
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 (Figure 33). But using these values alone to determine preferred materials is inappropriate because of the differing lifetimes of materials, differing quantities required to perform the same task, and different design requirements.
Figure 33: Embodied energy of selected building materials and totals in a typical dwelling. [HS Indicator 6.7]
Source: Produced by CSIRO using data from Tucker et al. (1999) and Treloar (2000)
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 (Figure 33). Thus, the greatest amount of embodied energy in a building is often in concrete and steel, particularly for housing on concrete slabs and reinforced concrete buildings. The use of recycled of steel would lower its contribution to embodied energy.
In choosing between alternative building materials or products on the basis of embodied energy, not only the initial materials should be considered but also the materials consumed over the life of the building during maintenance, repair and replacement. As buildings are becoming more energy efficient in their operation, the embodied energy is approaching half the lifetime energy consumption in some circumstances.
The reuse of building materials commonly saves about 95% of embodied energy which would otherwise be wasted. Some materials such as bricks and tiles suffer damage losses of up to 30% in reuse. The energy saved by recycling of materials for reprocessing varies considerably, with savings of up to 95% for aluminium but only 20% for glass. Some reprocessing may use more energy, particularly if long transport distances are involved.
The minimal changes in dwelling material supply and selection over the last 10 years means that the environmental impacts from the choice of material have changed little. The exception is the growing percentage of dwellings that are insulated. Since surveys began in November 1980, the proportion of dwellings with some insulation has risen from about 42% to 53% in March 1999 (ABS 1981, 1984, 1987, 1999a).
Although there has not been an enormous change in types of construction, there has been an increase in floor area, which naturally translates to more building materials being used per dwelling. This has a direct influence on the embodied energy of a typical dwelling. The average embodied energy of a newly constructed dwelling is around 5 GJ/m2. Average floor area has increased by 20% since 1991, so embodied energy has also increased by 20%. In 1991 the average floor area was 185.4 m2, which translates to an embodied energy of 927 GJ. By 1999 the average floor area had increased to 223 m2, which means the embodied energy had increased to 1118 GJ.
There are two main legislative methods available in Australia to ensure energy efficient dwellings. The first is the Building Code of Australia (BCA) with which all buildings must comply. States and territories are able to add additional requirements to the BCA to cover areas such as energy efficiency. At this stage only Victoria and the ACT have utilised this method of legislation (Table 22).
|Victoria||To have roof/ceiling insulation of at least R2.2 and external wall insulation providing a total element R value of at least R1.3 or external wall insulation of at least R1.7 (assuming floor insulation of R0.7). Alternatively, achieve a House Energy Rating of at least 3 stars||1991||All new dwellings|
|ACT||A building, including carpets and internal fittings, must achieve an annual energy consumption rate for heating and cooling not greater than 255 MJ/m based on the ACT climate zone. This is equal to an ACT House Energy Rating of 4 stars||1996||All new dwellings and additions|
The second is through the planning codes system. In most states and territories this is administered by local government. New South Wales has adopted this approach with the establishment of the Energy Smart Homes policy. This is a voluntary policy which local councils can adopt and implement through their building permit system. Participating councils require that new homes, major alterations and additions in their area achieve an energy-efficiency rating of at least 3.5 stars. Since the program's implementation in 1998, 51 local governments have joined, covering around 8% of the population in New South Wales. However, few actually enforce the energy rating at present.
In many states and territories it is difficult to determine how many new homes achieve 3 to 3.5 stars. In some instances, standard building practice along with the climatic conditions alone will achieve 3 stars. However, this cannot be assumed, and only one formal study has been undertaken to determine the likely star ratings for new housing in each state and territory.
In Victoria, the average star rating for a sample of new Melbourne houses in 1999 was 2.3 - well below the intention of the BCA requirements, which permitted specified insulation levels as an alternative to achieving a 3-star rating. The Australian Greenhouse Office (AGO 2000) states:
It seems that the Deemed-to-Satisfy insulation provisions have produced an average thermal efficiency result somewhat below the performance target of 3 stars...Despite the introduction of mandatory minimum insulation requirements, a significant number of poorly performing houses are produced each year. For detached housing almost half of the sample performs at or below the 2 star level...
The operational energy savings that can be achieved through the improvement in a star rating of a dwelling depend on the climate. Most energy savings are gained through the reduced operation of heating or cooling appliances. This not only translates into savings in energy, but also a saving in operating costs in comparison to a 1-star dwelling (see Table 23).
Source: Sustainable Energy Authority, Victoria.
Energy reductions also have a direct effect on greenhouse gas emissions, especially CO2. Heating and cooling energy, on average, account for about 15% of the total greenhouse emissions from (Harrington et al, 1999) a dwelling (much higher in more extreme climates), with the main consumers being hot water systems and electrical appliances. Current building trends do not seem to be restricting heating and cooling greenhouse emissions to this very modest increase. Indeed, a recent report on greenhouse emissions for the residential building sector suggests that by 2010 emissions will have increased by 140% from 1990 levels and will continue to increase. Even with an aggressive campaign of encouraging energy-efficient building and retrofitting existing stock, it is predicted that the increase by 2010 will still be around 112% (AGO 2000). It is important that builders are aware of these impacts, and of the fact that reductions in greenhouse emissions from residential buildings can only be achieved through a committed effort by both builders and owners. Improving a dwelling's rating from 1 to 5 stars reduces annual CO2 emissions by approximately 1.5 tonnes in Brisbane, 3 tonnes in Melbourne, and up to 4 tonnes in Sydney. This compares with an average Australian household's annual emissions from non-transport energy use of 8.2 tonnes in 1995 (Wilkenfeld and Associates 1998).
In the energy sector it is a time of uncertainty and contradiction, but also a time for choice. At present, our supply and consumption of energy is spiralling further into unsustainability. Yet the technologies and systems that can underpin progress towards sustainability are available, and are becoming cheaper, more reliable and more effective. Our ability to understand the implications of decisions and actions by using tools such as life-cycle analysis is also improving rapidly.
If Australia's energy trends continue to follow the 'business as usual' scenario, the implications are as follows:
- Ongoing growth in emissions from energy supply and consumption will place Australia's compliance with the Kyoto targets, and likely further requirements for reductions in greenhouse gas emissions, under threat. This will necessitate aggressive additional strategies, such as reforestation and rapid development of techniques for long-term storage of CO2, to compensate for ongoing growth in emissions from energy supply and use.
- Maintenance of, or improvements in, urban air quality will be achieved only by ongoing tightening of emissions controls, particularly on cars and trucks. Outcomes will depend on the strength of measures and the turnover of the vehicle population.
- Urban traffic congestion will continue to increase.
- Substantial capital investment in additional energy supply capacity will be required, such as oil shale and oil from coal, as well as some renewables.
- Exports of fossil fuels and energy-intensive commodities will continue to be a significant component of the Australian economy.
- Low-income and rural households may, without government intervention, experience higher energy costs and transport costs as a proportion of total income.
- While energy costs for industries may remain low, their total energy costs may rise relative to international competitors because their energy efficiency will improve more slowly.
- The full cost-effective potential of energy-efficiency improvement will not be realised.
- The economic risk of pursuing a fossil fuel-based path will increase, as fossil fuel exports may be adversely affected by other countries' greenhouse response strategies.
- Our dependence on imported oil and associated balance of payment impacts is likely to increase over the next few decades.
If we pursue a sustainable energy path, the implications are as follows:
- There is a risk of slightly slower economic growth (of the order of 0.6% per annum lower) if some economic modelling (which includes limited potential for cost-effective energy efficiency improvement and relatively expensive renewable energy sources) is correct (Brown et al. 1999).
- Strong government intervention will be required, as many institutional factors work against the rapid adoption of energy-efficiency improvement and renewable energy, and there is limited infrastructure to implement rapid growth in energy efficiency and renewable energy.
- We will need to develop strong exports in services, manufactured goods and sustainable energy solutions to maintain export revenues.
- A shift towards energy efficiency and distributed energy supply will make our society more resilient to problems and create employment in a wider range of regional areas.