The evaluation of the 5-star energy efficiency standard for residential buildings

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Ambrose, Michael ORCID ID icon; James, Melissa ORCID ID icon; Law, Andrew; Osman, Peter; White, Stephen



232 p

BACKGROUND In 2006, the Building Code of Australia (BCA) set a new residential building energy efficiency standard of 5 stars, as rated by software tools accredited under the Nationwide House Energy Rating Scheme (NatHERS). To reach the 5-star energy efficiency standard, architects and builders could choose from a large variety of options, such as increasing insulation in ceilings, walls and floors; using double glazing; and redesigning house layout and orientation. The Regulation Impact Statement (RIS) on the 5-star standard analysed its likely impact on the energy efficiency of new houses relative to the previous standard. The RIS estimated that the 5-star standard would reduce heating and cooling energy costs, as well as greenhouse gas emissions. In 2012, to assess whether the new standard was achieving its goals, the Australian Government asked CSIRO to: i) find out whether the 5-star standards have actually reduced heating and cooling energy use of houses compared with those built to the earlier 3.5 to 4-star standard; and ii) determine the actual benefits and costs of meeting the 5-star standard To undertake this task, CSIRO studied 414 houses in the principal centres of population of three BCA climate zones over a winter and summer period. KEY FINDINGS This report details CSIRO’s response to the above questions. In this report, 5-star (or above) houses are referred to as higher-rated houses, while houses less than 5-stars were referred to as lower-rated houses. The findings should be regarded as preliminary, because research work and monitoring is ongoing and relevant only to the houses that were included in this study (i.e. detached houses built in the last ten years in Brisbane, Adelaide and Melbourne). Several factors have made it difficult to draw robust conclusions about the differences in energy use between lower-rated and higher-rated houses that could be applied to other such houses across Australia. Some of the factors causing this uncertainty are briefly described below. -The uneven distribution of houses across star rating values in the data set means that the sample size restricts the conclusions that we can make. -The small sample size causes uncertainty about how representative the data set is of Australia's households, particularly in relation to household type, occupancy patterns and user behaviour. -The above-average temperatures during the summer period make it likely that air-conditioning appliances were operating at full capacity, regardless of star rating, making it difficult to detect differences between lower and higher-rated houses. -The higher-rated houses were generally constructed more recently than the lower-rated houses, and further investigation is needed to check whether this caused any inherent bias. For example, the newer, higher-rated houses were more likely to contain younger children, have someone home all day, and identify themselves as high energy users. -The expected energy ratings of the houses in our sample have not increased in line with the changes in building regulation. The reasons for this, as well as the quality of build compliance issues raised by the study, needs to be further examined. Increased monitoring of houses across Australia will help to provide a clearer picture of the impact of increasing star ratings on household energy consumption. Data collected through this analysis should also be compared with alternative data sources to provide a more robust understanding of house performance. Essentially, our main findings are as follows. The 5-star standard significantly reduced the energy needed to maintain house temperatures in winter in the houses we studied. As well as saving energy, higher-rated houses were on average held at a temperature around 1 °C higher than lower-rated houses during winter. It is not clear if this was because the occupants had set the temperature higher, or whether it was an innate property of the control system or a result...


Highett, Vic.

energy efficiency; NatHERS; residential buildings; energy monitoring

Building Science and Techniques

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© Commonwealth of Australia (Department of Industry) 2013. This work is licensed under the Creative Commons Attribution 3.0 Australia Licence. To view a copy of this licence, visit


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Ambrose, Michael; James, Melissa; Law, Andrew; Osman, Peter; White, Stephen. The evaluation of the 5-star energy efficiency standard for residential buildings. Highett, Vic.: CSIRO; 2013.

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