CSIRO Confirms 5 Star Rated Houses Cost Less To Run And Less To Build

Back in 2006 the Building Code of Australia (BCA) set a new residential building energy efficiency standard of 5 stars, under the Nationwide House Energy Rating Scheme – or NatHERS. A CSIRO team recently evaluated the energy results so far.

House energy rating through the Nationwide House Energy Rating Scheme (NatHERS) uses computer simulations to assess the potential thermal comfort of Australian homes on a scale of zero to 10 stars. Put simply, according to NAtHERS, “the more stars, the less likely the occupants need cooling or heating to stay comfortable”.

A dwelling can be rated before or after it is built. The rating depends on:

  • the layout of the home
  • the construction of its roof, walls, windows and floor
  • the orientation of windows and shading to the sun's path and local breezes
  • how well these suit the local climate.

In 2012, to assess whether the 5 star standard achieved its goals, the Australian Government asked CSIRO to:

  • 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
  • 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. 

The study, The Evaluation of the 5-Star Energy Efficiency Standard for Residential Buildings has recently been released and reaches some clear conclusions:

The higher star standard significantly reduced the energy needed to keep houses warm in winter.

  • In higher-rated houses average winter energy use compared to lower-rated houses was 50 per cent less in Melbourne, 19 per cent less in Adelaide and negligible in Brisbane. These houses were also on average 1 degree warmer than lower-rated houses with energy ratings of less than 5.
  • It is cheaper to build a 5 Star or higher-rated house than a lower-rated house. The average savings for the elements of a building related to achieving the higher star rating were $7,500 in Brisbane, $5,500 in Adelaide and $5,000 in Melbourne. This result was mainly due to increases in insulation and a more rectangular floor plan.
  • Overall greenhouse gas emissions for higher rated houses in all cities were found to be 7% less over the year. This is despite greater summer cooling energy use in these houses in Melbourne and Brisbane and increased greenhouse gas emissions in all higher-rated houses during this season. The report indicates that the increased greenhouse gas emissions during this time could be because the residents of these houses tend to have children and greater daytime occupancy than the lower-rated houses. (Source: Sanctuary)
  • From a sample of 20 standard modern houses in Melbourne, selected for blower door air pressure testing to determine the ‘leakiness’ of a house, the 20 homes needed to be re-heated or re-cooled on average every hour, compared to global best practice of over three hours. So, despite improving our insulation and glazing levels in recent years, Australian homes are still three times worse in retaining conditioned air than equivalent homes in Europe and North America.

The CSIRO also concluded that the research has shown that a great deal of further measurement and analysis is required to enable effective decisions about the future of house cooling energy efficiency in Australia.'

CSR also agrees that further research and education is required to better communicate the benefits of efficient operation of buildings; and a greater understanding of heating and cooling appliance selection and operation is encouraged in the general community to ensure real savings can be achieved in energy use.

While Australia has seen improvements in performance levels of insulation and glazing, a number of areas still remain to be addressed to ensure substantial overall energy savings are achieved in new buildings, including: air tightness, shading of windows, installation practices of materials, and further training of trades in efficient building performance.

To read the full report: The Evaluation of the 5-Star Energy Efficiency Standard for Residential Buildings

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