Residential buildings are responsible for 24 per cent of electricity use and 12 per cent of carbon emissions in Australia. Heating and cooling accounts for a major portion of residential energy consumption and emissions. However, energy efficiency is often forgotten by homeowners and buyers amongst the many other factors such as cost, design, location, and convenience.
Improving thermal comfort is fundamental to reduce carbon emissions from the housing sector. With the urgency of climate change and risks of more frequent extreme weather events, the need to increase the thermal efficiency of homes is critical. Doing so would also help improve health, liveability and affordability for households.
Our recently released report identified priority research areas to accelerate the adoption of home thermal efficiency in Australia. Building fabric improvement is the top priority item. Specifically, we found that encouraging the adoption of high-performance windows and managing water vapour and ventilation are crucial.
Increasing the accuracy of rating tools such as NatHERS is fundamental in addressing airtightness and condensation during the construction and operation stages using more realistic air tightness levels. We found the gap between design and performance was often policy and regulatory in nature including a lack of accountability post-construction, with the absence of as-built verification being a key barrier.
The thermal performance of a large proportion of Australia’s existing ten million homes is poor. Housing energy assessments that provide independently verified, reliable, clear, and accurate information are needed for homeowners to make retrofit decisions. However, designing an effective and affordable assessment tool is challenging, although examples exist in places like Europe which we could draw upon.
Households may not know what is required, what the benefits are, or how to prioritise and specify improvements. To assist homeowners to progress and complete a retrofitting journey, a one-stop shop offering all the services required for a complete home energy upgrade is needed. This would manage home energy upgrades from start to finish and offer a smooth customer journey and better outcomes.
Benefits of thermal efficiency and how to measure them
A pseudo database of existing building stock covering all the states and territories, was developed based on 208,204 recent real dwelling designs with NatHERS ratings but with envelope insulation removed. This is to simulate pre 2006 building practices and then determine energy efficiency and overheating risks for different building improvements under the current climate and projected future 2030 and 2050 climates.
Three levels of building improvements were investigated in this study: rehabilitation (ceiling insulation, door seals, windows shades and curtains), refurbishment (ceiling insulation, door seals, windows shades, curtains and addition of glass layer on windows) and renovations (deep retrofitting).
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Figure 1 shows the average number of overheating hours for Class 1 dwellings in each state and splits the overheating hours into day and night. Tasmania has the coldest climate of any part of Australia and consequently, the average number of overheating hours is very small for all the improvement scenarios that were modelled. The average of 72 overheating hours for the base design is reduced to 19 hours under the full renovation improvement.
By contrast, South Australia’s average of 1884 overheating hours for the base design is reduced by 55 per cent to 839 hours for the renovation improvement. The Northern Territory’s very high average overheating hours mainly come from overnight overheating in bedrooms and Queensland also sees more night-time overheating. In most other jurisdictions it is daytime overheating that makes up the majority. Reductions that are achieved through improvements are mainly through reductions in daytime overheating whereas night overheating hours remains similar across the improvements.
Heating and cooling energy costs and emissions were also estimated (Figure 2). Improving an extra 5 per cent of building stock by simple refurbishment would save $185 million and cut 1.57 Mt annual CO2 emission whereas deep retrofitting would save $439 million and cut 3.6 Mt CO2 per year. Improving an extra 40 per cent of building stock by simple refurbishment would save $1.48 billion and cut 12.58 Mt annual CO2 emission whereas deep retrofitting would save $3.58 billion and cut 28.78 Mt CO2 per year.
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The report identified the significant opportunity for improving the thermal performance of our existing housing in Australia. This would result in a substantial reduction in energy consumption and associated emissions from the housing stock and should therefore be a key pillar in government policy as part of any pathway towards a low carbon future.
Improvements to the thermal performance of existing housing would also reduce energy bills for households and make them more affordable as well as improving health and wellbeing outcomes. There would also be wider benefits such as benefits for the energy grid.
Michael Ambrose and Dong Chen from the CSIRO and Trivess Moore, Mary Myla Andamon and Alan Pears from the Sustainable Building Innovation Lab at RMIT University also contributed to this report, which was based on research funded by RACE for 2030 CRC www.racefor2030.com.au.
