Around Australia, much effort has been afforded to building homes which stay warm in winter and minimise energy costs. Less attention has been given to heat resistance in summer.
Indeed, there is growing evidence that many newly built homes fail to provide greater relief from extreme summer heat than that achieved in older houses.
In research published last year, University of South Australia researcher Dr Gertrud Hatvani-Kovacs compared the performance of single-storey brick veneer homes constructed to different levels under the NatHERS energy rating system using both traditional and modern building methods across Adelaide and Sydney during heatwaves. She found that a newer brick-veneer home with a six-star rating used the same amount of energy to cool the interior compared with an older, double brick home of just 2.6 stars.
Earlier research published in 2015 by RMIT researchers Nicola Willand and Professor Alan Pears along with City University of Hong Kong Professor Ian Ridley looked at 107 homes in Melbourne. It found that at a heat wave threshold of 25 degrees Celsius, higher-rated six-star homes were on average 0.89 degrees warmer compared to those with ratings of four or five stars.
Part of this relates to NatHERS itself. Since 2011, all new buildings have been required under the National Construction Code to achieve six-star NatHERS ratings. In NSW, a separate rating system known as BASIX applies. These ratings, however, are calculated according to a home’s expected energy consumption over the whole year. Energy efficiency, Hatvani-Kovacs points out, is different from heat resistance. Moreover, a focus on winter heating in southern states has meant houses have been able to achieve high overall energy scores (and thus required NatHERS ratings) without adopting measures to cool homes in extreme heat.
Moreover, Hatvani-Kovacs and Pears say that without cooling measures, the greater insulation and air-tightness which keeps new homes warm during winter traps in heat and makes dwellings hotter during summer.
Hatvani-Kovacs says other factors also contribute to newer homes being less heat-resistant. As lot sizes condense and houses are built closer together, opportunities to achieve ventilation without compromising privacy are becoming more restricted. Despite absorbing heat, black roofs remain fashionable. Wide eaves – important for shading – have become less common.
The upshot is that homes are reliant on air-conditioning. This, Hatvani-Kovacs says, has consequences. First, both by forcing residents to run their systems and adding to peak energy demand (and thus prices) on hot days, it drives up the cost of cooling homes. By dumping waste heat from air-conditioners into streets, it raises local street temperatures. Air-conditioning also changes behaviour as a reverse adaption effect sees building occupants become acclimatised to cooler environments and thus demand yet lower temperatures (and more air-conditioning). Finally, homes which rely on air-conditioning and thus electricity raise health concerns when the grid fails.
That last factor is critical. In the Melbourne heatwave spanning January 27 to 31 in 2009, 374 deaths were recorded over and above the normal fatality rate, whilst emergency cases and emergency department presentations rose by 25 per cent and 12 per cent respectively. Around a third of all deaths which occur during heatwaves happen indoors, Hatvani-Kovacs says.
She says Australia needs to change its approach.
“We don’t tackle this issue with anything else apart from air-conditioning,” Hatvani-Kovacs said. “We need to tackle this issue from a different perspective. This involves a more heat sensitive design not just an energy efficient design.”
Pears says heat resistance during summer has been neglected in favour of winter warmth.
“Yes, Australia has a significant and increasing problem with housing in summer,” he said in a written response to questions.
“Climate change and building design focuses on improving winter performance at the expense of summer performance are driving this.”
Going forward, Hatvani-Kovacs supports a proposal for change which has been included in the Public Comment Draft for the NCC 2019 under which separate thermal energy standards will apply for heating and cooling. Provided these are reviewed to increase stringency over time, she says this will help drive change and direct focus toward heat resistance as well as winter thermal comfort.
On site, she stresses that each project should be considered in its own context. Relevant factors include orientation, shading, use of insulation, whether to have an elevated slab (since ground temperature varies less than air temperature, ground slabs will often perform better in heat waves), installation of outdoor blinds and planting of deciduous trees.
Pears supports the NCC change but says regulation alone will not be sufficient. He says Australia needs housing which provides comfort and avoids air-conditioning reliance. Important features include ‘refuge rooms’, small and efficient battery/PV powered fans and air-conditioners and insulated and shaded spaces which provide a comfortable core space in extreme heat. He says heat should be managed through glazing (including shading), internal heat generation management, ventilation, a thermally efficient building envelope, vegetation and light coloured permeable paving, efficient cooling systems, thermal or electricity storage, suitable clothing for hot days and greater education for building operators and home occupants.
On policy, he says the Code change should be supported by restrictions in allowable peak heat flow through the building envelope; incentives for shading and high-performance glazing; insulated internal blinds and light coloured roofs; education for operators and occupants; packages of shading, cooling equipment and light coloured paint and measures for vulnerable households.
Focus should extend to retrofitting existing homes, he said.
Australia is building warmer homes for winter.
We must also build cooler ones for extreme summer heat.