Design for a changing climate: Heatwaves

verandah design for heatwaves

Heatwaves are already becoming more frequent, and are likely to increase exponentially as the climate warms. Dick Clarke and Chris Reardon look at how we need to rethink the way we are designing our homes. 

Climate change is with us and no achievable amount of mitigation is going to reverse its effects sufficiently to prevent our need to adapt. Australian houses today are largely designed or modified based on historic climate data, even though we (or someone else) will be living in them for at least 50 years. Quite simply, this approach is inadequate in a rapidly changing climate. While we will no doubt survive the two to three degrees of warming already locked in, we urgently need to re-think our approach to housing to cope with the extremes.

Hotter for longer

Heatwaves of increasing frequency, intensity and duration are occurring in the southern half of the nation and have already killed many hundreds of people. CSIRO and the Bureau of Meteorology predict that these will increase exponentially. We will not be able to cool or air-condition our way through these crises.

Heatwaves are regional events. When we all cool our homes at the same time, we cause electricity demand to peak and, on top of increasing electricity costs, grid failure becomes increasingly likely during peak demand periods. Homes without an alternative coping strategy will become uninhabitable at best. While those of limited means will likely be most severely affected due to cooling unaffordability and poor home design, comfort moves beyond the reach of everyone when the grid is down.

Australian cities likely to experience increasingly severe heatwaves include Melbourne, Adelaide, Perth, Launceston and Hobart as well as most south-eastern regional areas. These climates traditionally require significant amounts of heating in winter. Our standard design response to-date has been to apply passive design principles, relying on significant amounts of thermal mass.

This approach allows dense materials to store daytime warmth from the sun and release it into living spaces at night to offset the coolest temperatures in winter, and night purging during summer to take advantage of cooler outdoor temperatures.

As the climate warms and winters become shorter, homes in these areas will require less winter heating and more summer cooling. In many of these climates, night purging via cross ventilation and convection (internal hot air rising and exiting that in turn draws in cooler night air at floor level) would become gradually less effective. During heatwaves, temperatures can remain well above comfort levels all night—thus, eliminating any passive cooling opportunities. Under these conditions, the temperature of the thermal mass would increase substantially and take many days to cool down when a heatwave eventually passes.

While many regions in our southern states will have heating-dominated climates for decades to come (where more energy is used for heating than cooling), the following suggested measures will also help keep homes warm and so are prudent investments.

Read more about the importance of glazing, building design and appliances in preparing homes for heatwaves in ReNew 130.

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