How to keep your house cool in a heatwave

If overnight temperatures are due to fall below your inside temperature, open the house as much as possible from late afternoon. Image from shutterstock.com

Should you open or close your house to keep cool in a heatwave? Many people believe it makes sense to throw open doors and windows to the breeze; others try to shut out the heat. Listen to talk radio during a hot spell and you are likely to hear both views.

In a modern house the best advice is to shut up shop during the heat of the day, to keep the heat out. Then, throw open the windows from late afternoon onwards, as long as overnight temperatures are lower outside than inside.

But our research shows that opening and closing doors, windows and curtains is just one of the factors at play. To really stay cool when the heat is on, you also need to think about what type of house you have, and what its surroundings are like.

The traditional “Queenslander” house has long been seen as ideally suited for hot weather. Such houses have great design features for cooling, including shady verandas and elevated floors. But the traditional timber and tin construction provides very little resistance to heat transfer.

If uninsulated homes are closed up during a heatwave they would very likely become too hot. This has led people to opening up their house, to stop them getting much hotter inside than outside.

But in temperatures of 40C and above, one could argue that both strategies (opening and closing) in an uninsulated house would result in very uncomfortable occupants. Such houses would also not meet current building regulations, as insulation has been required in new houses since 2003 (or earlier in some parts of Australia).

Our research explores the role of design and construction on occupant comfort in hot weather. We have looked at brick and lightweight houses, as well as those made from less common materials such as structural insulated panels, earth, straw, and advanced glass and roof coatings.

We found that three factors influence the comfort of people inside a house: whether is it opened or closed; its urban context; and its construction materials. Having a better understanding of these factors could help you to keep cool this summer – or prepare for the next one.

To breeze or not to breeze

Whether they have air-conditioning or not, we found that people usually approach hot weather in the same way: by opening doors and windows to capture breezes.

People in both groups also tended to shut up the house if it gets hot outside, or if there is no breeze, or before switching on the air-conditioner if they have one. Most participants in our survey, which looked at homes less than 10 years old, also used ceiling fans to create air movement.

Occupants tape foil to the inside of windows to try to stop their home from overheating in Queensland.