Is your home ready for a heatwave?
Wed, 2nd Sep 2026 (Today)
We've had decades of experts telling us how to heat up our homes. Insulation, double glazing, heat pumps. Now we're being told we need to cool them down.
New research by Auckland Council has painted a picture of more frequent, and potentially deadly heatwaves, even under moderate climate change scenarios.
Think stinking hot homes and sweaty nights.
Some of the same features that help homes retain the heat can also help keep it out, but many of the features that enable us to intensify housing have done the opposite - leaving eaves off north-facing windows to maximise the building's site footprint and failure to incorporate adequate ventilation for example.
Auckland Council's Lead Climate Resilience Advisor, Petra Pearce, says even under a moderate climate warming scenario for the city we are looking at a jump from about 16 hot days in a summer (that's above 25 degrees) to 31 in 2050.
In terms of heatwaves, at the moment the longest run of hot days we get is around 3.7 days a season, and that could roughly double. That's a regional average so there are places that will be hotter.
"There's a lot of things we can do as a city to mitigate or reduce that 'urban heat island' effect," she tells The Detail. That's when hard surfaces such as concrete buildings and roads absorb the heat and release it overnight.
"And one of the best levers that we have is increasing green space and canopy cover. Auckland Council has a considerable programme of planting plants and trees, so council facilitates the planting of hundreds of thousands of plants and trees every year. So in 2025 for example council planted 480,000 trees and plants, and there have been about 2,000 large grade street trees planted every year since 2018. So there's a real focus on greening urban areas."
The council however is battling rules imposed from central government. In 2018 an Auckland Council report detailed the horrific loss of tree cover in the city's inner suburbs in the wake of legislation that stripped trees of bulk protection - more than 12,000 trees were chopped in the Waitematā board area alone since the laws gave developers and home owners open slather.
At the moment new Resource Management Act rules are going through Parliament, and will be in force before the election, that advocates say will make things even worse. Only urban trees with a historic heritage value will be protected, raising fears of cities being turned into concrete jungles.
"The research shows that if you have more green space, more canopy cover that provides shading and then that provides cooling," says Pearce. "Any large tree that is cut down definitely has an impact on our urban heat island mitigation efforts."
Pearce admits housing intensification is a "massive challenge", and "there is a lack of space for greening, particularly for those large trees".
One thing that may help is a part of the council's new Plan Change 120 where developers have to retain some deep soil and room on a site for large trees to be able to be planted. Soil scientists have warned that clear-felled developments are full of compacted soils which restrict water absorption and root growth.
BRANZ senior building physicist Stephen McNeil says there's no part of the building code that controls overheating at the moment.
"You've got some rules about daylighting… but nothing that actually controls overheating," he says.
"It's one of those challenges that we have yet to deal with. There's so many cases of people moving into new homes who are complaining about overheating or mould or other things like that."
The moisture expert says ventilation is key, and that's something that traditionally we haven't dealt with very well. Older homes may have 'accidental' ventilation where air comes in through gaps, but new well-sealed builds keep the cold out - and the moisture in.
"As we shift towards better-performing buildings we actually need people in the Building Code and the like to really deliberately think about how they're going to ventilate their house. And that's a different thing for the industry at the moment."
In June this year BRANZ released a study that found some New Zealanders were living in homes that were so cold in winter they could see their breath. But the same study also pointed to the emerging issue of overheating, finding that a quarter of bedrooms were above 24 degrees at 2am, meaning many homes are struggling to cool down overnight.
McNeil tells The Detail how we can retrofit our homes to mitigate some of those sweltering summer days and nights, including making sure there are eaves on north-facing windows, asking about thermal glass when replacing windows and ranch sliders, and making sure your drier vents to the outside.
