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• Some of s terraced  are overheating, causing discomfort and potential .
• Large windows, poor ventilation, and lack of shade are primary causes, not insulation, experts say.
• A resident of a house that overheats every hot day tells the living in her home is like being in “an oven”.

Tens of thousands of Auckland families will suffer in overheating terraced houses and vulnerable people could risk unless our construction designs change, an industry body says.

tell the Herald overheating is difficult - and expensive - to mitigate once a house is built. Homes should be constructed to keep the heat out from the outset, they say.

Waterview resident Clara Lafont lives in a new build and tells the Herald it “gets ridiculously hot in the summer and cold in the winter”.

Lafont said: “The air doesn’t move. It genuinely feels like you’re walking into an oven.”

And the problem is being “locked in”,business development manager Matthew Cutler-Welsh says.

Auckland Council’s monthly housing update data for November showed 70% of building consents for dwellings were for townhouses, apartments, flats, units or other attached properties. Photo / Dean Purcell

Terraced houses are being built at pace in Auckland, with even more expected after the Government mooted 55,000 new ones to be fast-tracked through the consent process.

Auckland Council’s monthly housing update data for November showed 70% of building consents for dwellings were for townhouses, apartments, flats, units or other attached properties. The remaining 30% were standalone houses.

Cutler-Welsh believed the Building Code needed to be changed to mandate new houses be built to keep the heat out.

Construction Minister Chris Penk told the Herald, “I regularly hear concerns from the public about new homes overheating.”

Penk said these concerns were “a key reason why I asked my officials to investigate the new H1 Energy Efficiency [insulation] settings earlier in the year”.

Construction Minister Chris Penk (right) told the Herald, 'I regularly hear concerns from the public about new homes overheating.' Photo / Mark Mitchell

He wanted to see “if the recent changes are workable and not contributing to unintended consequences like overheating or unreasonable additional costs”.

Penk asked the Ministry of Business, Innovation and Employment to investigate the country’s new insulation standards in July.

But Penk’s speculation the stricter insulation requirements were causing overheating has been dismissed by experts who spoke to the Herald. The Green Building Council said rolling back H1 standards “goes against global best practice”.

Too much insulation not the problem, poor designs are, experts say: Sowhat’s the fix?

Large windows, a lackof eaves or other shade, no consideration of a property’s direction towards the sun and poor ventilation are causing overheating in old and new builds.

“Unfortunately, it’s a perfect recipe for overheating,” Cutler-Welsh told the Herald.

Large windows, a lack of eaves or other shade, no consideration of a property’s direction towards the sun and poor ventilation are causing overheating in old and new builds. Photo / Michael Craig

“We’re building homes with no shade or eaves, with windows that can never provide enough airflow to reduce overheating and no mechanical ventilation to compensate with fresh, cool air. We’re painting our homes and roofs dark colours which heat up quickly and absorb that heat through to the inside.”

He said there were limited steps to keep the heat out after a house was built and homes should be constructed with overheating in mind.

“Once a place is built a lot of the issues causing overheating are locked in,” Cutler-Welsh said.

“Our woeful Building Code doesn’t consider overheating at all. We’ve got no regulations protecting New Zealanders from overheating homes.

“We’ve just fast-tracked thousands of new homes, all of which face this possibility without action to improve our standards.”

Cutler-Welsh said there was a persistent “myth” about insulation causing overheating. He dispelled this, saying insulation should keep heat out.

He explained an insulated house as being like a chilly bin, keeping contents cool while the outside air temperature remains high.

“It’s an unfortunate myth that insulation causes overheating. In fact it’s the opposite – insulation is one of the key ways to avoid overheating," he said.

“Not enough insulation can allow heat to enter the home more easily.

“Overheating is primarily caused by large windows, often north facing, and poor ventilation. There’s a reason you don’t see clear or semi-transparent chilly bins.

Terraced houses are being built at pace in Auckland, with even more expected after the Government mooted 55,000 new ones to be fast-tracked through the consent process. Photo / Alex Burton

“The recent Auckland Council Medium Density Research shows overheating is an issue really impacting Kiwis. Without a requirement to reduce overheating, annually tens of thousands more families will have to deal with excessive temperatures for large parts of the year.”

The Building Research Association of New Zealand (Branz) corroborated the problem outlined by Cutler-Welsh.

“Overheating in new homes in New Zealand is becoming a growing issue,” the independent researcher said.

The way the house was built could cause it to overheat, “but the risk can be managed with good design”, Branz said.

It said in many houses being built there weren’t enough opening windows, or there were restrictions on how far they could open, making ventilation difficult.

“Housewide active ventilation can make a significant difference in managing indoor temperatures,” Branz said.

“Branz recommends mechanical ventilation in tandem with reasonable airtightness in new builds or major renovations.

“International trends show mechanical ventilation is becoming required in more jurisdictions. The additional costs of these systems are balanced by the benefit of improved health and comfort.”

Branz also said it was a “misconception that insulation causes overheating in homes in summer”.

Branz said: “In reality, the opposite is usually true. Roof spaces – the uninsulated spaces directly under the roof – routinely reach temperatures of 50-60+ degrees during the daytime and insulation above the ceiling level significantly reduces the flow of this heat into the dwelling."

‘It’s stale air ... and you just can’t do anything about it' - affected resident

Affected resident Clara Lafont says she can “feel it get hotter and hotter” as she climbs the stairs in her three-storey home.

“It is like stiff, stale air,” she said.

“I’ve been to Dubai before, and the house has just got that sort of oppressive heat feeling.

“And you just can’t do anything about it,” she said.

Lafont said she and her flatmates had tried different ways of cooling the house down, including closing the curtains on windows facing the sun and opening all windows and doors.

Affected resident Clara Lafont says she can feel it get hotter and hotter' as she climbs the stairs in her three-storey home. Photo / Michael Craig

“We’ve all got fans in our rooms, too, but that kind of just blows around the hot air,” Lafont said.

“And also, cold flannels on your head and on your wrists.

“But in terms of actually cooling down the core temperature of the house, it is extremely difficult, and even just last night, my cousin came and stayed and he couldn’t believe it. He said he had never been somewhere this hot.”

She said there were 20 other new builds on her cul-de-sac that had been completed at the beginning of 2024.

How to keep out the heat: Shade and ventilation

There are some steps people can take to keep the heat out, but “there’s by no means a catch-all silver bullet and many of the solutions won’t fix it entirely”, Cutler-Welsh said.

And some households’ options would be limited if they were renting or part of a body corporate, he said.

Below are some of the steps Cutler-Welsh advised:

• To reduce the amount of sun getting in;
• Ventilation;

Raphael Franks is an Auckland-based reporter who covers breaking news. He joined the Herald as a Te Rito cadet in 2022.