Industry experts are asking the building minister to consider what they say is an affordable way to prevent new homes overheating.
Emails released under the Official Information Act show Building and Construction Minister Chris Penk wants to roll back upgraded insulation standards, after complaints from builders and developers that the H1 standards under the Building Code were adding tens of thousands in costs and making homes too hot.
The H1 standards were expected to save an average, new four-bedroom home an estimated 40 percent on heating, but Penk told government officials he was "keen to move forward" with work on returning energy efficiency requirements to their previous state, where they had sat for 10 years before being changed just over a year ago.
The minister says government officials are "urgently" investigating how costs have changed under the new standards.
When it comes to overheating, building experts say the problem is not insulation, but poor design and failing to model the impact of features like huge, north-facing windows.
Architect Tim Ross said architects overwhelmingly supported upgraded standards, and design flaws such as over-glazing, under-shading of windows and poor ventilation were to blame for overheating.
"A lot of the buildings that people are complaining about were constructed well before the H1 changes came into force and it's just to do with the fact we don't have anything in the Building Code that prevents over-glazing and over-heating.
"There's a whole bunch of things that can be done, but the Building Code doesn't require any level of energy modelling."
He said modelling performance before the building stage would not be a big cost.
"One you know how to do it, we're talking a few hours to prepare an energy model which would prevent overheating."
Architecture and Design Professor Robyn Phipps of Victoria University likened installing huge areas of unshaded glass to sitting in direct sun in summer and expecting to stay cool.
She said insulation helped keep homes cool in summer, and warm in winter.
"Just like if you put your picnic in a chilly bin it will stay cooler when you go to the cricket, the insulation will keep your house cooler, but it's the windows - too much glass, wrong orientation - which are letting the heat in," she said.
"There are some very good, easy-to-use tools around which will help with the energy modelling. It's not a big cost at all."
Architects told RNZ that if spectacular views justified putting a big window on the sunny side, modelling could tweak the rest of the home so it met the standards, and did not overheat.
New Zealand Certified Builders chief executive Malcolm Fleming said overheating - and unnecessary building costs - can arise when builders and designers simply bolster every aspect of a home to meet the H1 standards individually for items such as ceiling insulation and windows, rather than modelling the whole home and how parts will work together.
That can lead to homes being over-specced, over-hot and costlier than they needed to be, he said.
He said some designers and builders needed training on how to use a more flexible approach, adjusting components to meet the standards overall.
Fleming said building industry science group BRANZ had debunked the idea insulation made homes too hot.
"BRANZ has just come out and said insulation does not cause overheating in homes, it's a common misconception but... it's just not true."
He said Certified Builders had offered to work with the minister to tweak the rules, to reduce costs without getting rid of improvements.
Several other industry groups have come out in support of keeping the standards.
The Insulation Association said the standards encouraged better insulation in renovations as well as new homes, lifting the performance of cold and draughty older housing stock when newer parts were built in accordance with the new code.
"There has been a long lead in for the H1 changes and the industry has made significant investment in preparation for these changes. Any changes at this point will knock investment confidence and create disruption and risk to the industry as a whole," the association's Richard Arkinstall said in a statement.
Master Builders declined to answer a question about whether it had lobbied for the rollback.
Fletcher Building has clarified that it did not lobby for the roll back of the home insulation standards, after the minister named the company among those whose representatives were complaining about the standards, in an email he sent to officials.
A spokesman for the company said it had always advocated for improved building performance.
As well as complaints made directly to the minister, the Ministry for Business, Innovation and Employment received what it described as a large number of complaints from individual developers and builders about the changes when it surveyed the state of the industry.
