The government's flagship KiwiBuild housing project could save millions of dollars if homes are built sustainably, a report says.
Commissioned by not-for-profit building organisation, the Green Building Council, the report says all 100,000 KiwiBuild homes should be built sustainably.
That would include factors such as energy efficiency, warmth, and the amount of building waste.
The report's author, economist Shamubeel Eaqub, estimated that if KiwiBuild homes were built to the 'Homestar 6' standard, New Zealanders could benefit by up to $330 million in the next 30 years.
The council has described Homestar as an independent national rating tool that measures the "health, warmth and efficiency of New Zealand houses". A home is rated on a scale from 6 to 10, it said, and houses with a rating of six or higher were "warmer, drier, healthier and cost less to run".
"If we are really building houses for first home buyers and low-income households then we want to make sure the houses we're building for them are not expensive to operate and expensive to keep healthy. Right now New Zealand is doing exactly that," the report said.
"We build homes that are not very healthy, that are difficult to heat, difficult to keep warm, difficult to get dry. We need to break the cycle and this is one way of doing it."
The report also noted building KiwiBuild homes sustainably could spur private developers to go green and decrease the additional cost.
"In the UK what we've seen is when the standards first come in they tend to be quite expensive to build because it's new, it's hard to source material, all those sorts of things. But over time that premium tends to shrink, generally over the course of five years."
Over time, Mr Eaqub said savings could be as high as $680 million if the costs decrease and 10,000 extra homes were built.
"Despite knowing that these higher standard, higher quality homes are good for your wallet and good for the community, it's not happening.
"The take-up rate is quite slow. I think there's a real opportunity with KiwiBuild to just show how quickly you can move the industry in terms of building up capability, to bring down those costs. And also to show the market this is something that people value."
In the next decade, Auckland's council-owned Panuku expects to build 10,000 homes to a Homestar 6 standard.
The Green Building Council said that had pushed other large developers to also consider the standard, with 25,000 houses currently in the works.
Chief executive Andrew Eagles said KiwiBuild was a massive opportunity for the government to live up to its emission promises and change the country's thinking about housing.
"With KiwiBuild we have a monumental, once in a lifetime opportunity to shift how we think about homes. So when you see 100,000 homes build to Homestar it clearly signals that this is possible and that others could be doing."
He acknowledged the government was being pressed to produce quantity but said quality was equally important.
"Wouldn't it be sad if in 10 years time we look at the homes we're building through KiwiBuild and we've got mouldy homes that have high energy bills and that are significantly behind where we could be?"
The report said New Zealand's Building Code was "recognised as being behind international standards," citing criticism from the OECD and International Energy Agency.
Mr Eagles said progressing standards could start with KiwiBuild for now.
"Then what happens is every sits up and says if this is possible why are we putting up with a sub-par building code because people can do this. Then you set a trajectory to a decent building code which considers overheating, which gives us good insulation in our homes.
Housing Minister Phil Twyford said it was too early to say whether the government would decide to build to the Homestar efficiency.
"Our big focus at the moment is on getting homes built initially and making sure they're affordable. But we'd be nuts if we didn't use this opportunity to build better quality homes, to increase the thermal efficiency, to reduce the lifetime cost of living in these houses."
He said staff were working on it and it was something he wanted the government to have a "serious look at".
"In all of those areas there's the opportunity to set new standards and I certainly want us to be at least better than code but let's see how ambitious we can be.
"We have to improve the quality and standard of housing in New Zealand and this whole area about thermal efficiency is central to it."
While being noncommittal about the Homestar standard, he said the built environment was one of the main ways the government could reduce carbon emissions to meet its net zero target by 2050.