Building rules are being changed to double the minimum amount of roof insulation required for new houses across the country.
The new-build requirements, to be introduced over the next two years, vary according to which of six new climate zones a house is in. Photo: RNZ / Nate McKinnon
The Ministry of Business, Innovation and Employment is calling it the biggest boost to Building Code energy efficiency rules in over a decade.
Windows will also have to be able to hold more heat in.
Officials said the new requirements would reduce the energy needed to heat homes by up to 40 percent.
The requirements, to be introduced over the next two years, vary according to which of six new climate zones a house is in.
"There will be a one-year transition period for the majority of the changes and a two-step approach for the window insulation requirements which will allow the sector to prepare for the changes before they become mandatory for new builds," said manager of building performance and engineering Jenni Tipler.
The higher insulation requirements could be met with current design and construction practices, the ministry said in a report.
"This addresses concerns in the submissions about the implementation of larger shifts and enables faster transition times with less adverse effects on existing supply chains."
Not so, however, when it comes to walls.
Some submitters wanted the standard wall framing depth increased from 90mm to 140mm, or other improvements.
But timber supply issues and design changes to how walls were framed under any new rules, posed difficulties, the report said.
"That is why we have left the requirements for walls in residential building mostly unchanged."
More research on new construction methods was needed before wall rules were changed, the report stated.
The ministry also promised to lay out protocols about how it would ensure the stronger rules were followed.
It had had more feedback on these proposed changes than for any other change to the Building Code in years, the ministry said.
The changes would support the sector in helping the country get to net zero carbon emissions by 2050, Tipler said.