The Green Building Council says the Government's proposal to simplify insulation standards does not address the growing issue of overheating new builds.
Auckland Council researchers last year found the upper levels of terraced houses and semi-detached homes were so hot in summer they are almost unusable.
The Green Building Council's chief executive Andrew Eagles says there are increasing reports of new builds being saunas in summer with indoor temperatures as high as 50 degrees. He says that style of building made up about 45 per cent of the housing being built in the last year.
Mr Eagles says putting the design of a home into computer modelling systems to work out whether over heating would occur or not, would be a simple step. But he says the government is focusing on not adding any new costs to building.
