A stoush has broken out over new research that challenges whether green-certified homes are actually warmer, drier and healthier than typical new builds, as has been claimed.
The study by two Auckland University researchers measured indoor temperatures of 30 social houses including Homestar properties with a six-star rating compared to code compliant new builds and older homes.
During winter, the research found the Homestar-rated houses spent 56 percent of the time below the World Health Organisation's recommended temperature of 18 degrees.
The newly built code compliant homes dropped below that temperature 64 percent of the time - a difference the researchers say is statistically insignificant.
In summer, the six star-rated houses chronically overheated 75 percent of the time, compared to 58 percent of the time for the non-certified houses, the research showed.
The Homestar rating system run by the Green Building Council is supposed to measure the health and energy efficiency of a home. The council claims a six-star rating or higher means the home will be easier and more cost-effective to keep warm, healthy and more environmentally friendly than a typical new house built to the building code.
One of the researchers, Rochelle Ade, alleges that since sharing the results, which seriously challenge the rating system, the Green Building Council has been trying to undermine the study and her personal reputation.
"The Commerce Commission has just recently issued some environmental guidelines explaining how companies that sell products or services have to have evidence that backs up their claims if they're making claims around the environment," Ade told Checkpoint.
"In the context of green building, do those guidelines also apply to their claims? If the academic evidence that we have discovered shows that the six Homestar ratings weren't performing in the manner that is claimed, is that a breach of those guidelines and maybe a breach of the Fair Trading Act?," she said.
"It could be some serious implications for architects, engineers, banks, anybody who has been repeating these claims about six Homestar."
But The Green Building Council denies it is trying to undermine the research, and chief executive Andrew Eagles told Checkpoint he welcomes the information.
"That's interesting to see, it's useful to get that perspective. We'd like to see more research on that topic. It's really important to note that the tools are built up with a large group of community in the construction and property sector and this is one of the pieces of feedback," he said.
"I think it would be good if there was a larger number of properties and a wider range of property types [included in the research]."
In an email sent by the council to "valued partners" it questioned the integrity of the study and of Ade. It also asked recipients to keep the discussion document confidential.
"We were asked to provide comment back to some people who were looking at this so we put this report together to help inform them," Eagles said.
"Much of these concerns have already been dealt with in a tool that's going to be launched pretty soon."
But Eagles said the council was seeking to "have these conversations in a measured way," and that if the council wanted to undermine the research it would have made a public statement.
The council has also confirmed there is no independent research that supports the claims made about the homestar rating tool.