A more stringent meth-contamination testing regime will reduce unnecessary and expensive repairs to buildings, a Crown agency says.
International Accreditation New Zealand (IANZ) is implementing rules for testing buildings for methamphetamine contamination - rules which were brought in by Standards New Zealand two months ago.
The manufacture of methamphetamine can ruin buildings and the testing methods used in New Zealand have been notoriously unreliable for years.
The new standards limit acceptable contamination levels to 1.5 micrograms per 100cm squared.
Last year, Housing New Zealand was accused of evicting tenants based on poor assessments of the real risks.
IANZ chief executive Llew Richards said there were conflicts of interest in the past and property owners were often lumbered with expensive repairs.
"Problems have arisen in the past with the same companies testing properties and also providing cleaning services, a clear conflict of interest.
"That led to some property owners spending a small fortune, sometimes tens of thousands of dollars, on decontamination that wasn't actually necessary."
Dr Richards said the situation had improved.
"We have had more than 30 inquiries for accreditation for carrying out the proper inspection and testing of contaminated houses and looking at a clear process to ask if decontamination is really necessary," he said.
He said many testing companies previously relied on cheap, instant-answer test kits, of doubtful reliability, and buildings were sometimes decontaminated when they did not have to be.
It is not known how many buildings have been tested across New Zealand as a whole.
But Housing New Zealand said it carried out more than 1000 methamphetamine tests and had about 800 positive tests last year.
There were five evictions as a result.