Landlords asked to insulate rental properties are extremely reluctant to do so despite available subsidies, the Sustainability Trust says.
Under new legislation, ceiling and underfloor insulation will need to be retrofitted in social housing by July this year, and in all other rental homes by July 2019.
Just 4300 landlords have taken up insulation subsidies, despite a target of 20,000 houses by next June.
Sustainability Trust chief executive Phil Squire said his organisation sends letters to landlords with vulnerable tenants where properties are below building standards.
"Basically 'your tenant is vulnerable and your property falls well below the current RTA (Residential Tenancies Act) or building code standards and we have a 50 percent subsidy for you'.
"And the law will be in July 2019. I guess it's one of those things, reality beats rationality."
He said landlords were showing extreme reluctance despite the communication from the Sustainability Trust and subsidies that are available.
Landlords with low-income tenants or homeowners with low incomes can get 50 percent of the cost of insulation through the Warm Up New Zealand: Healthy Homes programme.
"It's possible a lot of landlords don't know. I think we have what we call accidental landlords out there. I would say professional properties and also those who are run by property managers should know about the law," Mr Squire said.
"And then to receive a letter... and a phone call from an organisation such as ourselves to directly offer you the subsidy and say that your tenants are struggling with health issues, then you'd have to say there's quite a bit of intransigence there."
He said the Trust has found many tenants are afraid of asking for insulation.
"They're in a very vulnerable situation in raising those issues. They might be faced with an increase in rent. It might already be a fragile relationship and so to raise that with the landlord can be problematic."