Rental properties which are already insulated will not be required to upgrade to modern standards, Housing Minister Nick Smith confirmed today.
A law change before Parliament will require all rentals to have ceiling and floor insulation installed by mid-2019, unless it is physically impossible to do so.
The Cabinet yesterday agreed to the levels of insulation which will be required.
One of the proposals in the draft regulations was a requirement for rentals which already had insulation to upgrade it to the new building standard, which was established in 2008.
The Government has now backed away from that proposal.
Dr Smith said the benefits were "marginal" and any costs would be passed on to tenants.
"This is well illustrated by the data on ceiling heat loss that shows the 1978 standard reducing heat loss by 83 per cent, the 2001 Building Code by 87 per cent and the 2008 Building Code by 92 per cent," he said.
Instead, rental properties would have to meet minimum standards for insulation, which were equivalent to the 2001 building standard.
Rental properties which currently have no insulation at all would have to upgrade to the new building standard.
Dr Smith said tenancy agreements would have to disclose the levels of insulation as an incentive to upgrade it over time.
The law change would also require landlords to install smoke alarms by July 1.
The insulation requirements were expected to affect 180,000 properties, while another 100,000 properties would be exempted because of the difficulties in accessing either ceiling or underfloor spaces.
Labour and the Greens want the Government to go further by introducing a Warrant of Fitness for rentals, which looked at a broader range of requirements.
• All rental properties must have insulation by 2019
• Properties with no insulation must be upgraded to the 2008 building standard
• Properties with existing insulation must meet minimum standard (2001 building standard)
• All rental properties must have smoke alarms by July 1