From mid-2019, all rental properties must be insulated.

The Government will begin fining landlords for not insulating their rentals the second a new law comes into play next year.

However, the Insulation Association of New Zealand is concerned it did not have the resources to check all 100,000 properties.

Association executive Richard Arkinstall​ said he had raised concerns with the Ministry of Business, Innovation and Employment (MBIE) over its ability to audit the vast number of properties by mid-2019.

The Residential Tenancies Act (RTA) amendment, requiring all rentals to have insulation in ceilings and under floors, would be enacted in July next year.

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"We are yet to see the definitions and the boundaries of how they're going to know if all 100,000 rental properties have been done [insulated]," Arkinstall said.

When the amendment was announced in 2016, MBIE set up a taskforce to oversee it, named the tenancy compliance and investigations team.

Team national manager Steve Watson said its mandate was to "investigate serious breaches of the RTA that pose a serious risk to the health of vulnerable tenants, where landlords persistently fail to meet their obligations".

From July 1 next year, his staff would begin "targeting landlords to ensure that they have met their obligations to have insulation installed".

Landlords who did not comply with the new law could be fined penalties of up to $4000 by the Tenancy Tribunal, he said.

He called the move "proactive," however, Arkinstall said MBIE could begin auditing properties before the law came into effect.

Insulators had carried out more insulation inspections of rental properties since 2016, but it had not installed more insulation than usual, Arkinstall said.

Landlords were running out of time to have insulation installed as the industry headed for a peak winter season, he said.

Watson suggested there would be no excuses accepted for landlords who had not met the legal requirements by next year.

"Landlords have known since the Residential Tenancies Act 1986 was amended on 1 July 2016, that they had three years to ensure that they meet the new standards for insulation that must be present in all rental properties from 1 July 2019."

The new law required insulation to be installed where "reasonably practicable" in all income-earning rental properties at the landlord's cost.

All new tenancy agreements made after the law was first announced in July 2016 were required to include insulation statements.

Such statements had to disclose if the property was insulated and if it was, where, its type and condition.