The Ministry of Business, Innovation and Employment is warning landlords that they are risking fines if they fail to tell tenants about insulation at their property.
Landlords have been required to give specific details about a property's insulation on all tenancy agreements signed since July 1, 2016.
MBIE said its Tenancy Compliance and Investigation Team had undertaken 24 investigations into incomplete insulation statements as of May this year.
One landlord was successfully prosecuted, and 15 warnings have been given out, but MBIE spokesperson Michael Docherty said it's an issue which will face increased scrutiny in future.
"The TCIT has found a lack of adequate insulation statements were common when undertaking a recent audit of 55 landlords," Mr Docherty said.
One tenancy agreement seen by 1 NEWS, issued by a large Auckland property management company and signed this year, simply stated that insulation was "unknown - to be inspected".
"Merely stating that insulation is 'unknown' is a breach of [their] obligation," Mr Docherty said.
"If landlords are genuinely unable to establish the information they need to provide, then they need to set out what information in missing and what steps they have taken to obtain this information.
"All reasonable efforts must be made to obtain the necessary information to do this, including assessing the building, engaging a professional to do an assessment and/or checking the council building file."
The maximum fine which can be given to landlords who fail to provide insulation information is $500.
Ceiling and underfloor insulation will be required in all rental properties by July 1 next year, and MBIE warns that Tenancy Services will be cracking down on enforcement in this area.
"Tenancy Services are treating insulation statements as a priority area and are taking stronger action where breaches are found," Mr Docherty said.