Moisture ingress and drainage standard
Rental properties must have efficient drainage for the removal of storm water, surface water and ground water. Rental properties with an enclosed sub-floor space must have a ground moisture barrier.
Moisture can be a large source of dampness in a home. This dampness can lead to poor health outcomes for tenants and can be destructive to the quality of a house.
All private rentals must comply within 90 days of any new or renewed tenancy after 1 July 2021, with all private rentals complying by 1 July 2024. All boarding houses must comply by 1 July 2021. All houses rented by Housing New Zealand and registered Community Housing Providers must comply by 1 July 2023.
What is the moisture ingress and drainage standard?
Rental properties must have efficient drainage for the removal of storm water, surface water and ground water, including an appropriate outfall. The drainage system must include gutters, downpipes and drains for the removal of water from the roof.
If the rental property has an enclosed subfloor, a ground moisture barrier must be installed if it is reasonably practicable to do so.
Our guidance document has more specific information on the moisture ingress and drainage standard.
Download the moisture ingress and drainage guidance document. [PDF, 1.5 MB]
Ground moisture barrier
A ground moisture barrier is generally a polythene sheet that can be bought from most building retailers. It can be installed by a house owner or a building professional.
Ground moisture barriers must either:
- be a polythene sheet and installed in accordance with section 8 of New Zealand Standard NZS4246:2016 [PDF, 6 MB], or
- have a vapour flow resistance of at least 50MNs/g and be installed by a professional installer.
Exemptions to the moisture ingress and drainage standard
There is one specific exemption to the moisture ingress and drainage standard. This exemption covers properties where it is not reasonably practicable to install a ground moisture barrier.
It is not reasonably practicable to install something if a professional installer can’t access the area without:
- carrying out substantial building work, or
- causing substantial damage to the property, or
- creating greater risks to a person’s health and safety than is normally acceptable, or
- it is otherwise not reasonably practicable for a professional installer to carry out the work.
General exemptions to the healthy homes standards
Further information
The moisture and drainage standard is one of five healthy homes standards.
Find out about the other healthy homes standards:
