Moisture Barrier

Healthy Homes Standards – Section 4: Moisture Ingress & Drainage

Did you know your rental property must have efficient drainage for the removal of stormwater, surface water, and groundwater? If your property has a closed-off sub-floor, it must have a ground moisture barrier. We think it’s obvious, but water can be a major source of dampness in a home. A damp home can lead to the poor health of your tenants, which can be destructive to the quality of your rental property.

Ground moisture barrier

What is a ground moisture barrier? It’s often a polythene sheet laid on the ground beneath your property. It can be purchase from most building retailers and installed by the homeowner, but we recommend you use a building professional to ensure it’s installed correctly.

Your ground moisture barrier must either be a polythene sheet and installed per section 8 of New Zealand Standard NS4246:2016, or have a vapour flow resistance of at least 50MNs/g and be installed by a professional installer.


There is only one exemption to the moisture ingress and drainage standard. The exemption covers properties where it is not reasonably practicable to install a ground moisture barrier. The Tenancy NZ website states that it is not reasonably practicable to install something if a professional installer cannot access the area without:

  • carrying out substantial building work
  • causing substantial damage to the property
  • creating greater risks to a person’s health and safety than is normally acceptable
  • it is otherwise not reasonably practicable for the professional installer to carry out the work

If you aren’t sure whether your property will pass this standard, we recommend you get in touch. Our experienced Healthy Homes inspectors on 0800 422 386 are available to help you with your investment property needs.