Healthy Homes Moisture Ingress and Drainage Standard NZ

What the Standard Covers

The moisture ingress and drainage standard under Regulation 27 and 28 of the Healthy Homes Standards has two parts: the property must have functioning drainage to remove water, and enclosed subfloor spaces must have a ground moisture barrier.

Moisture problems in rental properties cause mould, timber rot, and health issues that the Tribunal takes seriously. This standard is about preventing water from getting in and ground moisture from rising up.

Drainage: Gutters, Downpipes, and Discharge

Every rental property must have efficient drainage for removing stormwater, surface water, and groundwater. In practical terms:

• Gutters must be clear of leaves, debris, and blockages
• Downpipes must be connected and undamaged, directing water away from the building foundation
• Discharge drains must function — water should flow away from the property, not pool against walls or saturate the ground around foundations

This is not a one-time check. Gutters block seasonally, downpipes corrode over time, and drainage can be disrupted by building work or landscaping changes. The obligation is ongoing: you must maintain these systems throughout the tenancy.

Between tenancies is the natural time to inspect, but if a tenant reports a blocked gutter or leaking downpipe, the maintenance duty applies immediately.

Ground Moisture Barrier: The Subfloor Polythene

Enclosed subfloor spaces — the area between the ground and the underside of the floor — must be covered with a ground moisture barrier. The standard specifies heavy-duty polythene sheet installed to NZS 4246:2016.

The installation requirements are specific:

• Sheets must be laid continuously across the entire subfloor area
• Overlaps between sheets must be at least 75 mm
• Seams and edges at perimeter piles must be taped securely
• The barrier must sit directly on the ground, not draped over debris or uneven fill

A barrier that has torn, shifted off the ground, or been disturbed by plumbing or electrical work underneath is no longer doing its job. Check the subfloor from the access point and look for gaps, bunching, standing water on top of the polythene, or sections that have pulled away from the piles.

When You Cannot Install a Barrier

Some subfloor spaces are simply too tight to access. If clearance between the ground and the joists is too restricted for an installer to crawl through safely, Regulation 29 provides an exemption.

To claim this exemption, you need written confirmation from an experienced installer certifying that access is unsafe or not reasonably practicable. The report should detail the specific clearance measurements or structural hazards that prevent installation.

Keep this report in your evidence file for the tenancy and for at least 12 months after it ends, and declare the exemption on your Healthy Homes Compliance Statement. The exemption covers only the ground moisture barrier — it does not exempt the property from drainage maintenance, insulation, heating, ventilation, or draught stopping.

If the property undergoes future structural work that improves subfloor access, you should reassess whether the exemption still applies.

Documenting Moisture Compliance

Your evidence file for this standard should include:

• Dated photographs of the subfloor ground moisture barrier showing continuous coverage
• Photos of gutters, downpipes, and discharge points in working condition
• Any drainlayer certificates or sign-offs for drainage work
• Written installer reports if claiming a Regulation 29 exemption
• Maintenance records showing gutter cleaning and drainage checks

The NZ Healthy Homes compliance guide includes a property compliance filing structure that covers the moisture and drainage evidence you need for both the compliance statement and any future Tribunal enquiry.

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