Mould in NZ Rentals: Who Is Responsible and What You Must Do

Mould is one of the most common maintenance disputes in NZ rentals, and it is one of the most misunderstood. Many landlords assume mould is always the tenant's fault because they are not ventilating. Many tenants assume mould is always the landlord's fault because it is a structural issue. The truth is that it depends entirely on the cause, and the law treats structural mould and behavioural mould very differently.

This guide covers who is responsible for what, what the Healthy Homes Standards require, and how to handle disputes without ending up at the Tenancy Tribunal.

The Basic Distinction: Structural vs Behavioural Mould

Structural or systemic mould is caused by defects in the building itself:

• Water ingress through the roof, walls, foundations, or around windows
• Rising damp from the ground
• Inadequate insulation causing cold surfaces where condensation forms
• Broken or missing ventilation systems (HRV units, rangehoods, bathroom extractors)
• Leaking pipes behind walls or under floors

This is the landlord's responsibility. If mould exists because the building cannot keep moisture out or adequately ventilate, the landlord must fix the underlying cause, not just clean the mould.

Behavioural mould is caused by how the tenant uses the property:

• Drying laundry indoors without opening windows or using a heat pump
• Cooking or showering without using extractor fans or opening windows
• Blocking ventilation vents
• Keeping internal temperatures too low (cold surfaces attract condensation)

This is the tenant's responsibility to manage. A landlord who fixes a mould problem caused by the tenant's behaviour may be able to claim the remediation cost from the tenant if it constitutes damage beyond fair wear and tear.

Why It Is Almost Never Simple

In most real-world mould disputes, both factors are present. A property with poor insulation makes it very hard for a tenant to keep condensation under control even with good ventilation habits. A well-insulated property can still develop mould if the tenant never opens windows.

The Tenancy Tribunal generally looks at proportional responsibility. A landlord who has not insulated the property to Healthy Homes Standards will find it hard to blame the tenant entirely for mould. A landlord who has insulated and installed adequate ventilation can more credibly argue that the tenant's behaviour is the cause.

What the Healthy Homes Standards Require

The Healthy Homes Standards set minimum requirements for:

• Heating: A fixed heater capable of heating the main living room to 18 degrees Celsius. This is directly connected to mould - a warm property condenses less moisture.
• Insulation: Ceiling and underfloor insulation to required standards. Uninsulated ceilings are cold surfaces where condensation accumulates.
• Ventilation: Extractor fans in kitchens and bathrooms that vent to outside, and opening windows in all habitable rooms. This is the key Healthy Homes requirement for mould prevention.
• Draught stopping: Gaps and holes in floors, walls, ceilings, and around doors that cause cold air infiltration must be blocked.
• Drainage: Adequate drainage from gutters, downpipes, and around the building.

All private rentals must have been compliant with these standards since 1 July 2025 (extended deadlines for some existing tenancies). If your property is not compliant, your position in any mould dispute is significantly weaker.

What You Must Do When Mould Is Reported

When a tenant reports mould, you have legal obligations under both the general condition of the property requirements and Healthy Homes:

1. Inspect promptly. Do not wait weeks to respond to a mould complaint. Go and see it, or arrange for someone to.
2. Identify the cause. Look for water ingress, check the ventilation systems are working, check insulation.
3. Fix any structural causes. If there is water getting in or ventilation is broken, fix it. This is not optional.
4. Remediate the mould. Clean visible mould with an appropriate cleaner. In serious cases, professional remediation may be needed.
5. Communicate to the tenant about ventilation practices if behavioural factors are contributing. Put this in writing.

Ignoring a mould report is a significant risk. The Tenancy Tribunal has awarded exemplary damages to tenants where landlords repeatedly ignored mould complaints that were making the tenant's family ill.

Mould and Health

Mould is a serious health issue, particularly for children, elderly people, and those with respiratory conditions. The RTA's general obligation to provide and maintain the property in a reasonable state is increasingly interpreted through a health lens since the Healthy Homes Standards came into force.

If a tenant has a young family or someone with asthma in the household and you ignore mould, you face not just Tribunal proceedings but potential liability for health impacts.

Documenting Mould: Why It Matters

Documentation is everything in a mould dispute:

• If a tenant reports mould, respond in writing so there is a record of your response
• If you inspect and find behavioural mould, write to the tenant noting what you observed and what ventilation practices you expect
• If you remediate mould caused by the tenant, document the cost so you can claim it from bond if needed
• Move-in inspection photos showing the property was mould-free are your evidence that any mould that develops is not pre-existing

When the Tenant Claims Compensation

If a tenant claims compensation for mould damage to their belongings or for living in substandard conditions, the Tribunal will ask:

• Was the property compliant with Healthy Homes Standards?
• Did the landlord know about the mould and fail to act?
• Did the landlord fix the structural causes when they were identified?
• Was the mould primarily caused by the landlord's failure or the tenant's behaviour?

If you have maintained the property to standard, responded promptly to complaints, and documented everything, you are in a much stronger position even if the Tribunal finds some partial responsibility.

The RentManager Approach

Managing mould issues requires keeping clear records of maintenance requests, responses, and outcomes. RentManager gives you a maintenance log attached to each property and tenancy, so when a dispute arises, you have a complete documented history of what was reported, what was done, and when — all in one place rather than scattered across email threads and text messages.