Strata Mould Responsibility: Who Pays for Remediation?

Mould in a strata building raises one question faster than any other: who pays?

The answer depends on where the mould is, what caused it, and whether the source is common property or within an individual lot. Get it right and the issue gets resolved. Get it wrong and you're heading for a tribunal hearing, months of delay, and a much bigger remediation bill.

This guide breaks down the rules for NSW strata buildings. Other states follow similar principles, but specific legislation varies.

The basic rule: common property vs lot property

Under the Strata Schemes Management Act 2015 (NSW), the owners corporation (body corporate) is responsible for maintaining and repairing common property. Individual lot owners are responsible for their own lots.

Common property includes:

• External walls, roof, and foundations
• Common area corridors, lobbies, and stairwells
• Shared plumbing, drainage, and waterproofing membranes
• HVAC systems serving common areas
• Balcony structural slabs (in most schemes)

Lot property includes:

• Internal walls, ceilings, and floors within the lot
• Internal plumbing fixtures
• Appliances and fixtures installed by the owner
• Internal paintwork and finishes

Who pays: four common scenarios

Scenario 1: Mould from a common property defect

The owners corporation pays.

If mould in a unit is caused by a leaking common property pipe, failed roof waterproofing, rising damp through common walls, or inadequate common area ventilation — the body corporate is responsible for both fixing the defect and remediating the mould.

This is the most common scenario in older strata buildings. Water ingress from common property creates moisture inside individual lots, and mould follows.

What to do: Report the issue to your strata manager immediately. Request a plumber's report or building inspection to confirm the moisture source is common property. The owners corporation should then engage a professional remediation service.

Scenario 2: Mould from a lot owner's failure to maintain

The lot owner pays.

If mould results from a lot owner's failure to maintain their own property — a leaking internal shower, broken exhaust fan, or failure to ventilate — the owner bears the cost.

In practice, this can be difficult to prove. If the owner disputes the cause, an independent moisture assessment is usually needed.

Scenario 3: Mould from tenant behaviour

The lot owner pays (initially), with potential recovery from the tenant.

If a tenant causes mould by consistently failing to ventilate, blocking exhaust fans, or drying clothes indoors without ventilation, the lot owner is still responsible for remediation. The owner may recover costs from the tenant through the bond or tribunal, but the body corporate is generally not liable.

Scenario 4: Mould in common areas

The owners corporation pays.

Mould in corridors, stairwells, parking areas, plant rooms, or any common area is the body corporate's responsibility. This includes mould in common HVAC systems that affects air quality throughout the building.

For guidance on HVAC-specific issues, see our article on HVAC mould in commercial buildings.

The grey areas

Real strata mould disputes are rarely clean-cut. Here are the situations that generate the most conflict:

Concurrent causes. What if a common property leak is part of the problem, but the tenant also fails to ventilate? Both parties may share responsibility. Typically, the owners corporation must fix the common property defect regardless.

Waterproofing failures. In many buildings, the waterproofing membrane sits at the boundary between common and lot property. Courts have generally held that the membrane is common property, making the body corporate responsible for its failure.

Ventilation design. If a building was designed with insufficient ventilation — internal bathrooms without exhaust, no cross-ventilation, sealed building envelopes — this is arguably a common property issue even if the mould appears inside individual lots.

Historical neglect. If the body corporate knew about a water ingress issue for years and failed to act, they may be liable for the resulting mould damage to lot contents and finishes, not just the structural repair.

How to resolve disputes

Step 1: Document everything

Before anything else, document the mould and moisture:

• Photograph all visible mould
• Note the date you first observed it
• Record any musty odours or water stains
• Keep copies of all communications with strata management

Step 2: Get a professional assessment

A professional mould assessment identifies the species, concentration, and — critically — the moisture source. This evidence is essential for determining responsibility.

At Pureairo, our mould testing reports are designed for strata compliance. They clearly document the contamination scope, moisture source, and recommended remediation approach.

Step 3: Request action through proper channels

Write to your strata manager (not just a phone call) requesting investigation and remediation. Reference the specific by-law or legislation. Keep copies.

If the owners corporation is responsible and fails to act, you can:

1. Issue a formal notice through your strata manager
2. Apply for mediation through NSW Fair Trading
3. Apply to NCAT (NSW Civil and Administrative Tribunal) for orders

Step 4: Don't wait

Mould spreads. A small patch behind a bathroom vanity can become a building-wide contamination issue within weeks if the moisture source isn't addressed. Early action is always cheaper than delayed remediation.

What strata committees should do

If you're on a strata committee, take mould reports seriously:

• Investigate promptly — delay creates liability
• Engage qualified professionals — not a handyman with bleach
• Fix the moisture source first — remediation without fixing the cause is wasted money
• Document the resolution — keep records for future AGMs and potential disputes
• Consider a building-wide assessment — if one unit has mould from a common property issue, others likely do too

Pureairo works with strata committees and property managers across Sydney to provide building-wide mould assessments and remediation programs. Our reports meet strata compliance standards and support cost allocation decisions.

Key takeaways

• Common property defect = body corporate pays. This includes waterproofing, shared plumbing, and ventilation design.
• Lot owner's failure to maintain = lot owner pays. Internal plumbing, fixtures, and maintenance.
• Get professional evidence early. A moisture assessment that identifies the source saves months of dispute.
• Document everything. Written records are essential if the matter escalates.
• Act fast. Mould doesn't wait for committee meetings. Every week of delay increases the remediation scope and cost.

Need help with a strata mould issue? Contact us for a free assessment — we'll identify the source, document the contamination, and provide a report that supports fair cost allocation.