Strata Mould Problems: A Guide for Body Corporate and Owners

Mould in a strata building is rarely a simple fix. It involves multiple parties, overlapping responsibilities, and legislation that most owners have never read. Whether you are an owner dealing with mould in your unit, or a strata committee trying to manage a building-wide issue, understanding who is responsible — and what your obligations are — is the first step.

Common property vs lot property: who fixes what?

Under strata law, the responsibility for mould depends on where the mould is and what caused it.

Body corporate (owners corporation) responsibility

The body corporate is responsible for maintaining common property. In NSW, this is defined under the Strata Schemes Management Act 2015 and includes:

• Structural elements — external walls, roof, foundations, load-bearing walls
• Common area waterproofing — balcony membranes (in many cases), bathroom waterproofing in the original build
• Shared infrastructure — gutters, downpipes, stormwater drainage, common ventilation systems
• Common areas — lobbies, stairwells, parking garages, bin rooms, laundries

If mould in a lot (individual unit) is caused by a failure in common property — such as a leaking roof, defective waterproofing in the building envelope, or blocked common drainage — the body corporate is responsible for fixing both the cause and the resulting damage.

This is a critical point. Many strata committees attempt to argue that mould inside a unit is the owner's problem. If the root cause is a common property defect, it is not.

Lot owner responsibility

Individual lot owners are responsible for maintenance within their lot, which generally includes:

• Internal walls, flooring, and fixtures
• Plumbing fixtures (taps, showerheads, toilet cisterns)
• Ventilation within the unit (range hoods, exhaust fans they have installed)
• Maintenance of internal surfaces — cleaning, painting, and general upkeep

If mould in a unit is caused by the owner's failure to maintain their property — for example, not repairing a leaking tap or failing to ventilate adequately — it is the owner's responsibility.

The grey areas

Strata mould disputes frequently fall into grey areas:

• Bathroom waterproofing — in many buildings, the original waterproofing membrane is common property, but subsequent renovations may have made it the lot owner's responsibility. Check your strata plan and by-laws
• Balconies — some balcony structures are common property; the tiled surface may be the lot owner's to maintain. Water ingress through a balcony can affect the unit below
• Windows and sliding doors — the frame may be common property while the glass or hardware is the lot owner's responsibility. Condensation issues often arise here
• Exhaust fans and ventilation — original building ventilation is typically common property, but individual upgrades are not

When responsibility is unclear, the strata committee should seek legal advice or engage a building consultant before assigning blame.

NSW Strata Schemes Management Act obligations

The Strata Schemes Management Act 2015 (NSW) places clear obligations on the owners corporation:

• Section 106 — the owners corporation must maintain and keep in a state of good and serviceable repair the common property and any personal property vested in the owners corporation
• Section 106(5) — this duty applies even if the damage was caused by a lot owner, though the owners corporation may be able to recover costs
• Section 65 — lot owners must not carry out work that damages common property, and must maintain their lots so as not to create a hazard or nuisance

In practical terms, this means the body corporate cannot simply ignore a mould complaint that relates to common property, even if the mould is inside someone's unit. Failure to act can result in orders from the NSW Civil and Administrative Tribunal (NCAT) and potential liability for health-related claims.

Other states have similar legislation:

• Victoria — Owners Corporations Act 2006
• Queensland — Body Corporate and Community Management Act 1997
• Western Australia — Strata Titles Act 1985

The principle is consistent across jurisdictions: the body corporate must maintain common property, and mould caused by common property defects is the body corporate's responsibility.

How to report mould issues in strata

If you are a lot owner or tenant experiencing mould, follow a structured approach:

Step 1: Document the problem

• Take dated photographs of all visible mould, water stains, condensation, and any associated damage
• Note the location precisely — which walls, which rooms, proximity to common property elements
• Record any health symptoms being experienced by occupants
• Check with neighbours — if adjacent or nearby units have similar issues, it strongly suggests a common property cause

Step 2: Submit a written defect notice

Write to your strata manager or committee with:

• A clear description of the problem
• Photographs attached
• A request for inspection and repair
• Reference to the body corporate's obligations under Section 106 of the Act (in NSW)

Keep a copy of everything. Email is preferable to verbal communication because it creates a dated record.

Step 3: Request a common property inspection

Ask the strata committee to engage a qualified building inspector or mould assessor to determine the cause. This should not be a general handyman — it should be someone with experience in moisture diagnostics and mould investigation.

The inspection should identify:

• The species and extent of mould growth
• The moisture source (leak, condensation, rising damp, ventilation failure)
• Whether the cause is a common property defect or a lot maintenance issue
• Recommended remediation scope

Step 4: Follow up and escalate if necessary

If the strata committee does not respond within a reasonable timeframe (generally 14–28 days for non-urgent matters):

• Submit a formal motion for the next strata meeting to address the issue
• Apply for mediation through NSW Fair Trading (free service)
• Apply to NCAT for an order compelling the owners corporation to carry out repairs

Lot owners should not feel they need to accept inaction. The legislation provides clear mechanisms for resolution.

Building-wide mould assessment

In multi-unit buildings, mould in one unit often indicates a systemic problem. Water travels through concrete, along pipes, and through shared wall cavities. A leak on level five can cause mould on level three.

Strata committees dealing with multiple mould complaints should consider a building-wide assessment. This involves:

• Thermal imaging — identifies hidden moisture within walls and ceilings without destructive investigation
• Air quality testing — measures airborne spore levels in common areas and affected units
• Moisture mapping — systematic measurement of moisture levels throughout the building
• Root cause analysis — identifying whether issues stem from building defects, maintenance failures, or design inadequacies

A building-wide approach is more cost-effective than addressing individual complaints reactively, and it provides the strata committee with a clear scope of works and budget for remediation.

Professional documentation

Proper documentation protects the body corporate, the lot owners, and any tenants involved. Professional mould reports should include:

• Scope of contamination — species identified, areas affected, severity rating
• Root cause identification — with photographic and instrumental evidence
• Remediation recommendations — specific, costed, and prioritised
• Responsibility allocation — based on the findings, which party is responsible for which aspect
• Ongoing monitoring recommendations — particularly for systemic issues

This documentation is essential for insurance claims, NCAT applications, and internal strata decision-making.

Prevention strategies for multi-unit buildings

Preventing mould in strata buildings requires attention at both the building and individual unit level.

Building level (body corporate responsibility)

• Maintain waterproofing — regular inspection and maintenance of roof membranes, balcony membranes, and the building envelope
• Clear drainage — gutters, downpipes, and stormwater systems should be cleared at least annually
• Ventilate common areas — ensure car parks, bin rooms, and common laundries have adequate ventilation
• Address defects promptly — water ingress issues do not improve with time. Early intervention is always cheaper
• Include mould in the maintenance plan — proactive inspection is cheaper than reactive remediation

Unit level (lot owner responsibility)

• Ventilate daily — open windows, use exhaust fans, avoid drying clothes indoors without ventilation
• Report leaks immediately — even small drips. A slow leak behind a wall can cause extensive mould growth within weeks
• Maintain bathroom seals — re-grout and re-seal as needed to prevent water penetrating behind tiles
• Monitor humidity — keep indoor relative humidity below 60%

Need a strata mould assessment?

At Pureairo, we work with strata committees, property managers, and individual lot owners across Sydney. Our commercial and strata services are designed specifically for multi-unit buildings. Our assessments provide the clear, documented evidence needed to identify responsibility, scope remediation, and resolve disputes.

We use SAN-AIR technology — a natural, non-toxic treatment system — which is particularly well-suited to multi-unit environments where chemical treatments can affect neighbouring residents. If your building has a mould problem, get in touch for a professional assessment and a clear path forward.