Short answer
Responsibility for mould generally follows the source of the moisture. If the mould is caused by water entering through a failure in common property — the building’s structure, external walls, roof or waterproofing — remediating the source and cleaning the mould is generally the owners corporation’s responsibility. If the building is watertight and the mould comes from how the inside of the lot is used, such as poor ventilation, it is generally the lot owner’s or tenant’s. Because the cause isn’t always obvious, an independent assessment often settles it.
Scenario A — the building’s problem (common property)
If the moisture causing the mould is entering because of a failure in the building’s structure or external envelope, it generally falls to the owners corporation to fix the source and clean up the mould.
Examples: rising damp through a concrete subfloor, water from a leaking roof structure, failing external window seals, or damp coming through an external brick wall.
The law: under section 106 of the Strata Schemes Management Act 2015 (NSW), the owners corporation must maintain and repair the common property. Where a failure of common property causes the mould, dealing with it is generally the scheme’s responsibility.
Scenario B — the resident’s problem (internal lifestyle)
If the building is watertight and the mould is growing because of how the interior of the apartment is being used, it is generally the lot owner’s or tenant’s responsibility.
Examples: windows kept permanently shut, not using the bathroom exhaust fan during hot showers, or drying wet laundry indoors in an unventilated room.
Action step for committees
Don’t guess. Where a resident reports significant mould, engage a licensed building inspector or industrial hygienist to test moisture levels. A professional report identifies whether the source is structural (common property) or atmospheric (internal use), which is usually what settles the argument — mirroring the same source question that decides water-leak responsibility.
Resolving it as a self-managed committee
Mould disputes turn toxic when there’s no clear record of the cause. A system such as Straita lets a self-managed committee log the report, attach the moisture assessment that identifies the source, track the remediation and hold the outcome — so responsibility rests on the evidence rather than accusation, and the history is there if the mould returns.
Primary sources
- Strata Schemes Management Act 2015 (NSW) — s 106, duty of the owners corporation to maintain and repair common property.
- NSW Government — Strata schemes (Fair Trading) — repairs, maintenance and common property.