BLUF answer
Mould in an NSW strata unit is commonly a responsibility question before it is a remediation question: is the source in common property (the owners corporation’s responsibility) or within your lot (your responsibility)? The answer depends on the specific strata plan, the type of building element involved, and sometimes on the strata by-laws. This guide explains the practical framework. It is not legal advice, and specific disputes should be directed to a strata lawyer or to NCAT. Our mould inspection and testing service can provide an independent assessment of source and extent in an Illawarra strata context, which is often the first step in resolving a responsibility question.
Common property vs lot property: the basics
In an NSW strata scheme, the building is divided between lot property (which individual owners own) and common property (which the owners corporation owns and is responsible for maintaining).
The boundary between the two is defined by the strata plan for each scheme, and it varies. As a general rule under the Strata Schemes Management Act 2015:
- External walls, roofs, structural elements, and the building’s common areas are typically common property
- Internal surfaces of external walls (paint, plasterboard lining) and interior fittings within the lot are typically lot property
- Windows, balconies and building services (water, drainage) often fall in grey areas that depend on the specific strata plan
The practical consequence for mould: if water is entering your apartment through the external facade, a leaking roof, or a failing balcony waterproofing membrane, the owners corporation is generally responsible for the source. The mould inside your lot that resulted from their failure to maintain common property is a repair the owners corporation should also address.
If the mould in your apartment is caused by a plumbing leak inside your lot, condensation from your own inadequate ventilation, or your own internal shower waterproofing failure, that is your responsibility as the lot owner.
NSW Fair Trading, strata living is the starting point for understanding your rights and the owners corporation’s obligations in NSW.
Bathroom stacks, balconies and windows
Three building elements cause the most strata mould disputes in Illawarra apartment buildings.
Shared bathroom drainage stacks. In multi-storey apartments, the main drain stack running vertically through the building is usually common property. Leaks from that stack, or from the connections between lot plumbing and the stack, can cause mould in multiple lots and in common wall cavities. Determining whether a specific joint is the owner’s plumbing or the common stack usually requires a licensed plumber’s assessment, which the owners corporation should arrange.
A practical hazard that often goes unnoticed: bathroom exhaust fans in apartments built before around 2000 commonly vent into the common ceiling void rather than to the exterior. This fills the void with humid air, creates mould in the ceiling space, and can cause mould to appear on ceilings throughout the building. The venting system is usually common property, and correction is the owners corporation’s responsibility.
Balconies. Balcony waterproofing is a recurring mould source. Where water penetrates a balcony membrane and enters the lot below or the common ceiling, the membrane is generally common property. Water from your balcony that enters your own lot because of a cracked tile or poor drainage is more likely your responsibility. If water from an upstairs neighbour’s balcony is entering your lot, both the neighbour and the owners corporation may have responsibilities depending on the specific element that failed.
Windows. Window frames and glazing in strata buildings are often assigned to common property but the position varies by scheme. If water is entering around window frames during rain, the owners corporation should be notified and should arrange repair. A roof leak or failed window flashing causing mould inside your apartment is generally a common property responsibility.
When water enters from another lot
Water entering your lot from an adjacent or upstairs lot is one of the most contested scenarios in strata mould. The responsible party depends on where the failure occurred.
If the upstairs neighbour’s shower waterproofing has failed and water is coming through your ceiling, the upstairs lot owner is generally responsible for fixing the waterproofing (their internal fitting) and may be liable for damage to your lot. If the failure is in a pipe within their lot, they are responsible.
Document the mould and water ingress in your lot thoroughly. Our tenant photo evidence guide covers the documentation approach that also applies to lot owners in disputes. Contact the owners corporation in writing and request that they facilitate an assessment.
For strata tenants, the chain of responsibility runs from your landlord (the lot owner) who in turn makes claims on the owners corporation where applicable. The mould in rentals NSW guide and landlord mould checklist cover the tenant-landlord dimension of this.
What the owners corporation should do
When mould in a strata lot is caused by common property, the owners corporation has a general duty to maintain and repair common property in good condition. In practice, this means:
- Responding to written notice within a reasonable time
- Arranging a qualified assessment of the source
- Engaging a licensed contractor to fix the common property defect
- Addressing the resulting mould in the lot if the damage was caused by their failure to maintain common property
Owners corporations in Wollongong CBD apartments and North Wollongong buildings have faced increasing pressure on these issues as older buildings from the 1980s and 1990s have weatherproofing systems nearing the end of their service life.
Where the owners corporation is unresponsive, the escalation path is NCAT (NSW Civil and Administrative Tribunal) for strata disputes. A lawyer or strata agent can advise on the NCAT application process. Consult them before withholding levies or taking unilateral action.
If you need an independent inspection report to support a claim against the owners corporation, our mould inspection service provides documented assessments with moisture readings and source identification that are useful in these disputes.
What a tenant in a strata unit should do
A tenant in a strata apartment deals with their landlord (the lot owner) in the first instance. The landlord is responsible for the lot being fit for habitation and for repairing defects that affect the tenancy, even where the underlying cause is a common property issue that needs to be resolved with the owners corporation.
From a practical standpoint:
- Report mould in writing to your property manager or landlord, with photos and dates
- Request repair within a reasonable time
- If the source appears to be common property (roof, external wall, shared plumbing), the landlord should notify the owners corporation
- If the landlord is unresponsive, escalation is through NSW Fair Trading’s tenancy division
See our guides on mould in rentals NSW and documenting mould evidence as a NSW tenant for the practical steps.
For insurance aspects of mould in a strata unit, see our mould insurance claim tips for NSW and mould and home insurance guides. Lot owners’ contents policies and owners corporation building policies interact in ways that are worth understanding before making a claim.
FAQs
How do I know if the mould source is common property or my lot?
Follow the water: where is it entering from? If it comes through an external wall, the roof, or from a building service like the main drain stack, it is most likely common property. If it comes from your own shower, your own plumbing, or your own ventilation behaviour, it is more likely your responsibility. When it is genuinely unclear, an independent inspection report identifying the source is the practical first step.
The owners corporation says the mould is my fault. What do I do?
Get an independent assessment of the source and document it fully. If you disagree with the owners corporation’s position, and the independent evidence supports your view, NCAT is the formal dispute resolution path for strata matters. A strata lawyer can advise on whether your case is strong before you proceed.
Can I fix the mould myself and claim the cost from the owners corporation?
In general, you should notify the owners corporation and give them the opportunity to arrange repair before taking unilateral action. Arranging your own repair and then seeking reimbursement can create complications. Get legal advice from a strata lawyer before spending money you intend to recover.
My bathroom exhaust fan vents into the roof void, not outside. Is that common property?
In most cases the venting system, including the path from the fan to the exterior, is common property even if the fan unit itself is within the lot. If it is venting into the common ceiling void and creating mould there, that is the owners corporation’s problem to address. Raise it in writing with the strata manager.
How long does the owners corporation have to respond to a mould report?
There is no single fixed timeframe in the legislation. “Reasonable time” depends on the urgency. Where mould poses an immediate habitability concern, the response should be faster. For ongoing disputes about maintenance backlogs, the strata committee and NCAT provide the resolution pathway.