Mould in rental properties is one of the most common and contentious issues in Australian tenancy law. Under the Residential Tenancies Acts of all states and territories, landlords must maintain properties in a reasonable state of repair and fit for habitation, while tenants must use the property in a reasonably clean manner and report maintenance issues promptly. When mould appears, determining responsibility depends on whether the cause is structural (landlord) or behavioural (tenant) — and independent professional assessment is often the only way to resolve this question objectively.

Australian Tenancy Law: The Legal Framework

Each Australian state and territory has its own Residential Tenancies Act, but the fundamental obligations regarding property condition are consistent across jurisdictions:

• NSW — Residential Tenancies Act 2010, s 63: landlord must provide and maintain premises in a reasonable state of repair, having regard to the age and condition of the premises at the start of the tenancy
• VIC — Residential Tenancies Act 1997, s 68: landlord must maintain the rented premises in good repair; the Rental Minimum Standards (2021) explicitly require properties to be free from mould caused by structural faults
• QLD — Residential Tenancies and Rooming Accommodation Act 2008, s 185: landlord must maintain premises in good repair and in a condition that is fit for the tenant to live in
• WA — Residential Tenancies Act 1987, s 42: premises must be in a reasonable state of cleanliness and repair at the start of the tenancy and maintained throughout
• SA — Residential Tenancies Act 1995, s 67: landlord must keep premises in a reasonable state of repair
• TAS, ACT, NT — comparable provisions exist in each jurisdiction’s tenancy legislation

Victoria’s 2021 Rental Minimum Standards are particularly noteworthy, explicitly stating that properties must be free from mould and damp caused by or related to the building structure. This codifies what other jurisdictions have established through tribunal case law: that structurally-caused mould is a landlord responsibility.

Landlord Obligations Regarding Mould

Landlords are responsible for mould that results from structural or building deficiencies, including:

Waterproofing failures: Leaking roofs, failed window seals, compromised bathroom waterproof membranes (especially in wet areas where the membrane has degraded — common in properties older than 15-20 years), and inadequate external drainage that directs water against the building.

Plumbing defects: Leaking pipes (including concealed pipes within wall cavities or under slabs), failed tapware, blocked or damaged stormwater drainage, and faulty hot water systems. Slow leaks in concealed plumbing can cause extensive hidden mould growth for months or years before becoming visible.

Inadequate ventilation: If the building design does not include adequate natural or mechanical ventilation — for example, bathrooms without windows or exhaust fans, bedrooms without openable windows, or enclosed laundries without ventilation — the resulting condensation and mould is a structural issue. The landlord cannot blame tenants for condensation mould in rooms that have no ventilation provision.

Subfloor moisture: Rising damp through concrete slabs without adequate damp-proof membranes, or subfloor moisture in raised-floor construction due to inadequate subfloor ventilation, are building defects. These issues are particularly common in older Australian homes and are entirely the landlord’s responsibility.

When mould is reported, landlords must respond within a reasonable timeframe. Urgent repairs (including water leaks that are causing ongoing damage) typically require response within 24-48 hours under most state tenancy laws. Non-urgent repairs must generally be addressed within 14-28 days of written notification.

Tenant Obligations and Responsibilities

Tenants also have obligations that, if breached, can shift mould responsibility to them:

Reasonable ventilation: Tenants should use exhaust fans in bathrooms and kitchens when bathing and cooking, open windows periodically to allow air circulation (when weather permits), and avoid blocking existing ventilation openings. However, this obligation is qualified — tenants are not expected to compensate for fundamentally inadequate building ventilation through extraordinary measures.

Reporting obligations: Tenants must report leaks, water damage, and mould growth to the landlord or property manager promptly. Failure to report a leaking tap for months, allowing mould to develop, may shift partial responsibility to the tenant for the mould (even though the tap itself remains the landlord’s maintenance responsibility). All reports should be in writing to create a documentary record.

Reasonable cleaning: Tenants are expected to maintain the property in a reasonably clean condition, which includes cleaning surface mould from bathroom tiles and other non-porous surfaces. Surface mould in a shower recess, for example, is a normal cleaning obligation comparable to removing soap scum.

Lifestyle factors: Drying large quantities of laundry indoors without ventilation, keeping windows permanently closed, blocking vents or exhaust fans, and overstocking rooms (reducing air circulation) can all contribute to condensation and mould. If the property has adequate ventilation provisions but the tenant’s use patterns create excessive moisture, the tenant may bear responsibility.

Determining Responsibility: The Role of Independent Assessment

In practice, most mould disputes involve contested causation — the landlord claims the tenant caused the mould through behaviour, while the tenant claims the building is deficient. This is where independent professional mould assessment becomes essential.

A professional assessment can determine the moisture source through systematic moisture mapping, identifying whether water is entering from external sources (landlord responsibility) or being generated internally through occupant activities (potentially tenant responsibility). Thermal imaging reveals hidden moisture pathways, rising damp, and thermal bridging that are structural in nature. Air sampling and surface sampling quantify the contamination and identify species, providing objective data that neither party can credibly dispute.

At Test Australia, our assessments for tenancy disputes are strictly independent. We are engaged by whichever party requests the assessment, but our findings are objective and evidence-based regardless of who is paying. We do not advocate for either party — we document facts and provide professional opinion on causation. This independence is critical for tribunal credibility, as assessments perceived as partisan are given less weight. Our reports are prepared to forensic standards suitable for presentation at NCAT, VCAT, QCAT, and equivalent tribunals in all Australian jurisdictions.

What Constitutes a Habitability Issue

Not all mould makes a property uninhabitable. Minor surface mould on bathroom tiles that can be cleaned through normal housekeeping does not constitute a habitability issue. However, a property may be considered unfit for habitation when:

• Mould contamination is extensive (affecting multiple rooms, large wall areas, or structural elements)
• Air sampling reveals elevated indoor spore concentrations exceeding 500-1,000 CFU/m³ above outdoor baselines
• Toxigenic species such as Stachybotrys chartarum or Aspergillus fumigatus are identified in significant quantities
• Occupants are experiencing documented health effects attributable to the mould exposure
• The moisture source is structural and cannot be remedied without major works
• Vulnerable occupants (children, elderly, immunocompromised) are present and exposed

If a property is found to be uninhabitable due to mould, tenants may be entitled to rent reduction, compensation for alternative accommodation costs, and in severe cases, lease termination without penalty. Landlords who fail to address habitability issues after proper notification face potential orders from tenancy tribunals including compliance orders, compensation awards, and penalty provisions.

Dispute Resolution: Tribunals and Formal Processes

When informal resolution fails, each state has a dedicated tenancy tribunal that handles mould disputes:

• NSW: NSW Civil and Administrative Tribunal (NCAT)
• VIC: Victorian Civil and Administrative Tribunal (VCAT)
• QLD: Queensland Civil and Administrative Tribunal (QCAT)
• WA: Magistrates Court (minor disputes)
• SA: South Australian Civil and Administrative Tribunal (SACAT)
• TAS: Residential Tenancy Commissioner
• ACT: ACT Civil and Administrative Tribunal (ACAT)
• NT: Northern Territory Civil and Administrative Tribunal (NTCAT)

In tribunal proceedings, independent professional evidence is given significant weight. A report from a qualified assessor documenting the extent of contamination, the moisture source, and the cause of the mould problem provides objective evidence that helps the tribunal determine responsibility. Without professional evidence, disputes often come down to one party’s word against the other — a situation that benefits neither side.

Whether you are a landlord wanting to establish that a tenant’s behaviour caused the mould, or a tenant wanting to demonstrate that structural defects are responsible, an independent assessment from a qualified professional provides the evidence you need. Test Australia provides forensic-standard assessments for tenancy disputes — contact us to discuss your situation.