Mould Risk Management in Commercial Tenancies

Mould in commercial buildings is a business and compliance issue

Mould is a form of fungi that reproduces via airborne spores and can become a workplace health and safety hazard when it establishes indoors. In commercial tenancies, mould complaints are rarely “just maintenance”. They can disrupt operations, trigger insurance and fit-out disputes, affect occupant comfort, and escalate into formal complaints between landlords and tenants.

From an environmental risk perspective, mould also intersects with indoor air quality and building performance. The Australian Building Codes Board has published non-mandatory guidance to support understanding of the indoor air quality (IAQ) verification methods in the National Construction Code, which provide a framework for demonstrating indoor air quality performance in buildings.

As environmental consultants, we see the best outcomes when mould is managed like any other project risk: define the problem, collect defensible evidence, implement controls, and verify effectiveness.

Triggers and causes of mould in commercial buildings

Mould growth needs moisture, a suitable surface, and time. The practical takeaway is that controlling moisture is the only reliable way to prevent mould becoming established. In commercial tenancies, moisture sources are often hidden, intermittent, or distributed across base-building and tenancy systems.

Common moisture triggers in commercial tenancies

Typical triggers we investigate include:

• Roof leaks, flashing failures, gutter overflows and façade water ingress
• Plumbing leaks (including slow leaks within walls, risers, and amenities)
• HVAC issues such as condensate drainage problems or poorly managed humidity
• Poor ventilation in occupied areas and back-of-house spaces
• Flooding incidents, stormwater intrusion, and delayed drying after water damage
• Thermal bridging and localised condensation on cold surfaces

SafeWork NSW notes that mould spores are carried in the air and settle on surfaces; when conditions allow, mould can grow and create health and safety hazards at work.

Why “visible mould” is often the last symptom

In many tenancy disputes, the visible mould is treated as the problem, rather than a symptom of an underlying moisture pathway. This is where mould risk assessment becomes essential: surface cleaning without moisture control is unlikely to resolve recurrence, and it can weaken positions in landlord–tenant disputes because it doesn’t address causation.

Indoor air quality considerations

Mould complaints commonly come with IAQ concerns (odour, irritation, perceived “stale air”). Ventilation plays a key role in managing indoor air hazards; SafeWork NSW provides guidance on ventilation and emphasises WHS obligations to manage risks in workplaces.

IAQ assessment should be targeted and proportionate: the aim is to inform risk controls and verify outcomes, not to “test our way out” of a moisture issue.

Responsibility split in commercial leases

One of the fastest ways mould issues escalate is when responsibility is assumed rather than evidenced.

In NSW, guidance for retail and commercial leasing notes that tenants are generally responsible for non-structural repairs, while landlords are generally responsible for structural repairs, but obligations ultimately depend on the lease terms. That “depends on the lease” point is critical: commercial lease arrangements vary widely (including make-good clauses, outgoings, repair schedules, base-building vs tenancy services, and fit-out responsibilities).

Practical way to think about responsibility

An evidence-based approach usually starts with mapping the issue to likely control points:

• Base-building / structural pathways (roof, façade, slab, waterproofing, risers, common services) often sit with the landlord or building owner, subject to lease terms.
• Tenancy conditions and behaviours (blocking vents, unreported spills, process moisture generation, internal plumbing) may be within tenant control, again subject to lease terms and building rules.
• Workplace safety obligations can apply to whoever is the PCBU for the workplace, with duties to provide a work environment without risks to health and safety so far as reasonably practicable, supported by SafeWork NSW guidance and codes of practice.

Where disputes arise, the quality of the evidence about causation and risk is often what drives resolution speed—not the volume of correspondence.

Evidence-based resolution pathway

When mould disputes landlord tenant issues develop, our focus is to help clients move from allegation to verification. That means establishing a clear chain from cause → impact → controls → confirmation.

Step 1: define the problem and stabilise risk

Before detailed diagnostics, we typically recommend immediate, practical controls where people may be exposed:

• Isolate affected areas where feasible
• Address active leaks or water sources promptly
• Improve ventilation where it can be done safely and appropriately (without spreading contaminants)
• Implement housekeeping controls to prevent further moisture loading

This aligns with WHS expectations around managing workplace risks and maintaining work environments and facilities.

Step 2: conduct a mould risk assessment Australia stakeholders can rely on

A defensible mould risk assessment usually includes:

• Visual inspection and building history review (water events, maintenance logs, HVAC servicing)
• Moisture investigation (moisture meter readings, thermal imaging where appropriate, condensation assessment)
• Identification of building materials and susceptibility (porous vs non-porous, hidden cavities, flooring systems)
• Ventilation and humidity considerations (particularly where HVAC is implicated)
• Photographic documentation and annotated plans (location, extent, likely pathways)

Public health guidance recognises mould can grow on many building materials and in HVAC systems and can cause odour and damage, reinforcing why the investigation must consider systems, not just surfaces.

Step 3: fix moisture pathways first, then remediate

Effective remediation sequencing is non-negotiable:

• Rectify moisture drivers (leaks, drainage, condensate, humidity control, ventilation deficiencies)
• Remove or treat impacted materials where necessary, based on extent and material type
• Clean and decontaminate using methods suited to the substrate and risk profile
• Dry and verify (moisture targets, visual confirmation, and fit-for-occupation checks)

This approach reduces recurrence risk and creates a clearer evidentiary basis if responsibility is contested.

Step 4: document outcomes for disputes, insurers and asset managers

Evidence-based resolution is also “dispute-ready” resolution. Good documentation typically includes:

• A clear causation narrative supported by findings (not assumptions)
• Records of moisture readings and repairs completed
• Remediation scope, methodology and verification
• Recommendations for prevention (maintenance, ventilation management, tenant guidance)

For many commercial clients, this documentation becomes as important as the physical rectification because it supports governance, stakeholder communication, and future leasing decisions.

Reduce disruption by treating mould like a project risk

Mould in commercial buildings is best managed early, objectively, and with evidence. When the moisture trigger is identified and controlled, responsibilities are clarified under the lease, and the resolution pathway is properly documented, landlord–tenant disputes are far less likely to escalate.

If you’re dealing with recurring mould, persistent odours, or an emerging dispute in a NSW commercial tenancy, we can help you move quickly from uncertainty to a clear, defensible action plan.

How we can help

• Assess and test: We identify mould and moisture issues using air and surface sampling, moisture meters and thermal imaging to confirm the extent and likely drivers.
• Remediate safely: We remove mould and treat affected areas using industry-approved, environmentally responsible methods to restore healthy indoor environments.
• Verify the outcome: Post-remediation inspections and testing provide confidence that mould has been addressed and the risk of recurrence is reduced.

Next step: Learn more about our mould assessment and remediation services, or book a consultation to scope an evidence-based plan for your commercial property.