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.
