Tenants experiencing chronic respiratory symptoms blamed mould from building defects. The landlord insisted the tenants caused the problem through poor ventilation habits. With tribunal proceedings imminent, our independent assessment uncovered the real cause: a bathroom exhaust fan ducted into the roof space and a broken subfloor downpipe — building defects that no amount of tenant ventilation could overcome.

The Situation

A family renting a 1990s brick home in Newcastle had been experiencing persistent health issues for over eight months — the mother and two children suffered chronic cough, nasal congestion, and aggravated asthma symptoms. Visible mould had appeared on bedroom ceilings, bathroom walls, and inside built-in wardrobes. The tenants had documented the mould with photographs and submitted three formal maintenance requests to the property manager over a six-month period.

The landlord’s response, through the property manager, was that the mould was caused by the tenants’ “lifestyle” — specifically, insufficient ventilation and drying clothes indoors. The landlord arranged for a cleaner to wipe mould from visible surfaces twice, but the mould returned within weeks each time. When the tenants escalated to the NSW Civil and Administrative Tribunal (NCAT) seeking a rent reduction and remediation order, the landlord counter-claimed that the tenants had caused the damage through their own behaviour.

Both parties needed objective evidence. The tenants’ solicitor engaged Test Australia to conduct an independent mould assessment that could determine the root cause and withstand scrutiny at tribunal.

Our Investigation

Our principal chemist conducted a comprehensive multi-method assessment designed to answer one critical question: Is the mould caused by building defects or occupant behaviour? The investigation included four complementary assessment methods:

Visual Inspection and Documentation

A thorough room-by-room inspection documented visible mould growth locations, extent, and species characteristics (colour, texture, pattern). We noted mould on bathroom ceiling and walls, two bedroom ceilings, inside all three bedroom wardrobes, and on the laundry wall behind the washing machine. The growth patterns were consistent with sustained moisture exposure rather than condensation from occasional tenant activities.

Moisture Mapping

Using thermal imaging (FLIR camera) and a calibrated pin moisture meter, we mapped moisture levels throughout the property. Thermal imaging reveals moisture hidden behind wall surfaces by detecting temperature differentials caused by evaporative cooling. Pin moisture meters provide precise readings of material moisture content at specific locations. We documented moisture readings at over 40 points across the property.

Air Sampling (Viable Spore Counts)

We collected indoor air samples from four locations (master bedroom, second bedroom, bathroom, living room) plus an outdoor control sample using calibrated air sampling pumps. Samples were submitted to an independent NATA-accredited laboratory for viable spore count analysis, which cultures and identifies the specific mould species present and their concentrations in colony-forming units per cubic metre (CFU/m³).

Surface Sampling

We collected 6 surface samples using tape lifts and swabs from visible mould growth locations for species identification. This confirmed whether the mould species present were consistent with chronic moisture exposure (e.g., Aspergillus, Penicillium, Stachybotrys) versus species associated with temporary condensation events.

What the Results Revealed

The results provided a clear, objective picture of the mould problem and its cause:

Air Quality Results

Indoor air sampling revealed significantly elevated spore counts:

• Master bedroom: 2,100 CFU/m³ (predominantly Aspergillus and Penicillium species)
• Second bedroom: 1,850 CFU/m³
• Bathroom: 3,200 CFU/m³
• Living room: 920 CFU/m³
• Outdoor control: 350 CFU/m³

Indoor-to-outdoor ratios of 2.6x to 9.1x confirmed an active indoor mould source. A ratio above 1.5x indicates an indoor source contributing to the spore load. The dominant species — Aspergillus niger, Aspergillus fumigatus, and Penicillium chrysogenum — are associated with chronic moisture conditions and are classified as potentially allergenic and irritant species with known health effects.

The Root Cause: Two Building Defects

Our moisture mapping and physical inspection identified two critical building defects that were directly causing the mould problem:

Defect 1: Bathroom exhaust fan ducted into roof space. The bathroom exhaust fan — which the tenants used regularly during showers — was ducted into the roof cavity rather than to the exterior of the building. This meant every shower pumped warm, moisture-laden air directly into the roof space, where it condensed on the underside of the roof sheeting and dripped onto ceiling insulation and plasterboard. Thermal imaging clearly showed moisture saturation in the ceiling above the bathroom and extending into adjacent bedroom ceilings. Pin moisture readings in the bathroom ceiling plasterboard were 28% — well above the 15% threshold that supports mould growth.

Defect 2: Broken downpipe at subfloor level. A stormwater downpipe at the rear of the property had separated from its connection at subfloor level, directing rainwater under the house rather than to the stormwater drain. Subfloor moisture readings were 22% (above the 15% threshold), and the subfloor ventilation was inadequate — several vents were blocked by garden beds built up against the external walls. The combination of water ingress and poor ventilation created chronic subfloor moisture that wicked up through the brick walls via capillary action, manifesting as the mould growth in ground-floor wardrobes and the laundry wall.

Ruling Out Tenant Behaviour

Our assessment specifically addressed the landlord’s claim that tenant behaviour was the cause. The evidence showed:

• The tenants were using the bathroom exhaust fan — but its ducting defect meant this actually worsened the problem by pumping moisture into the roof space
• No evidence of clothes drying indoors was observed during the inspection
• The mould distribution pattern (ceiling-down in bedrooms, wall-up from subfloor in wardrobes and laundry) was inconsistent with condensation from occupant activities and consistent with building-defect moisture sources
• Even perfect tenant ventilation behaviour could not overcome the two structural moisture sources identified

The Outcome

Our forensic report was submitted as expert evidence at NCAT. The tribunal accepted the findings and ruled in favour of the tenants. The orders required the landlord to:

1. Re-duct the bathroom exhaust fan to discharge to the exterior of the building within 14 days
2. Repair the broken downpipe and restore subfloor drainage within 14 days
3. Clear blocked subfloor vents and restore adequate subfloor ventilation
4. Engage a professional mould remediation contractor to remediate all affected areas, with post-remediation verification sampling to confirm clearance
5. Compensate the tenants with a rent reduction for the period of reduced habitability

The total remediation and repair cost to the landlord exceeded $15,000, plus the rent compensation. Had the building defects been addressed when the tenants first reported the issue, the cost would have been a fraction of this amount. The mould remediation alone — which would not have been needed if the defects were fixed promptly — accounted for $8,000 of the total.

Key Lessons

1. Independent, scientific assessment resolves “he-said-she-said” disputes with objective data. Both parties in this dispute had legitimate-sounding arguments. Only forensic assessment with air sampling, moisture mapping, and species identification could objectively determine the cause.
2. Mould is a symptom, not a cause. Wiping mould off surfaces treats the symptom but does nothing to address the underlying moisture source. Without identifying and eliminating the moisture source, mould will always return.
3. Building defects can be hidden in plain sight. The bathroom exhaust fan appeared to function normally — it turned on, it extracted air. Only investigation of the ducting revealed it was pumping moisture into the roof space. The broken downpipe was at subfloor level, invisible without specific inspection.
4. Elevated indoor spore counts confirm health risks. Air sampling results of 2,100-3,200 CFU/m³ against an outdoor baseline of 350 CFU/m³ provided objective evidence that the indoor environment posed a health risk — supporting the tenants’ health complaints with scientific data.
5. Early action saves money. The landlord could have fixed the exhaust fan ducting ($300-500) and the downpipe ($200-400) when the issue was first reported. Instead, months of delay resulted in extensive mould growth requiring $8,000 in remediation, plus tribunal costs, rent compensation, and professional assessment fees.

If you are involved in a mould dispute — whether as a tenant, landlord, or property manager — contact Test Australia for independent, objective mould assessment that provides the evidence needed to resolve the dispute.