Mould is arguably the most common environmental health hazard in residential properties, and almost entirely preventable with consistent moisture and ventilation management. The relationship is simpler than it looks: mould needs moisture, organic material, a suitable temperature, and stagnant air to establish — remove any one of those four and it doesn't get a foothold (see the Thermal Imaging & Moisture Diagnostics chapter for the full mechanism).
Key Principles
- Moisture control — the root variable; mould is the symptom, moisture is the cause
- Ventilation — moving air prevents the stagnant, humid microclimates mould needs
- Thermal stability (avoiding cold spots where condensation forms) — condensation occurs whenever a surface's temperature falls to or below the dew point of the surrounding air
- Humidity management
Daily Practices
- Ventilate bathrooms during and after use
- Use exhaust fans consistently, not just when visibly steamy — by the time steam is visible, humidity is already well above the level that matters
- Avoid drying clothes indoors — one of the single largest, most easily avoided humidity spikes in an ordinary home
- Reduce clutter that blocks airflow and traps moisture
- Clean regularly, particularly in bathrooms and kitchens
Red Flags
- Musty odours — often the earliest sign, before mould is visible
- Condensation on windows or cold surfaces
- Visible mould, even small patches
- Cold corners or cold external walls — exactly where thermal bridges push surface temperature down toward dew point
- Water staining on ceilings or walls
If you notice any red flags, address the moisture source directly rather than just cleaning the visible mould — it will return until the underlying cause (ventilation, insulation, a leak) is fixed. A cold corner that keeps growing mould no matter how often it's cleaned is very often a thermal bridge — invisible without a thermal camera, but simple to confirm once you know to look for it. See the IAQ Improvement Roadmap for the broader air-quality context.