5 Hidden Sources of Moisture in Homes (That Could Be Causing Mould)
If you’ve discovered mould growing in your home — or you’re constantly battling damp smells and condensation — the culprit could be moisture hiding in places you’d never think to check. While leaky pipes and roof damage are obvious causes, there are many subtle sources of water ingress that go unnoticed until mould takes hold.
Here are the 5 hidden sources of moisture we often find during inspections — and how to stop them before they lead to serious mould growth, property damage, and health risks.
1. Bathroom Exhaust Fans That Vent Into the Ceiling
Your bathroom might have a fan — but is it doing its job?
Many homes (especially older ones or poorly built new ones) have exhaust fans that vent directly into the ceiling voidrather than outside. This traps warm, moist air in an enclosed space — creating ideal conditions for hidden mould.
Solution: Ensure all exhaust fans are properly ducted to the exterior (e.g. roof vent or wall outlet), not just the roof cavity.
2. Built-In Wardrobes on External Walls
Wardrobes on external walls — especially those with poor insulation or south-facing orientation — are prime locations for condensation and mould.
When warm indoor air hits the cool surface of an external wall, moisture can condense behind the wardrobe. With limited ventilation and airflow, mould thrives unnoticed for months.
Solution: Improve insulation, add wardrobe ventilation gaps, and avoid packing clothes tightly against cold external walls.
3. Poorly Sealed Windows and Door Frames
Tiny gaps or cracks around windows and doors can allow wind-driven rain or moisture-laden air to seep in behind walls and under floors.
The problem is often invisible until you notice:
Bubbling paint
Musty smells
Warped skirting boards
Mould at the corners of windows
Solution: Use a moisture meter or thermal imaging to check for ingress, and re-seal or re-flash any compromised openings.
4. Concrete Slabs Without Proper Damp-Proof Membranes
Rising damp can occur when moisture from the ground wicks up through a concrete slab that lacks a functional damp-proof membrane (DPM). This is especially common in:
Older homes built before modern standards
Garage conversions
Poorly constructed extensions
Moisture can affect carpets, flooring, furniture, and wall linings — leading to persistent mould, especially around skirtings and corners.
Solution: Have your slab assessed. Moisture barriers, sealants, or under-slab ventilation may be required to address rising damp.
5. Internal Plumbing Leaks in Wall Cavities
Slow leaks from shower pipes, washing machines, dishwashers, or fridge water lines can drip inside wall cavities for months before signs appear.
By the time you see:
A musty smell
Stained or bulging walls
Visible mould patches
…the damage (and mould spread) may already be extensive.
Solution: A professional moisture inspection using thermal imaging or moisture sensors can identify hidden leaks early — before costly remediation is needed.
Why Hidden Moisture = Mould Risk
Mould only needs three things to grow:
Moisture
Organic material (like dust, timber, gyprock, carpet)
Time
Most homes already have the last two — so moisture is the trigger. And if that moisture is trapped behind walls or under floors, it becomes a breeding ground for harmful mould that affects both your property and your health.
How We Can Help
At Confluence Environmental, we specialise in identifying hidden sources of moisture and mould in homes across NSW — including the Central Coast, Newcastle, Hunter Valley, and Sydney.
Our moisture inspection services include:
Thermal imaging and moisture mapping
Visual and structural assessments
Mould and air quality testing
Detailed reporting and action plans
Independent, honest advice — no scare tactics
Suspect moisture or mould in your home?
Book a moisture inspection with Confluence Environmental today and get clear answers.
Call 0493 042 642 or book online for peace of mind.
Final Thoughts
Don’t wait for visible mould or a water stain to tell you something’s wrong. Hidden moisture is one of the most common — and preventable — causes of indoor mould in NSW homes.
If your property has musty odours, humidity issues, or recent water damage, get it checked early. At Confluence Environmental, we help you protect your health, your investment, and your peace of mind.