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Hidden Roof Leak Causes Mould Growth in Windsor Home | AAA Mould Removal
- Michael Nguyen
- Jun 17
- 6 min read
Hidden Roof Leak Causes Mould Growth in Windsor Home
By Michael Nguyen
Founder of AAA Mould Removal
Hidden mould growth often starts with one simple problem: moisture.
During a recent mould inspection in Windsor, our team investigated visible signs of water damage and a small amount of mould growth on the plaster ceiling in the lounge room, close to the chimney area. At first glance, the affected area appeared minor. However, once we entered the roof cavity, it became clear that the mould was being caused by a leak around the chimney.
Here is the youtube video you can watch the whole inspection process
Water had been entering the roof cavity, travelling down near the chimney, and dripping onto the upper side of the plaster ceiling. This created a damp surface where fungal growth could develop over time.
This case is a good reminder that mould is often not the main problem. It is usually a symptom of an underlying moisture issue.
Mould Inspection in Windsor: What We Found
The inspection began inside the lounge room, where there were signs of water damage on the plaster ceiling near the chimney.
The visible signs included:
Localised staining on the ceiling
Evidence of moisture impact
A small amount of mould growth
Damage located close to the chimney area
Because the staining and mould were located near a roof penetration, the next step was to inspect the roof cavity above the affected ceiling area.
This is an important part of a professional mould inspection. Surface mould can often be cleaned, but unless the source of moisture is identified and corrected, the mould may return.
For professional mould inspections in Sydney, visit:
Evidence of a Chimney Leak Inside the Roof Cavity
Inside the roof cavity, there was clear evidence that water had been leaking around the chimney area.
The leak appeared to be allowing water to drip down onto the upper side of the plasterboard ceiling. Over time, this repeated moisture exposure created the right conditions for mould growth on the plaster ceiling below.
This type of issue is common in older homes and properties with chimneys, roof penetrations, deteriorated flashing, cracked mortar, or poor sealing around the roof junction.
Even a small leak can create a significant mould problem if the material stays damp for long enough.
Why Roof Leaks Cause Mould Growth
Mould needs moisture to grow. When plasterboard, timber, insulation or ceiling materials become damp, mould spores can settle and begin to grow if the conditions remain suitable.
A roof leak can create mould growth because it may:
Wet the upper side of plasterboard ceilings
Affect insulation inside the roof cavity
Create damp timber surfaces
Increase humidity in enclosed roof spaces
Cause hidden moisture damage before symptoms appear indoors
In this Windsor home, the mould was not caused by poor cleaning or normal household dust. It was caused by a building moisture problem.
That is why proper inspection is so important.
Why Cleaning the Visible Mould Is Not Enough
One of the biggest mistakes homeowners make is cleaning visible mould without fixing the water source.
If the chimney leak remains active, moisture will continue to enter the roof cavity and affect the ceiling. This means the mould can return, even after cleaning.
Effective mould remediation should follow a proper sequence:
1. Identify the moisture source
2. Repair the leak or building defect
3. Dry the affected materials
4. Remove mould contamination safely
5. Verify that the area is dry and the mould issue has been resolved
At AAA Mould Removal, we focus on identifying the cause of mould growth, not just treating the visible surface.
For mould remediation and black mould removal services, visit:
Common Causes of Chimney-Related Roof Leaks
Chimneys are a common source of roof leaks because they create a penetration through the roof system. If the surrounding materials fail, water can enter the roof cavity.
Common causes include:
Failed chimney flashing
Cracked mortar or brickwork
Poor sealing around the chimney base
Deteriorated roof tiles or metal roofing
Blocked gutters causing water overflow
Previous repair work that was not properly sealed
These leaks are not always obvious from inside the living area. Sometimes the first visible sign is a ceiling stain, bubbling paint, musty odour, or mould growth.
Hidden Mould in Roof Cavities
Roof cavities are often overlooked because they are not part of the normal living space. However, they can still play a major role in indoor mould problems.
Mould inside a roof cavity can affect:
Plasterboard ceilings
Timber framing
Insulation
Stored items
Ceiling penetrations
Indoor air quality pathways
If there are gaps around downlights, vents, exhaust fans or ceiling penetrations, contaminants and odours may move between the roof cavity and occupied areas of the home.
This is why a complete mould inspection should include moisture investigation, roof cavity assessment where safe, and identification of the source of water intrusion.
Why Moisture Mapping Matters
Moisture mapping helps determine how far water damage has spread.
In a case like this, the visible mould may only appear in one small section of the ceiling, but moisture may have affected a larger hidden area above the plasterboard.
A proper assessment may include:
Visual inspection
Moisture readings
Thermal imaging where suitable
Roof cavity inspection
Checking surrounding building materials
Assessing whether insulation has been affected
This helps determine whether the issue is isolated or part of a wider moisture problem.
Our Scientific Approach to Mould Inspection
AAA Mould Removal is not just a cleaning company. We take a building science and moisture-focused approach to mould investigation and remediation.
Our inspections are designed to identify:
Why the mould is growing
Where the moisture is coming from
Which materials are affected
Whether hidden contamination may be present
What repairs are required before remediation
Whether mould removal or structural drying is needed
This approach helps prevent recurring mould problems and gives homeowners a clearer understanding of what is happening inside their property.
What Homeowners Should Do If They Notice Ceiling Mould
If you notice mould or staining on your ceiling, especially near a chimney, roof valley, bathroom exhaust, skylight or external wall, do not ignore it.
You should:
Avoid disturbing mouldy materials unnecessarily
Check whether the staining worsens after rain
Look for musty odours
Avoid painting over the affected area
Arrange a professional mould and moisture inspection
Repair the water source before cosmetic repairs
Painting over mould or water stains without fixing the cause may hide the problem temporarily, but it will not solve the underlying issue.
Mould Inspection and Remediation in Sydney
AAA Mould Removal provides professional mould inspection, mould testing, water damage assessment, structural drying and mould remediation services throughout Sydney.
We regularly investigate mould caused by:
Roof leaks
Chimney leaks
Plumbing leaks
Subfloor moisture
Condensation
Poor ventilation
Storm damage
Flooding and water ingress
If you suspect mould or water damage in your home, our team can help identify the cause and provide a practical remediation plan.
Book a professional mould inspection here:
Learn more about our mould removal process here:
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Frequently Asked Questions
Can a small roof leak cause mould?
Yes. Even a small roof leak can cause mould if it repeatedly wets plasterboard, timber or insulation. Mould does not need a major flood to grow. It only needs enough moisture and time.
Why is mould growing near my chimney?
Mould near a chimney is often linked to water intrusion around the chimney flashing, cracked mortar, damaged roof materials or poor sealing. A roof cavity inspection can help confirm the source.
Should I clean ceiling mould myself?
Small surface mould may sometimes be cleaned safely, but mould caused by a leak should be professionally assessed. If the water source is not repaired, the mould is likely to return.
Can mould grow on the back of plasterboard?
Yes. Plasterboard can support mould growth when it becomes damp. In roof leak situations, the upper side of the plasterboard ceiling may be affected before mould becomes visible inside the room.
Do I need to fix the roof before mould remediation?
Yes. The water source should be repaired before mould remediation. Otherwise, the affected materials may become wet again and mould may return.
Is roof cavity mould a health concern?
Mould in roof cavities may contribute to poor indoor air quality, especially if contaminants can move through ceiling gaps, vents, downlights or other openings. A professional assessment can help determine the level of concern.
About the Author
Michael Nguyen is the founder of AAA Mould Removal and a leading expert in mould remediation and building science.
Michael is IICRC Certified in Water Damage Restoration, Applied Microbial Remediation and Applied Structural Drying. He studied Microbiology at RMIT University, is a licensed builder and carpenter with a Diploma in Building & Construction, and is currently pursuing a double Bachelor’s degree in Medical Science and Environmental Science at Macquarie University.
Michael specialises in residential and commercial mould removal, black mould treatment, water damage restoration, structural drying and scientific mould investigation.
Contact AAA Mould Removal today for a comprehensive mould inspection.
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