Signs of attic mould
Short answer: The most common signs of attic mould are grey-to-black staining on the underside of the roof sheathing (often worst on the north side), rusty or frosty nail tips, condensation or frost in cold weather, damp or compressed insulation, and a musty smell near the attic hatch. These usually point to warm, moist air from the house getting into the attic without enough ventilation.
What to look for
- Dark staining or blotches on the plywood or OSB roof sheathing
- Rusty, dripping or frosty nail tips
- Frost on the sheathing in cold weather, or water stains after it melts
- Damp, matted or discoloured insulation
- A musty smell in upstairs rooms or at the hatch
- Blocked soffit vents, or bathroom fans that vent into the attic instead of outside
Why attics get mouldy in BC
In the Lower Mainland's long, wet winters, warm house air carries moisture into the attic through gaps around lights, hatches and plumbing. It condenses on the cold roof deck. Blocked soffits, missing baffles and bathroom or kitchen fans that end in the attic make it worse. Many people first find out about attic mould at a home inspection during a sale.
What to do next
Don't disturb it yourself, especially in a home built before 1990, where asbestos testing comes first. Have it tested so you know what is there, then choose a treatment and fix the airflow. Compare our attic mould packages, from sealing to chemical wash, disinfection and airflow rebalancing.
Frequently asked questions
Is attic mould dangerous?
Attic mould can affect indoor air quality, and it shows there is a moisture problem that can damage the roof deck. Testing tells you how serious it is.
Will attic mould go away by itself?
No. Unless the moisture source and ventilation are fixed, it usually keeps growing in every wet season.
Can attic mould be found in a home inspection?
Yes. Inspectors often spot staining on the sheathing. Lab testing confirms whether it is mould.
Need help? We serve the Lower Mainland, Fraser Valley and beyond. Call 604-619-6655.