Concerned with mould in your attic?

March 22nd 2013
Concerned with mould in your attic?

You’re trying to sell your house and just discovered that there’s mould in your attic. Maybe it was the prospective buyer’s inspector that made the discovery. Now your deal is on the line and you’re in a panic.


Why does mould grow in the attic?


Mould doesn't grow withot moisture, There could be several causes of moisture in an attic. Bathroom or kitchen hood vents could be disconnected for some reason. Or worse, never connected in the first place. All the hot moist air has been dumping into the attic and condensing on the cooler attic sheathing and framing providing the optimal conditions for spores to grow and spread.  There could be an issue with inadequate roofing ventilation.. Anothoer souroce of moisture is a roof leak. If not caught quickly, roof leaks can rot the sheathing. Leaks will usually result in different fungal organisms that can affect the structure. If there is no vapour barrier between living and attic space, moisture created within the living space could be making its way into the attic area.


What’s the fix?


The cost to repair causes of moisture can be pretty straightfoward. Reconnect the vents and ensure they vent outside. Do NOT route the duct to the soffits as this is designed for air to enter the attic not exit it. If replacing the ducts use insulated ones so that condensation doesn’t take place in the duct and drip back onto your ceiling. Soffit baffles are very inexpensive but they are a pain to install. They should be spaced into every other space. Roofs should have 1 square foot of venting for every 200 square feet of roof surface. Proper venting of a roof cavity is best achieved is the radio of soffit venting and ridge venting is 50/50.


Building Science


Air moves from the occupied space and from the soffit venting INTO the attic by design. It does not move from the attic into the occupied space. This fact is poorly understood by most as it is thought that mould in the attic can present a health risk to the occupants. This is very unlikely. The air is designed to rise and exhaust out of the roof vents or ridge vents at the top of the attic. This means that as mould spores are released into the air, the majority are exhausted outside through the roof vents. There should be a vapour barrier (such as 6 mm poly) on the underside of the attic insulation. This will eliminate any moisture being transferred into the attic from living space, and vice versa.


What to do about the mould?


Now that you addressed your moisture issue, the mould will no longer grow, you can now deal with it. The big question many have is HOW to deal with it.  Let’s make one thing real clear. Remediation means complete removal of the mould. Any materials that are considered porous or semi-porous must be disposed of. This means all OSB sheathing and insulation MUST be replaced or it’s NOT remediation. Any treatment that claims to remediate and doesn’t remove the mould is based is not an accepted guideline in for mould remediation North America.


All encapsulants are white. When anyone sticks their head in the attic and sees white, there are only two possibilities – fire or mould. Neither is good and therefore it’s a big acknowledgement that there was a problem. This may result in a lower value for your home. Using encapsulants is not remediation either.


Most often, if mould is present in your attic, it is isolated in an area away from your living space (hot air rises), and an expensive remediation is not necessary.  If you could remove the visual staining then your problem is solved.  After researching the marketplace there are a few professional products that will treat wood surfaces and remove the staining caused by mould.  This is possible once it is determined that the mould is only a surface contamination and not rot.


The process is the following: the mould is HEPA vacuumed to remove the spores, then the wood stained surfaces are treated. The solution causes the staining to disappear almost 100%. This is not remediation but it does solve the problem for many attics.


If you are unsure, it is suggested to have your mould and moisture investigation by an experienced environmental consultant.