How to prevent mould, ice and condensation
Q How do I stop ice from building up on the inside of my north-facing windows? This room is colder than the rest of house, and I have insulating the blinds pulled down most of the way at night to save energy. We had a heat recovery ven-tilator, but it’s broken now. Would replacing the HRV (heat recovery ventilation) help the windows? They were always wet and icy even when the old HRV was working.
A It sounds like your HRV was never working properly, since having it didn’t make a difference to window condensation. HRVs can make any house dry enough to prevent condensation completely on uncovered windows.
At least as important as dry windows is the way HRVs boost indoor air quality and health. Learn exactly how with my indoor air-quality video tutorial: stevemaxwell.ca/indoor-air.
Even with an HRV working properly, window condensation and icing can still happen when windows are mostly but not completely covered. Your blinds create a very cold micro climate around the glass, but if warm air from the room is allowed to enter this space it will lead to condensation. Proper insulating blinds are designed to seal around the edges to prevent this from happening.
All else being equal, the cooler the room temperature the more likely window condensation and icing is to occur. Increasing the temperature of your northfacing rooms will help solve the problem.
How can I stop mould grow Q ing in my attic and the ceiling It only happens in win below? ter, and the roof isn’t leaking.
A Moisture is always somewhere behind the growth of mould, no matter where it happens, and there are two main causes of wintertime moisture buildup.
In the case of your attic, moisture could be appearing on surfaces if warm, heated indoor air is leaking into the attic, causing condensation and liquid water that drips down to the ceiling from above.
Given the fact that mould is growing both in the attic and on the ceiling, air leakage is probably the cause.
The most common source of air leakage into Canadian attics is an improperly sealed attic hatch. Openings in the drywall and vapour barrier for ceiling lights are also a common source of this trouble.
Another dynamic is the way walls and ceilings can form condensation on interior surfaces if there isn’t enough insulation present behind them. If the drywall surface gets cold enough during winter, liquid water forms on the painted surface, leading to mould growth.
Sealing your attic access hatch to prevent the movement of indoor air past it is the first step. Adding more attic ventilation will also help, but that will have to wait until spring. While you’re up in the attic, look to see if there’s less insulation in places where ceiling mould happens, adding more if needed.
With moisture under control, kill mould wherever you see it. Bleach solutions are now discouraged by health and safety authorities, but non-bleach, non-toxic, registered mould products are available and effective.