Here's how air leakage causes such serious problems: Warm air in the house rises through leaks in the ceiling and walls and enters the attic. As the warm damp air gets into the cooler attic during the winter, it condenses on the wooden beams. The wood expands. When the attic gets warm in spring and summer, the wood dries and contracts. This constant process can loosen nails and cause shingles to buckle.

1. Ice damming leads to serious damage. Melting snow on the roof re-freezes at roof edges and forms ice dams. These cause further melting snow to back up under shingles and enter the attic where it leads to moisture damage to ceilings and walls. Melting is caused by warm air rising from the interior of the house and also within poorly insulated and/or poorly sealed ducts located in the attic.

2. Mold is very unhealthy. It's associated with respiratory problems and allergies. Mold is something you don't find out about until you're thinking about a new roof -- after all, how many people ever go up in their attic?

3. Glass and mineral fiber insulation materials not only fail to solve these problems, they can actually make them worse. Some contractors will put in insulation plus ventilation with little thought to air leakage, moisture, condensation.

4. If you want to sell your house and the prospective buyer asks for a home inspection, you could be in for a major bill at a very inconvenient time!

What are the real causes and solutions? The traditional belief is that roof ventilation is a cure-all. It isn't. It can make the problem worse.

Here's why: Passive ventilation doesn't move much air through the attic. In winter, outside air has little ability to pick up moisture in an attic. Canadian Mortgage and Housing Corporation research shows this. Active ventilation tends to draw more warm moist air into the attic. This air may not leave the attic at all; it often stays behind and condenses on the wood -- leading to mildew, mold and rot.

How do you prevent these problems? Ensure that warmth and warm air containing moisture in the living space cannot get into the non-conditioned space in the attic. Keep the attic sealed off from the living area below (using air leakage control measures to seal holes, cracks, gaps). Not by adding insulation on its own.

Make sure that you talk to your roofing contractor. Get them to do a thorough investigation of your attic (and maybe walls) as well as your roof and advise you on the findings.

If you discover that there is a moisture buildup, you (or your roofer) can contact us at Zerodraft Calgary and we will make an appointment to visit. We can then work with that contractor as that is the best time to remedy these problems.