By Anne Patterson
Talk to just about any building contractor in the northern part of the country, and he's likely to tell you that ice damming is one of the biggest problems facing roofs in his area. Remodeler Mark Yandell of Yandell Construction Co., Lake Bluff, Ill., has had plenty of experience in preventing ice damming and correcting existing roofing problems. For the last 20 years he has been remodeling homes in northern Illinois, where there usually is snow from December through March.
Imperfect insulation and ventilation on the roof are the major causes of ice damming, Yandell says "If the roof insulation is inadequate, when a heavy snowfall accumulates on the roof, it will melt as the home's heat rises. However, it will freeze on the overhang beyond the plane of the outside wall, creating an ice 'dam' where the roof has remained cold. Water from melted snow can't go over the dam, so it backs up under the shingles into the building."
Most of the time trouble happens at the junction of the roof and the outside wall. You know there's a problem when you see water dripping down the windows. In homes with no overhang, water backs up under the roof. The worst problems occur when varying pitched roof planes come together to funnel a lot of drainage into a small area. Under these conditions, cracks are likely to form, causing water to leak into the home below.
Yandell offers several solutions to the problem of ice damming. Preventive measures work when the home receives a new roof. Another technique can usually correct an existing problem.
Apply an underlayment. Yandell suggests using an insulating underlayment product, adhering it directly to the roof's plywood surface. The underlayment creates a water tight barrier between the roof deck and shingles. "Overlap the fascia board with the membrane and overlap each three-foot-wide section of membrane." Yandell notes that the membrane seals around nail holes. One such product is Grace Ice & Water Shield; there are many similar products on the market today.
Provide adequate ventilation. If the budget and other considerations do not allow a new roof, it also may be possible to correct the ice damming by adding more ventilation. "You want to keep the whole roof cold in the winter," says Yandell. Good ventilation does that by dissipating the warm air in the attic, allowing snow to melt evenly so ice doesn't have a chance to build up.
The ideal distance between the ceiling and the insulation under the roof is 12 to 14 inches, according to Yandell. "To keep air moving, there needs to be venting in the roof and soffit. Most problems occur at the heel (end) of a rafter, where you need at least one inch of air space. You can request a rafter with an energy heel, which will provide more space for ventilation."
Retrofit by encapsulating insulation. You can stop an existing problem by covering the insulation with a sheathing board, Yandell advises. You also can accomplish encapsulation by covering the insulation with a tight fitting plastic.
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