Ice dams are barriers to water runoff on the roof. They usually form at the roof edge, just above the gutter, in cold, snowy climates. They form when snow melting on warmer areas of the roof, usually near the ridge, runs down and refreezes at colder roof overhangs. Warm spots on the roof are caused by the heat that escapes from the living space into the attic. Once this cycle of melting and refreezing begins, a barrier is formed, trapping the snowmelt and allowing it to flow up and under shingles. As water begins to penetrate sheathing, insulation, wall cavities, and sheetrock or plaster:

• paint can begin peeling on both inside and outside walls
• roof coverings, fascia and gutters can be damaged
• structural damage can result from the weight of the ice dam

Homeowners usually blame their gutters, since that's where the problem appears to be. But newer, wider, deeper gutters won't solve the problem. Nor will additional layers of insulation alone. What will solve it is adequate ventilation combined with proper levels of insulation.