What is an ice dam?
Ice dams form when snow on warm patches of the roof repeatedly melt, flow downhill and freeze over the cold parts of the roof and gutters. Eventually a large mass of ice forms beneath the shingles or tiles. Water backs up behind these dams and sit in a big puddles on the roof, damaging it and causing leaks.
How can it be fixed?
The problem starts with uneven temperatures on the roof caused by heat loss from the buildings interior, a problem that may require extra insulation to solve. Gaps around plumbing vents and electrical wiring act like chimneys, siphoning heated interior air into the attic. A warm attic heats the roof, melting snow from the top of the roof down.
Spray-foam insulation is a simple and easy way to seal these gaps. Even if there are no gaps visible, additional insulation may be needed to prevent warm air from rising into the attic.
Specialty heat tapes are available to prevent ice build-up in gutters. If gutters fill with ice, they may start to sag from the weight and even break loose from their mountings. Heat tapes are a good idea for the roof, too. Low-temperature tapes provide constant heat to break the snowmelt and freeze cycles.