Water trapped behind the ice dam backs up under shingles, causing leaks into the house, damaging insulation, walls, and ceilings.
Ice dams are a major cause of winter home damage, creating a thick ridge of ice at the edge of your roof that traps water, leading to roof leaks, damaged ceilings, and mold. They typically form when heat from the house escapes into the attic and melts snow on the upper roof, which then refreezes upon reaching the colder eaves, where the roof extends past the heated structure. ICE DAMS
A combination of snow accumulation, warm attic temperatures, and cold outside temperatures causes a freeze-thaw cycle. Water trapped behind the ice dam backs up