A combination of snow accumulation, warm attic temperatures, and cold outside temperatures causes a freeze-thaw cycle.
Ice dams can become extremely heavy, tearing off gutters and loosening shingles. ICE DAMS
Preventing ice dams involves maintaining a cold roof by minimizing heat escape from the home. How to Prevent Ice Dams on Your Roof - Allstate A combination of snow accumulation, warm attic temperatures,
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. How to Prevent Ice Dams on Your Roof
Water trapped behind the ice dam backs up under shingles, causing leaks into the house, damaging insulation, walls, and ceilings.