Ice dams form when heat escaping from your attic melts snow on the upper roof. That meltwater runs down to the colder eaves, refreezes, and builds a ridge of ice that traps more water behind it. Once the water has nowhere to go, it can back up under your shingles and into your attic, walls, or ceiling. St. Louis sees repeated freeze-thaw cycles rather than one long deep freeze, so this process can…
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