Ice dams form when attic heat melts roof snow that refreezes at the eave. The resulting water backs under shingles and leaks into ceilings, walls, and insulation. Here's the cause, fix, and insurance picture.
Ice dams are caused by heat escaping from the living space into the attic, warming the roof deck and melting snow. The meltwater flows down the roof slope until it reaches the cold overhang (eave), where it refreezes into a ridge of ice — the dam. As the dam grows, it traps subsequent meltwater, which then backs up under shingles and eventually penetrates the roof deck, saturating attic insulation, ceiling drywall, and interior walls.
Ice dams occur most frequently in the Northeast, Great Lakes, upper Midwest, and Pacific Northwest — anywhere with freezing temperatures and significant snowfall. Homes most at risk: those with inadequate attic insulation (below R-38), poorly sealed attic bypasses (recessed lights, plumbing chases, attic hatches), and minimal eave ventilation. Cathedral ceilings and dormers are structurally prone to dam formation regardless of insulation quality.
The permanent solution addresses both heat and ventilation: seal all attic air leaks, upgrade attic insulation to R-49+, and ensure proper ridge and soffit ventilation to keep the roof deck uniformly cold. Heating cables are a maintenance tool, not a fix — they consume energy continuously and fail to address the underlying thermal issue. A properly insulated and ventilated attic will not form ice dams even in severe winters.
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