Climate Guide · 6 NE states
An ice dam looks like an eave problem. It’s almost always an attic problem. Understanding why is the difference between an expensive seasonal pattern of leaks and a permanent fix.
Snow accumulates on a roof. Heat from the conditioned space below escapes upward through the ceiling, into the attic, through the roof deck, and warms the snow on the upper roof. That snow melts. Meltwater runs down the roof until it reaches the cold overhang — the part of the roof that hangs out past the heated wall below it. The water hits the cold overhang and refreezes. A ridge of ice builds at the eave. New meltwater hits the ridge, has nowhere to go, and pushes back up under the shingles. That’s an ice dam.
Most roofers respond to an ice-dam leak by replacing the affected shingles and adding more ice-and-water shield. Sometimes they install heat cables. None of these fix the underlying cause — heat escaping into the attic. Next winter, with the same conditions, water finds a new path. The cycle continues until the homeowner realizes they’re paying for the same repair every February.
1. Air-seal attic penetrations (top plates, light fixtures, plumbing, attic hatch). This is the cheapest and most effective remediation. 2. Add insulation to R-49 minimum, properly distributed. 3. Verify balanced ventilation — soffit intake must equal ridge exhaust. 4. Retrofit ice-and-water shield 36-inches minimum from eave when re-roofing. 5. Install heat cables — only as targeted backup for cathedral-ceiling sections where 1–4 aren’t feasible.
If your attic has a cathedral-ceiling section (no attic above the living space — the underside of the roof is the ceiling), traditional attic remediation isn’t possible. Cathedral sections need closed-cell spray foam against the deck, very high R-value, and often heat cables as well. Talk to a roofer who’s done this work before — generic asphalt installers usually haven’t.
If you’re seeing an ice dam right now: don’t chip at it with a hammer (you’ll wreck the shingles), don’t pour rock salt on it (the chloride damages the asphalt). Call a roofing contractor with steam dam-removal equipment. Steam lifts the ice off without damage. Permanent attic remediation gets scheduled for spring.
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