What is an Ice Dam?
An ice dam forms at a roof's edge when accumulated ice blocks the runoff from melting snow.
Definition
Purpose
The ice at the roof's edge may be a sign of heat escaping into the attic. Air leaks around ceiling openings and heat from ductwork can warm the roof enough to melt the snow above. Replacing damaged shingles may repair the immediate damage, but it won't keep another dam from forming if the heat loss continues.
Examples of Use
- Roof Inspections: Icicles may be the first visible clue. During a roof inspection, crews also check for ice collecting at the eaves or in roof valleys, damp areas in the attic, and water stains near exterior walls.
- Energy Audits: Auditors look for places where warm indoor air can escape into the attic. Gaps around attic hatches, light fittings, chimney penetrations, and exhaust fans are common areas to check.
- Reroofing: Crews fit protective underlayment at the eaves and joints where backed-up water could enter.
- Winter Repairs: Work may include drying or replacing wet insulation and repairing water-damaged finishes.
Notes
- When inspecting an ice dam, note how much snow has accumulated, where water is pooling, and whether there are leaks indoors. This can help identify where the snow is melting and freezing again.
- Preventing another ice dam means dealing with heat loss as well as the roof. Seal gaps that let warm air reach the attic and check whether more insulation is needed. On vented roofs, keep the soffit and ridge ventilation paths clear. Work near chimneys or hot equipment calls for materials rated for high temperatures.
- An ice-and-water membrane helps keep backed-up water out. It cannot stop the ice forming.
- A long-handled rake can clear lower-roof snow from the ground where access is safe, but careless use damages shingles. Leave established dams and unsafe removal work to a qualified contractor.
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