Glossary
Ice dam
A ridge of ice forming at a roof edge when meltwater from a warmer upper roof refreezes over the unheated overhang, trapping water behind it.
The trapped water can back up under shingles and enter the building, typically appearing at the top of exterior walls or in ceilings near the perimeter.
Calgary's chinook cycling makes ice damming more pronounced than in steadily cold climates, because dams build and rebuild repeatedly through a single winter.
The underlying cause is heat escaping into the attic, so insulation and ventilation are the real fix rather than removing the ice.
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