Ice dams: What are ice dams? How can they be avoided?
Ice dams are formed by continual thawing and refreezing of melting snow. Large masses of ice develop as snow on the upper part of the roof melts. The water runs under the snow and refreezes at the edge of the roof. Additional snow melts and forms pools against the dam gradually causing water to back up the roof often getting under the shingles and eventually leaking into the house.
- Poor or non existent vapour barrier which allows heat to escape into the attic.
- Air leakage through light fixtures, plumbing stacks, attic access hatches and fan vents etc.
- Insufficient attic insulation allowing warm air into the attic and melting the snow.
- Bright sunshine melting the snow;
- Naturally occurring ice accumulation due to various weather conditions.
How to avoid ice dams:
- Eliminate or reduce air leakage into the attic by installing a vapour barrier or sealing air leaks
- Lower the humidity level in the living space
- Have the snow removed from the roof
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