Ice Dams

Ice dams are a familiar sight in Ontario during the winter. It’s common to see large, dangerous looking icicles hanging from the edges of roofs, and a heavy build up of ice in eaves troughs and gutters.

These ice dams form when two conditions combine: heavy snowfall and improper attic ventilation and insulation.

As temperatures change, that snow melts and begins to run off the roof, but then it refreezes at the roof’s edge, where temperatures tend to be lower. This process of melting and refreezing creates ice dams.

Did you know?

Believe it or not, ice dams can put as much as a thousand pounds of pressure per 100 square feet on your roof. This pressure can threaten the entire structural integrity of your home.

When it comes to ice dams, sometimes the ice you can’t see will cause the most damage. Ice dams often damage shingles, by creating water migration pathways through the roof system. Once these pathways are established, wind-driven rains or future ice dams can wreck havoc on your home.

When the temperature warms, this ice can travel these pathways between the exterior walls or even into your attic. This in turn can cause mold and wood rot, and damage your insulation, thus compounding the problem.

Ice dams can be caused by inadequate insulation or air leaks in the attic from improperly sealed attic penetrations.

Inadequate ventilation – leading to either heat build up or heat loss from the house to the attic -- is another major cause of ice dams.

Signs of Ice Damming Problem

  • • you notice ice dams on your roof, but not your neighbours'
  • • a persistent musty smell
  • • rusty nails on the underside of the roof sheathing
  • • cracked drywall and plaster
  • • frost build up on the underside of the roof sheathing

Ice dams can be prevented by sealing air leakage from the interior living space into the attic, improving attic insulation and proper roof ventilation systems. These warm air leaks, also known as “bypasses,” usually occur around vent pipes, exhaust fans, chimneys, attic hatches, wall and ceiling framing joints, wiring and lighting fixtures.

Remember: once the snow and ice has melted and the leak has stopped, it doesn’t mean your ice dam problem has gone away. Often leaks go undetected and travel between the walls, damaging insulation and the building structure.

Tips for preventing ice dams

  • • Improve ventilation
  • • Air seal attic penetrations
  • • Keep gutters and downspouts clear of leaves and other debris
  • • Wrap or insulate heating duct work, to reduce heat loss through your attic
  • • DO NOT use ice picks and other sharp tools on downspouts and gutters
  • • Improve insulation
  • • Waterproof your shingle underlayment with a product like CertainTeed WinterGuard

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