ICE DAMMING | Quebec | Isolation Eric Dutton in Quebec 450
January 28, 2016
An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow (water) from draining off the roof. The water that backs up behind the dam can leak into the home and cause damage to walls, ceilings, insulation, and other areas. how to stop icicles from forming on your roof
Ice dams form along the roof's edge, usually above the overhang. Heat and warm air leaking from the living space below melt the snow, which trickles down to the colder edge of the roof (above the eaves) and refreezes. Every inch of snow that accumulates on the roof insulates the roof deck a little more. This keeps more heat in the attic, which in turn makes the roof even warmer and melts more snow. Frigid outdoor temperatures ensure a fast and deep freeze at the eaves. The worst ice dams usually occur when a deep snow is followed by very cold weather.
Ice dams are caused by poor roof ventilation, lack of or improperly installed insulation and a warm attic space. Left untreated, ice dams can cause serious damage to your roof, gutters, paint, insulation, drywall, structure and even contribute to mold. Often the water that ice dams push into homes travels around wall and ceiling cavities, trapped by vapor barriers and other materials until it finds the path of least resistance to escape. By the time you see water inside, it’s usually been there for a while.
The way to stop ice dams from forming is to keep the entire roof cold. This means blocking all air leaks leading to the attic from the living space below, increasing the thickness of insulation on the attic floor, and installing a continuous soffit and ridge vent system to allow a continuous air flow.
Don't waste time or money placing electric heated cables on the shingles above the edge of the roof. They rarely, if ever, solve the problem. It takes a lot of electricity to prevent ice formation and the heating must begin before it gets cold enough for ice dams to form, not afterwards. Over time, the cables make shingles brittle. It's expensive to install and water can leak through the cable fasteners. Most often the cables create ice dams just above them.
When it comes to insulation, the more the better? Not always so. Improperly insulated homes are just as bad as under insulated homes when it comes to ice dams. We have fixed countless bad insulation jobs for this reason. Specifically, we frequently find insulation done in such a way as to inhibit proper ventilation. If you don’t address air leakage into the attic or rafter spaces, all the insulation in the world won’t prevent ice dams.