Ice damming in winter is a ridge of frozen water that accumulates at a roof edge. This causes the snow-melt above it to dam. This water can leak through roof tiles and shingles because their lower edges do not shed water was well as their upper ones.

The water that falls past the tiles drips onto insulation and ceilings below. In a worst-case scenario, it could also damage internal walls, and floors. The first warnings are a damp, mouldy environment. However, if left unattended ice damming can lead to a hefty repair bill.

The Numbers Behind Ice Damming in Winter

Ice forms when the ambient temperature is below 32º F / 0º C for a sustained period. Conversely, ice and snow melts when the temperature is above that point. Ice damming in winter occurs when the temperature reaches freezing for a sustained period. If the snow does not freeze higher up the roof, that part is relatively warmer.

Ice damming starts at the lowest part of the roof, which extends beyond the outside walls. The relatively warmer part of the roof is above living space, from whence heat rises through conduction, convection, and radiation. This heat finds its way into roof space through gaps in the ceiling insulation.

Ice dams form from snow and ice melt higher up the roof. If we can prevent this happening, then the water can flow smoothly down the roof and over the eavestroughing. The solution is to draw cold outside air through soffit vents into unoccupied roof space, and then release it through roof vents into the atmosphere outside. This creates, renewable, natural ventilation.

A surprising number of buildings, particularly older homes in Calgary lack proper soffit and roof ventilation. While building specifications provide for high snow loads, the weight of ice damming in winter may exceed this provision. Moreover, it can permanently ruin the gutters on which it accumulates, and is hence something to avoid.

How Specialists Deal with Severe Ice Damming in Winter

Ice damming can be prevented by removing snow when it falls, using a roof rake and push broom. Where it has already formed – and the roof is leaking – channels may be formed using a hosepipe on a warm day, although this is only a stopgap solution.

For safety sake, we advise against homeowners climbing onto roofs. Valiant Exteriors Ltd. are masters in the field, and you will notice the difference when you call.