An ice dam is a ridge of ice at the edge of a roof that stops meltwater draining. Water backs up behind it, sits on the roof, and eventually finds a way under the shingles and into the building.
People treat it as a roofing problem. It is almost always a heat-loss problem.
The mechanism
For an ice dam to form you need snow on the roof and a roof surface that is warm in the middle and cold at the edge.
Heat escaping from the house warms the underside of the roof deck over the heated part of the building. Snow sitting there melts, even when it is well below freezing outside. That meltwater runs down the slope until it reaches the eave - which overhangs unheated space and stays at outside temperature.
There it refreezes. Repeat this over days and the ice builds into a dam. Water then pools behind it, and pooled water on a shingle roof is not something the roof was designed for. Shingles shed water running downhill; they do not hold standing water.
The tell is simple: if you have icicles hanging off the eaves while it is cold out, heat is leaving your attic. Icicles are not decorative in Alberta - they are a diagnostic.
Why Alberta is a strong ice dam climate
The chinook belt in particular gives you exactly the conditions that build dams.
Steady deep cold produces less melt-freeze cycling. What produces ice dams is repeated crossing of freezing, and that is precisely what a chinook winter delivers - a warm spell melts accumulated snow, then the temperature drops sharply and refreezes it at the roof edge. Then it happens again.
Southern Alberta houses can therefore see significant ice damming even in a winter that is, on average, mild.
What does not fix it
Raking the roof removes the snow but not the heat loss. It is a temporary measure that has to be repeated after every snowfall, and it risks damaging the shingles.
Heat cables melt a channel through the dam. They manage the symptom, they use electricity all winter, and they do nothing about the heat you are losing - which is the same heat that was creating the dam.
More attic insulation, on its own, is closer but often disappointing. If warm air is leaking into the attic through gaps, adding depth on top does not stop the air; it just filters it. The attic still gets warm.
What does fix it
Stopping heat getting into the attic in the first place, in this order:
- Air seal the penetrations - the attic hatch, light fixtures, plumbing stacks, top plates, bathroom fan housings. This is where the warm air is going.
- Then insulate to depth, once the leaks are closed.
- Keep the eaves cold by not interrupting ventilation, so any snow at the edge stays frozen.
Sealing before insulating is the part people skip, and it is the part that decides whether the work succeeds.
If you already have water damage
Deal with the water first. Staining on a ceiling near an exterior wall in late winter is often an ice dam rather than a failed roof. Fixing the attic prevents the next one; it does not repair what has already happened.
Want the attic looked at properly? Get a quote.
Related: stopping attic heat loss in winter - attic spray foam - the attic hybrid system - high heating bills