Why do ice dams keep forming on my Calgary roof every February?

Ice dams form when heat escaping from your living space melts snow on your roof, and that meltwater refreezes at the cold eaves — and Calgary's February conditions are almost perfectly engineered to make this happen repeatedly.

The root cause is almost always an attic that's too warm. Heat rises through your ceiling, warms the attic space, and melts the snowpack sitting on your roof deck. That water runs down the slope toward the eaves, which extend beyond your exterior wall and sit over unheated space. The temperature drops sharply at the eaves, the water freezes, and a dam builds up. More meltwater backs up behind the dam, and that standing water finds its way under your shingles and into your home — staining ceilings, rotting sheathing, and damaging insulation.

February is the worst month for this in Calgary for a specific reason: you've had weeks of accumulated snowpack from December and January, and February often brings those classic chinook cycles where daytime temperatures swing above zero, then plunge back to -20°C overnight. That freeze-thaw cycling is brutal. Snow melts during a warm spell, partially drains, then refreezes hard against your eaves before it can fully clear. Repeat that cycle four or five times in a single month and you get a serious dam.

The Three Things Driving Your Problem

Attic insulation is usually the biggest culprit. The Alberta Building Code requires a minimum of R-40 in attic spaces for new construction, but many Calgary homes built in the 1970s and 1980s — particularly in communities like Dalhousie, Edgemont, and Woodbine — were built with R-20 or less. That's simply not enough to keep the heat in your living space and out of your attic. Adding blown-in cellulose or fiberglass to bring you up to R-50 or R-60 is one of the most cost-effective fixes you can make, and it may qualify for rebates under the Canada Greener Homes Grant (check nrcan.gc.ca for current eligibility).

Air sealing is often overlooked but matters just as much as insulation value. Warm air leaks through pot light housings, attic hatches, plumbing stacks, and any penetration in your ceiling. A poorly sealed attic hatch alone can dump enormous amounts of heat into your attic. Before adding insulation, a contractor should air-seal every penetration — otherwise you're insulating over a sieve.

Attic ventilation completes the picture. You need cold outside air circulating through your attic to keep the roof deck temperature close to the outdoor air temperature. Soffit vents bring cold air in; ridge vents or roof vents exhaust it. If your soffits are blocked with insulation, or your ridge vent is inadequate, the attic stays warm regardless of how much insulation you add.

What You Can Do Right Now

In the short term, a roof rake (a long-handled tool you use from the ground) to clear snow from the lower 4-6 feet of your roof after major snowfalls will reduce the fuel supply for ice dam formation. Do not go on your roof in winter — it's a serious fall hazard. Calcium chloride ice melt in a nylon stocking laid perpendicular across the dam can help open a drainage channel, but this is a band-aid, not a fix.

The real solution is getting a qualified insulation contractor into your attic to assess your current insulation levels, identify air leakage points, and check your ventilation. This is a one-time investment that pays back in lower heating bills, fewer ice dams, and a longer roof life. Typical attic insulation upgrades in Calgary run $2,500–$6,000 depending on attic size and access, and the energy savings alone often recover the cost within 5-7 years.

Browse insulation contractors in the Calgary Construction Network directory to find local professionals who know Calgary's climate and building stock.