Every February, our phones fill with the same call: icicles the size of a forearm hanging from the eaves, a stain spreading across an upstairs ceiling, and a homeowner who has been told the roof needs replacing. Usually it does not. Ice dams are almost never a roofing problem. They are a heat problem that shows up on the roof.
What an ice dam actually is
Snow sits on the roof. Heat escaping from the house warms the roof deck from below and melts the underside of that snow. The meltwater runs down the slope under the snow blanket until it reaches the eave, which overhangs the house and is not heated. There it refreezes. Over days of Toronto's characteristic freeze-thaw cycling (the city sees roughly seventy days a year that cross 0 °C) the ice builds into a ridge. Water pooling behind the ridge has nowhere to go but up, under the slates, shingles or tiles, and into the house.
Three conditions are required: snow on the roof, a roof surface above 0 °C over the heated space, and an eave below 0 °C. Remove any one and the dam cannot form. You cannot control the snow. You can control the other two.
Why Toronto is ice dam country
- Freeze-thaw frequency. Toronto's winters hover around zero rather than staying deep-frozen. That is the ideal recipe for repeated melt-and-refreeze.
- Housing stock. Pre-war homes in Rosedale, the Annex, Forest Hill and the Beaches have plank roof decks, minimal insulation, and attics full of knee walls, dormers and chimney chases that leak warm air.
- Lake-effect snow. Heavier snowfall near the lake means a thicker insulating blanket on the roof, which keeps the deck warmer and melts more.
- Renovation. Pot lights, bathroom fans that vent into the attic and finished third floors have added heat to attics that were once cold.
The bandages: what does not fix it
Heat cable keeps a melt channel open so water can drain. It does nothing about the heat loss that created the dam, costs money to run, and often just moves the ice a foot further down the eavestrough. We install it, but only where geometry defeats the real fixes, and never as the primary solution.
Chipping ice off the roof destroys slate, cracks tile, tears shingles and voids warranties. Salt pucks corrode copper flashings and aluminum gutters and kill plantings below. If a dam must be removed in an emergency, low-pressure steam is the only method we use.
Replacing the roof without addressing the attic produces a beautiful new roof with the same ice dam the following winter.
The three permanent fixes
1. Air sealing
Warm air moving through gaps carries far more heat than conduction through insulation. Attic hatches, pot lights, plumbing and electrical penetrations, top plates and chimney chases are sealed with foam and fire-rated materials. This is the single highest-return step and the one most often skipped.
2. Insulation
Ontario's SB-12 standard calls for R-50 to R-60 in attics; many Toronto homes have R-20 or less. Topping up with blown cellulose or mineral wool, while keeping the eave baffles clear, keeps the roof deck close to outdoor temperature.
3. Ventilation
Balanced intake at the eaves and exhaust at the ridge flushes any remaining warm air before it can heat the deck. Ontario Building Code 9.19 sets a 1:300 minimum ratio; we design to it and confirm the airflow path is actually open, which in older homes it frequently is not.
The roofing layer's job is to make sure that when the fixes above are imperfect, water still cannot get in. We install high-temperature self-adhered ice-and-water membrane from the drip edge to at least 900 mm inside the warm wall line, on every roof, with copper eave flashings on slate and tile. It is the insurance policy, not the cure.
What to do this winter
- If water is entering the house, call us. We remove the dam with steam and stop the leak the same day.
- Photograph the icicles and any staining for your insurance file.
- Book an attic assessment for spring. It takes an hour, and it tells you exactly which of the three fixes your home needs.
- Do not let anyone chip, hammer or salt your roof.
Ice dams are solvable. In fifteen years we have never met one that survived proper air sealing, insulation and ventilation. The roof, more often than not, was fine all along.