Ontario winters are no joke—sub-zero temperatures, heavy snowfalls, and frequent freeze-thaw cycles are the perfect recipe for a common but serious roofing problem: ice dams. If left unchecked, ice dams can cause significant damage to your home, both inside and out.
In this guide, we’ll explain what ice dams are, why they happen, and—most importantly—how to prevent them on Ontario homes.
What Is an Ice Dam?
An ice dam is a ridge of ice that forms at the edge of a roof, usually at the eaves. It prevents melting snow from properly draining off the roof, which forces water to back up under your shingles and leak into your attic or home.
Why Ice Dams Are Common in Ontario
Ontario’s climate is a perfect storm for ice dam formation due to:
- Frequent temperature fluctuations (freeze during the night, thaw during the day)
- Heavy snow accumulation
- Poor attic insulation or ventilation
- Warm air leaks into the attic, heating the roof from underneath
As snow melts from the warmer sections of your roof, it runs down toward the colder eaves and re-freezes—creating an ice dam. This buildup can grow and trap even more water behind it.
Signs You Have an Ice Dam
- Large icicles hanging from the eaves or gutters
- Water leaking into ceilings or walls
- Wet or stained attic insulation
- Curling or buckling shingles near the roof edge
- Gutters filled with ice
If you notice these symptoms, you need to take action quickly to prevent costly damage.
7 Ice Dam Prevention Tips for Ontario Roofs
1. Improve Attic Insulation
- Keep warm air from escaping into the attic and warming your roof.
- Insulate attic floors to recommended R-values (R-50 or higher for Ontario).
2. Ventilate Your Attic Properly
- Cold attics are key to reducing uneven roof temperatures.
- Use ridge vents and soffit vents to create continuous airflow.
3. Seal Air Leaks
- Close gaps around light fixtures, chimneys, and attic hatches.
- Use spray foam or caulk to seal leaks that allow warm air into the attic.
4. Install Ice and Water Shield
- When reroofing, add this waterproof membrane under shingles at the eaves.
- It provides extra protection where ice dams are most likely to form.
5. Clean Gutters Before Winter
- Clogged gutters can worsen ice dams by trapping water.
- Ensure downspouts are clear and draining away from the house.
6. Use Snow Rakes After Heavy Snowfalls
- Remove snow from the bottom 3–4 feet of the roof after storms.
- Use a roof rake with a telescoping handle to do this safely from the ground.
7. Consider Heat Cables (as a last resort)
- Electric heat cables can melt ice along the eaves and gutters.
- Best used if other methods aren’t feasible due to roof design or budget.
What to Do If You Already Have an Ice Dam
Do NOT try to chip or hack at the ice. This can damage your shingles and lead to injury.
Instead:
- Use a calcium chloride ice melt product (not rock salt) in a sock or nylon stocking and place it across the dam.
- Call a professional roofer or ice dam removal service for safe steam removal if leaks are present.
Final Thoughts
Ice dams are a serious winter hazard for Ontario homeowners—but they’re also preventable. With the right combination of insulation, ventilation, and maintenance, you can keep your roof dry, your attic warm (but not too warm), and your home safe all winter long.
If your roof has recurring ice dam problems, it may be time to upgrade insulation, improve ventilation, or even consider a roof replacement designed for cold climates.