Every winter in the Laurentides, homeowners notice thick ridges of ice forming along the edges of their roofs, often with long icicles hanging from the gutters. These ice dams may look picturesque, but they can cause serious damage: water infiltration, stained ceilings, wet insulation and even rot in the roof structure.
The good news is that ice dams are well understood and, in most cases, preventable. This guide explains why they form, how to recognize the warning signs and what you can do about them.
What is an ice dam?
An ice dam is a ridge of ice that forms at the lower edge of a sloped roof, usually above the eaves and gutters. It acts like a wall: melting snow from higher up on the roof flows down, hits the ice and has nowhere to go. The water then pools behind the dam and can work its way under the shingles and into the house.
Why do ice dams form?
Ice dams are caused by uneven roof temperatures. The process usually looks like this:
- Heat escapes from the living space into the attic.
- The warm attic heats the upper part of the roof deck.
- Snow on the warm part of the roof melts and the water runs down the slope.
- When the water reaches the eaves, which extend past the heated walls and stay cold, it freezes.
- Over days and weeks, the ice builds up into a dam.
In other words, an ice dam is usually a symptom of a heat problem in the attic, not simply a roofing problem. The long, cold winters and frequent freeze-thaw cycles in the Laurentides make the region especially prone to them.
The main contributing factors
Insufficient attic insulation
When insulation is too thin, compressed or poorly installed, heat from the house reaches the roof deck easily.
Air leaks into the attic
Warm, humid air can escape into the attic through gaps around light fixtures, ceiling hatches, plumbing stacks, chimneys and electrical wiring. Air leaks are often an even bigger contributor than a lack of insulation.
Poor attic ventilation
A well-ventilated attic keeps the roof deck cold and evenly cooled. Blocked soffit vents or a lack of ridge vents can trap warm air under the roof.
Roof design
Complex roofs with valleys, dormers and low slopes are more likely to collect snow and develop ice dams in certain spots.
Warning signs to watch for
- Thick ice along the eaves and large icicles hanging from the gutters
- Water stains or peeling paint on ceilings or exterior walls
- Damp or frosty insulation in the attic
- Water dripping inside window frames during mild spells
- Uneven snow melt on the roof, with bare patches near the top
If you see water inside, act quickly. Read our article Why Is My Roof Leaking? Common Causes Explained to understand other possible sources of leaks.
How to prevent ice dams
Long-term prevention focuses on keeping the roof deck cold and evenly cooled.
- Seal air leaks between the living space and the attic. This is often the most effective step.
- Add or upgrade attic insulation to reduce heat loss through the ceiling.
- Improve ventilation with clear soffit vents and adequate roof or ridge vents.
- Install a waterproof membrane along the eaves when the roof is replaced. This self-adhering underlayment protects the most vulnerable area of the roof from water backing up.
- Keep gutters clean in the fall so that meltwater can drain properly.
- Remove excess snow from the lower part of the roof after big storms, using a roof rake from the ground.
How to remove an ice dam safely
When an ice dam has already formed and water is getting inside, it is important to act carefully.
What you can do from the ground
Use a roof rake with a long handle to remove snow from the first few feet of the roof, working from the ground. This reduces the amount of meltwater feeding the dam. Never stand directly under the edge of the roof, as snow and ice can fall suddenly.
What to avoid
- Do not climb on an icy roof. Falls from roofs cause serious injuries every winter.
- Do not chip at the ice with an axe, hammer or shovel. You can easily break shingles and damage the gutters.
- Do not use open flames or torches to melt the ice.
- Do not spread rock salt directly on the roof, as it can damage roofing materials, metal and vegetation.
When to call a professional
If water is entering the house or the ice is thick, call a roofing professional. Roofers use specialized equipment, such as low-pressure steam, to remove ice without damaging the roof. A professional can also identify the underlying causes, such as ventilation or insulation problems.
Is it time for a roof replacement?
Repeated ice dams over the years can damage shingles, decking and flashing. If your roof is aging or shows several problems at once, read Roof Repair vs. Roof Replacement: When to Do Each and Signs Your Roof Is Failing.
When you are ready, you can request a roofing quote through the form on our homepage. Describe the problem, the age of your roof and any signs of water infiltration so a roofer can assess your situation accurately.
FAQ: ice dams on roofs
Are ice dams covered by home insurance?
Coverage depends on your policy. Sudden water damage caused by an ice dam may be covered, while damage resulting from lack of maintenance may not be. Read your policy carefully or ask your insurer.
Can heating cables prevent ice dams?
Heating cables installed along the eaves and in the gutters can help create channels for meltwater to drain. They treat the symptom, not the cause, so they work best combined with good insulation and ventilation.
Do metal roofs get ice dams?
Metal roofs shed snow more easily, which reduces the risk, but ice can still form if the attic is poorly insulated or ventilated. Snow sliding off a metal roof can also be dangerous, so snow guards are often recommended.
When is the best time to fix the causes of ice dams?
Attic insulation, air sealing and ventilation work is best done in summer or early fall, before the snow arrives. Roofing work can then be planned in good weather.
Is it safe to remove snow from my roof myself?
Using a roof rake from the ground is generally safe if you stay clear of falling snow. Climbing on a snowy or icy roof is dangerous and is best left to professionals with proper safety equipment.