Ice dams: why they form and the damage they do inside

It’s February. You pull up to the cottage and a thick band of ice runs along the roof edge, with icicles down to the snowbank. Inside, a brown stain has appeared on the ceiling near the outside wall. That’s no coincidence: it’s an ice dam.

If you see an ice dam today

1. Look inside, under the dam

The dam is outside, but the damage is inside. Go upstairs and check the ceilings and the tops of the exterior walls on the side where the ice is thickest. Look for a new stain, blistering paint, a drip, a wet window frame. Check the window sills and around any skylights too.

2. Catch the water and move what you can

If water is dripping, put down a bucket, move furniture and boxes, roll up the rug. If water is running near a light fixture, an outlet or a ceiling fan, leave that circuit alone and call a master electrician.

3. Take photos before you touch anything

The dam seen from the ground, the icicles, the ceiling stain, the water. You’ll want these if you need to contact your insurer or broker.

4. Don’t chip the ice yourself

No axe, no hammer, no pick. You’ll damage the shingles, the metal or the eavestroughs, and you risk falling off an icy ladder or taking a block of ice on the head. Never climb onto an icy roof.

5. Pull snow off the edge — from the ground only

If the roof edge is within reach from the ground, a roof rake lets you pull down some of the snow above the dam. Less snow means less meltwater backing up behind the ice. Work from the side, never directly under the overhang.

6. Call a roofer for the rest

Removing an established dam and repairing shingles or the membrane is work for a roofer who holds a licence from the Régie du bâtiment du Québec. You can check the licence online in the RBQ registry.

Why it happens — especially at a Townships cottage

An ice dam is heat in the wrong place. Warm air from the house rises into the attic. If the insulation is thin or the attic is poorly ventilated, the roof deck warms up. Snow melts from underneath, water runs down toward the roof edge — and the edge, which overhangs the house, is cold. The water freezes again there. Day after day, the ridge of ice grows.

The water has to go somewhere. Behind the dam, meltwater pools. A shingled roof is built for water to run down, not to sit. The water works its way up under the shingles, finds the seams and nail holes, and gets into the attic.

The damage inside takes time to show. The water soaks the insulation first, which holds it. Then it runs along the rafters or into the top of the walls. The ceiling stain often appears only after days of leaking. Meanwhile, wet insulation insulates less — which warms the roof even more — and damp wood and drywall become good ground for mould.

Townships cottages stack the odds. Many cottages in Sutton, Brome Lake or Dunham were added onto or converted to four-season homes. Cathedral ceilings, hard-to-reach attics and lower roofs over additions are common. The mild spells followed by cold snaps that the region knows well melt and refreeze the snow several times in one winter. And keeping the heat on in an empty cottage produces exactly the warmth that melts the snow — with nobody looking at the roof.

Prevention: what you can do, and what belongs to a roofer

What an owner can do:

• Keep a roof rake and pull snow off the roof edge from the ground after big snowfalls.
• Clean the eavestroughs in the fall, so meltwater has a way out while it’s not freezing.
• Note where the dams form each winter: it’s often the same spot, above a source of heat.
• Make sure appliances that give off heat or moisture (dryer, bathroom fan) vent outdoors, not into the attic.
• Photograph the top-floor ceilings in the fall so you have something to compare against.

What belongs to an RBQ-licensed contractor:

• Assessing and improving attic insulation and ventilation.
• Sealing warm-air leaks into the attic (hatch, pot lights, ducts).
• Installing or redoing a waterproofing membrane along the eaves.
• Removing an ice dam and repairing the roofing.
• Installing heat cables along the eaves: the electrical work belongs to a master electrician.

In an empty house, how long before anyone notices?

In a lived-in house, someone eventually sees the drip or the stain. At an empty cottage, water gets into the insulation with no one around. The dam itself is visible from outside — but only if someone is there to look at the roof. If the next visit is three weeks away, the leak has three weeks to soak the insulation, the wood and the drywall.

Spotting the dam early means the snow can come off, or a roofer can come in, before water gets inside. If insurance comes into it, conditions vary from one insurer to the next: ask your broker what applies to water damage caused by ice.

What we look at on a visit

On every winter visit, we look from the ground at the snow and ice along the roof edge, the icicles and the eavestroughs, all the way around the house. Inside, we check the top-floor ceilings, around the chimney and skylights, the window sills, and we note any musty smell. Every finding is photographed and time-stamped in the report, so you can see a dam growing from one visit to the next.

If something’s off, we call you the same day, with photos. If needed, we meet an RBQ-licensed roofer on site and document the work.