Why ice dams form
Heat escaping from the house warms the attic and the roof above it. Snow on the upper roof melts, runs down, and refreezes when it reaches the colder eaves, which sit out past the heated walls. Day after day the ridge of ice grows, and meltwater pools behind it. With nowhere to go, it backs up under the shingles and into the house.
It takes three things: snow on the roof, a warm attic, and cold eaves. Take away the warm attic and ice dams mostly stop.
Signs of ice dam roof damage
- Water stains on ceilings or walls near the outside of the house
- Peeling or bubbling paint and damp plaster in winter
- A thick ridge of ice at the gutters, and long icicles
- Wet or sagging soffits, and damp insulation in the attic
- Leaks that appear when it hasn't rained
What to do during a freeze
- Use a roof rake from the ground to clear the lower few feet of snow
- Don't chip at the ice, and don't climb onto an icy roof
- Catch any drips inside and keep clear of wet ceilings and light fixtures
- For a large ice dam, professional removal with low-pressure steam avoids damaging the shingles
How to prevent ice dams
Air sealing
Warm air leaks into the attic through gaps around light fixtures, pipes, chimneys and the attic hatch. Sealing those gaps is usually the biggest single fix.
Insulation
Enough insulation on the attic floor keeps the heat in the house, where it belongs.
Ventilation
Intake vents at the eaves and exhaust at the ridge help keep the roof deck cold. Baffles stop insulation blocking the eave vents.
Ice and water shield
When the roof is replaced, a self-sealing membrane along the eaves protects the house if water does back up. It's a standard part of a proper Michigan re-roof. See roof replacement.
Heat cables
They can keep channels open for meltwater, but they treat the symptom, not the cause.
Ice dams and your roof estimate
If you're replacing the roof, ask how the estimate handles ice and water shield and ventilation. If you're dealing with a leak now, the roof leak repair page explains what to do and what repairs typically cost.
Common questions
Are ice dams covered by homeowners insurance?
It depends on your policy. Water damage from an ice dam is often treated differently from the cost of fixing the underlying cause. Check your policy, and say in your request if it's an insurance claim.
Will heat cables stop ice dams?
Heat cables along the eaves can keep channels open for meltwater, but they manage the symptom rather than the cause. The lasting fix is keeping heat out of the attic.
Is it safe to remove an ice dam myself?
Clearing snow from the lower few feet of the roof with a roof rake, from the ground, is generally safe. Chipping at the ice, climbing a ladder onto an icy roof or using a hammer or pick is not, and it damages the shingles.
Will a new roof stop ice dams?
It helps: ice and water shield along the eaves protects the house if water backs up, and a re-roof is the right time to fix ventilation. But if the attic keeps losing heat, ice will still form.
When should I call a roofer?
If water is coming in, if the ice ridge keeps coming back every winter, or if you see stains near the outside walls. A roofer can check for damage and look at ventilation, and many work with insulation contractors on the attic side.
