Ice dams
Why ice builds up at the eaves, how to stop it forming, and who clears it when it does.
How to stop ice dams
An ice dam is a ridge of ice along the eaves that holds meltwater on the roof. Heat escaping from the house melts the snow from below, the water refreezes at the cold overhang, and what backs up behind it can get under the shingles and into ceilings and walls. Dams are most common with snow on the roof and the outdoor temperature just below freezing (NDSU Extension).
Rake the lower roof from the ground
After each heavy snowfall, pull the snow off the lowest few feet above the eaves, where dams form. NDSU Extension advises a roof rake instead of climbing onto the roof.
Keep a drain path open, if you need one
Heat cable along the eaves and down the gutters melts a channel so water behind the dam can drain. NDSU Extension warns that it treats the symptom, not the cause.
Fix the cause in the attic
Seal the air leaks into the attic first, then add insulation and keep the vents clear, so the roof deck stays as cold as the air outside. In most homes this is a contractor’s job.
Safety: Stay off the roof and work from the ground. Keep yourself and the pole at least 3 m (10 ft) from overhead lines and clear of the service wires to the house, as Hydro-Québec advises. Roof heat cable plugs only into a grounded, ground-fault protected outdoor outlet (US CPSC).
What helps
A roof rake does the part that matters, from the ground. Heat cable makes most sense on a roof that dams in the same spots every year while you plan the attic work.
Roof rakes
Snow Joe Roofer Joe 21 ft Telescoping Roof Rake, Poly Blade
4.8 lb rake that reaches about 27 ft overhead from the ground
US retailers$58.47–$105.99at Target · prices may have changedPrice checked . Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Target at the time of purchase will apply to the purchase of this product.Check price at Target (opens in a new tab)$58.47–$105.99at Target · prices may have changedPrice checked . Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Target at the time of purchase will apply to the purchase of this product.Check price at Target (opens in a new tab)
Heat cables
Raychem FrostGuard 120 V Self-Regulating Heating Cable, 50 ft
Self-regulating plug-in cable approved for metal and shake roofs
Frost King Electric Roof Cable Kit, 60 ft
60 ft plug-in roof and gutter kit with clips and spacers in the box
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Our guide
Questions about ice dams
Does heat cable stop ice dams?
It keeps a channel open so water can drain past the dam, which can stop leaks, but it does not remove the cause: that takes air sealing, insulation and ventilation in the attic (NDSU Extension). The cable needs a ground-fault protected outdoor outlet and has to run down through the gutters and downspouts to work.
Can heat cable go on any roof?
No. Frost King’s roof cable instructions rule out wood shingles, rubber or membrane roofs, tar and gravel, flat roofs and wooden gutters. Raychem’s self-regulating FrostGuard is approved on more roof types, including metal (installation manual). Check the maker’s list for yours.
How much insulation stops ice dams?
NDSU Extension says attics in northern climates need about 15 inches of blown-in insulation, around R-50, though the right level depends on the type of insulation and your local code. Seal the air leaks first: new insulation laid on top buries the gaps.
Why does ice come back in the same spot?
That spot is losing heat. Look for a recessed light, bathroom fan, chimney or attic hatch below it, and start the air sealing there; NDSU Extension names these openings as where heat usually gets into the attic.
Should I climb on the roof to clear snow?
We don’t advise it. OSHA warns that snow hides skylights you can fall through and that a snow-loaded roof may not be safe to stand on. A rake from the ground does the job that matters for ice dams; for more, hire a professional.
Comes with
Snowstorms
Clearing heavy snow from the drive and the roof, and stopping ice dams.
Ice storms
Freezing rain, ice on lines, roofs and trees, and the long outages that follow.
Cold snaps
Safe heat, pipes that stay unfrozen and an alert before the house gets cold.