Ice dams: why they form and how to stop the leaks
Quick answer
An ice dam is a ridge of ice at the edge of the roof that traps melting snow and forces water back up under the shingles and into the house. The root cause is heat escaping into the attic, which melts snow that then refreezes at the cold eaves. Short term, rake snow off the lower roof and carefully melt drainage channels; the lasting fix is sealing attic air leaks and improving insulation and ventilation so the roof stays cold.
Common causes
- Warm attic air melting roof snow that refreezes at the colder eaves.
- Insufficient attic insulation and unsealed air leaks letting heat rise.
- Poor attic ventilation that keeps the roof deck warm.
- Clogged gutters and inadequate eave/ice-and-water protection.
What to check first
- Look for thick ice ridges and large icicles at the roof edge, plus any water stains on interior ceilings or walls.
- Safely rake snow off the lower roof edge from the ground after storms.
- Don't chip or hammer at the ice — you'll damage the shingles.
- Check attic insulation depth and feel for warm air leaks from the living space.
- Keep gutters clear in fall so meltwater can drain.
When it's urgent
Water actively leaking inside from an ice dam can ruin ceilings, insulation, and walls — deal with the interior leak and call a pro to remove the dam. Never climb an icy roof yourself, and watch for heavy icicles and ice that can fall on people below.
DIY vs. call a pro
You can likely DIY
- Raking snow off the lower roof from the ground.
- Improving attic insulation and air sealing over time.
- Keeping gutters clear and using calcium-chloride (not rock salt) to melt channels.
Call a pro for
- Steaming out an ice dam safely.
- Attic insulation and ventilation upgrades — the permanent fix.
- Roof and flashing repairs, and any winter roof work.
Estimated cost range
How HouseCue helps
HouseCue is a private, homeowner-first app that turns this from a one-time worry into a tracked plan. Snap a photo for an AI diagnosis, upload your inspection report to auto-build a handbook, and get seasonal reminders for your roof, HVAC, water heater, plumbing, and electrical — so nothing slips. Connecting with a pro is always optional and only when you choose.
Get started freeFrequently asked questions
What causes ice dams?
Heat escaping into the attic melts snow on the upper roof; the meltwater runs down to the cold eaves and refreezes into a dam. That dam then traps more meltwater, which backs up under the shingles and leaks inside. So ice dams are really an attic-heat and insulation problem.
How do I get rid of an ice dam?
Safely rake snow off the lower roof from the ground, and use calcium-chloride ice melt (in a sock laid across the dam) to open drainage channels — never chip at it or use rock salt. For a dam that's leaking inside, hire a pro to steam it off; don't climb an icy roof.
How do I prevent ice dams?
Keep the roof cold by sealing attic air leaks, adding insulation, and improving attic ventilation so heat doesn't melt the snow. Clearing gutters and raking the roof after big storms helps too, but the insulation-and-ventilation fix is what stops them long term.
Related guides
HouseCue guides are general educational information, not professional inspection, engineering, or contracting advice. Costs vary by market. For safety issues — gas, electrical, structural, or major water — contact a qualified professional.