How an ice dam forms
- Warm air leaks from the house into the attic and warms the roof deck.
- Snow on the upper roof melts and runs down.
- The eave overhangs the outside wall and stays cold, so the water refreezes there.
- Ice builds into a ridge. Meltwater pools behind it and works under the shingles.
Where the water goes
It enters at the roof edge, wets the attic insulation above the exterior wall, then runs down inside the wall cavity. Stains appear at the ceiling line and around window heads. The wall below can be wet without any visible sign.
During an active leak
- Catch drips and move belongings.
- From the ground, use a roof rake to pull snow off the lower three to four feet of roof.
- Do not climb on an icy roof or chip at the ice.
- Contact a roofing contractor about safe ice dam removal.
- Photograph the ice outside and the damage inside.
Preventing ice dams
| Fix | What it does |
|---|---|
| Air sealing | Stops warm air reaching the attic. The most effective step. |
| More attic insulation | Keeps heat in the house and the roof deck cold |
| Ventilation | Soffit and ridge vents carry away what heat does escape |
| Roof raking | Removes the snow that feeds the dam |
After the leak
Wet insulation and wall cavities need to be opened and dried, even if the stain looks minor. See ice dam and roof leak water damage.