How an ice dam causes water damage
An ice dam forms when heat escaping from the house melts snow on the upper roof. The meltwater runs down to the cold eave and refreezes into a ridge of ice. More meltwater pools behind that ridge, backs up under the shingles and leaks into the attic, ceilings and exterior walls.
Signs an ice dam is leaking inside
- Water stains along the top of exterior walls or at the ceiling edge
- Dripping around windows on the top floor
- Peeling paint near the ceiling line
- Icicles forming behind the gutter or coming through the soffit
- Wet or matted insulation at the attic edges
Why ice dam damage is easy to underestimate
The water enters at the eave, which sits directly above the exterior wall. It runs down inside that wall, soaking insulation from the top. The stain you see at the ceiling line may be the smallest part. The wall cavity below it can be wet all the way to the floor.
Ice dams also leak slowly and repeatedly. Each warm afternoon adds more water, and the wall never gets a chance to dry before the next thaw.
Roof leaks in other seasons
- Wind and hail from summer storms that lift or crack shingles
- Flashing failures around chimneys, vents and skylights
- Valleys where two roof planes meet
- Aging shingles near the end of their life
A roof leak can travel along a rafter or truss and show up several feet from where it entered.
What we do
- Check the attic. Wet insulation loses its insulating value and holds water against the ceiling. It is removed where saturated.
- Measure ceilings and walls to find how far water travelled.
- Open and dry affected cavities. See ceiling and wall water damage and structural drying.
- Protect contents and flooring below active drips.
- Document the interior damage.
What we do not do
Removing an ice dam from the roof and repairing shingles or flashing are jobs for a roofing contractor. Our work is the interior: drying and cleanup. Both are needed. If the leak is not stopped, the wall will get wet again.
Reducing ice dams
- Seal air leaks from the house into the attic: around light fixtures, vents and the attic hatch.
- Bring attic insulation up to current recommended levels.
- Keep soffit and ridge vents clear so the roof deck stays cold.
- Use a roof rake to pull snow off the lower few feet after heavy snowfall.
- Do not chip at the ice with tools. It damages shingles.
More in the ice dam water intrusion guide.