💧 Water & Weather
Ice Dams: Why They Form and How to Prevent Them
Those icicles along the eaves can push meltwater back under the roof. The real fix is in the attic.
Dana Whitlock · Sep 30, 2026 · 5 min read · 4 steps
An ice dam is a ridge of ice that forms along the lower edge of a roof. Snow higher up melts, runs down, and refreezes at the cold eaves. Water then pools behind the ridge and can work its way under shingles and into the walls or ceilings.
They are common in cold climates, and they are almost always a symptom of heat escaping into the roof space.
Why they form
For an ice dam to form, the upper part of the roof has to be above freezing while the eaves stay below. That happens when warm air from the house leaks into the attic and heats the roof deck. The overhanging eaves sit outside the heated area, so they stay cold.
Long-term prevention
- Seal air leaks from the house into the attic: around loft hatches, light fittings, pipes, and chimneys
- Bring attic insulation up to the recommended depth for your climate
- Make sure soffit and ridge vents are clear so cold air flows under the roof deck
- Keep bathroom and kitchen fans vented outside, not into the attic
Short-term measures
A roof rake with a long handle lets you pull snow off the lower few feet of the roof from the ground. Never climb onto an icy roof. Heated cables along the eaves can help in problem spots, but they treat the symptom and use electricity all winter.
If water is already coming in
Avoid chipping at the ice with tools — it is easy to damage shingles. A professional can steam the ice off safely. Inside, catch drips, move belongings, and photograph any damage for your insurer. After the thaw, check the attic for wet insulation, which loses its effectiveness and should be dried or replaced.
This is general home-maintenance information, not professional advice. Building codes, permits, and safe practices vary by location — consult a licensed contractor, electrician, or plumber for work beyond your experience.