Ice Dams 101: What Causes Them and What to Do

An ice dam is heat loss you can see. Warm air in the attic melts snow from underneath. The meltwater runs down to the eaves, which hang out past the warm part of the house and are cold, and freezes. Do that for a week and you have a ridge of ice at the roof edge, with a pond of meltwater backing up behind it and working under the shingles. That’s when the ceiling stains start.

Icicles are the tell. A few small ones are normal. Thick ones, or a solid bar of ice along the gutter line, mean a dam is forming.

If water is coming in right now

1. Move what you can out from under it and put a bucket down.
2. Take photos of the stain or drip. You may want them for insurance.
3. Keep people, pets and cars out from under the eaves. Ice lets go without warning.
4. Call us. Stay off the roof; a snowy roof with ice at the edge is the most dangerous surface on your property.

Don’t chip at it with a hammer or an axe, don’t pour salt or chemicals on it, and don’t run a hose at it. All of those damage the roof under the ice, and none of them fix the problem.

What we do

When it’s snowing and the dams are building, we go up. We clear the snow above the dam so it stops feeding, and cut the ice back without touching the shingles under it. If water’s been getting in, we look for where, and we can often tarp or patch the spot until the roof can be repaired in dry weather.

The fix that actually stops them

Removal handles this winter. Ice dams come back unless the heat loss is fixed, and that’s an attic problem, not a roof problem. The three usual causes: air leaking into the attic around lights, ducts and the attic hatch; not enough insulation, or insulation that’s been pushed around; and blocked or missing ventilation at the eaves and ridge. The Department of Energy’s explanation of air sealing and ventilation in cold climates is the clearest short read on why.

When we’re on the roof we can usually tell whether the ventilation is part of the problem. If it is, we’ll say so and quote the fix, so you’re not paying us to come back every February. If you get recurring dams on the same section of roof every year, that section is telling you something.

Read about roof snow and ice removal, or roof repair if the water already got in.