April 4, 2026 · 9 min read
What is actually happening
Heat escapes from the house into the attic. It warms the underside of the roof deck and melts the snow sitting on it. That water runs down to the eave, which is cold because there is no heated space under it, and freezes there.
The ridge of ice grows, water pools behind it, and eventually finds its way under the shingles and into the ceiling. Shingles shed water running downhill; they are not designed to hold back a standing pool.
This is why ice dams show up on well-snowed roofs in mild winters more than in the deep cold. You need snow on the roof and a deck warm enough to melt it from below.
The clues before the damage
Look at your roof after a snowfall and compare it to the neighbours. Bare patches or early melt lines on your roof while theirs stays covered means heat is leaking out of yours.
A row of icicles along the eave, a thick ridge of ice at the gutter line, or ice building inside the trough are all later stages of the same thing.
Inside, watch for a stain appearing at the top of an exterior wall or in the corner of a ceiling during a thaw. That is meltwater, not a plumbing leak.
Chipping ice off is not a fix
Hacking at the ice damages shingles and the trough, and the dam forms again in a week. Salt tablets in a stocking will melt a channel but corrode metal and kill the plants below.
Steaming it off is fine as an emergency measure when water is already coming in. Low-pressure steam does not damage shingles the way a pressure washer or a hammer does. But it treats the symptom and the cause is still there in the attic.
The real fixes
Seal the attic bypasses first: pot lights, bathroom fans, the attic hatch, plumbing stacks, and the top plates of interior walls. This is where the warm air is actually getting through, and sealing it is usually cheaper than any of the other work.
Top up attic insulation so the attic stays cold. Older Edmonton homes often have six or eight inches where the current standard is far more. Make sure bathroom and kitchen fans vent all the way outside, not into the attic space.
Make sure soffit intake vents are open and not stuffed with insulation, so air can move from eave to ridge. Baffles hold insulation back at the eave so that path stays clear. Then keep the eavestrough clear so meltwater has somewhere to go.
What ice and water membrane does
When a roof is replaced, a self-adhering membrane goes along the eaves and in the valleys under the shingles. It seals around nails and holds back standing water where dams form.
It is not a licence to ignore the attic, but it means a dam that does form is far less likely to put water on your ceiling. If you are reroofing an older home that has had ice problems, ask how far up the slope that membrane runs.
If water is coming in now
Put a container under it, pull anything valuable away, and call. If the ceiling is bulging with trapped water, a small hole in the low point drains it in a controlled way instead of letting the whole sheet come down. This is what emergency roofing calls are for.
Do not go on an icy roof yourself. Every winter someone in this city gets badly hurt trying.