A winter problem common in Canadian homes: heat leaking into a poorly air-sealed, under-insulated attic warms the upper roof and melts the snow on it; that meltwater runs down to the cold eaves and overhang and re-freezes into a ridge of ice. Water then pools behind the dam and backs up under the shingles, where it can leak into the walls and ceilings below.
$1,500–4,000 to fix attic insulation/ventilation (less for minor air-sealing)Address soonRoofingInsulation
Why it matters
Ice dams cause recurring roof leaks, stained ceilings, soaked insulation, and rot — but the ice is the symptom. CMHC and Natural Resources Canada are clear that the root cause is heat and air leaking into the attic, so the real fix is air-sealing and insulating the attic floor first, with good attic ventilation as the second line of defence to keep the attic cold and dry. Treating only the ice (e.g. heat cables) means it's back next winter.
How to spot it
Thick ice ridges and large icicles at the eaves in winter; thin, patchy, or unevenly-distributed attic insulation; water stains on top-floor ceilings near exterior walls; and a roof where the snow melts unevenly (bare patches over warm, leaky spots).
What it costs
Usually $1,500–4,000 to air-seal, top up attic insulation, and improve ventilation; minor air-sealing alone is cheaper. Repairing water damage already done is extra.
What to do
Address soon in cold climates. Prioritise air-sealing + insulation (the cure) over heat cables (a band-aid), and ask the seller whether top-floor ceilings have ever leaked in winter.
Education and triage, not a home inspection. Casaroo flags ice-dam risk from attic-insulation and eave photos — an insulation or roofing professional confirms the fix.
Common questions
What is Ice damming?
A winter problem common in Canadian homes: heat leaking into a poorly air-sealed, under-insulated attic warms the upper roof and melts the snow on it; that meltwater runs down to the cold eaves and overhang and re-freezes into a ridge of ice. Water then pools behind the dam and backs up under the shingles, where it can leak into the walls and ceilings below.
Why does it matter for home buyers?
Ice dams cause recurring roof leaks, stained ceilings, soaked insulation, and rot — but the ice is the symptom. CMHC and Natural Resources Canada are clear that the root cause is heat and air leaking into the attic, so the real fix is air-sealing and insulating the attic floor first, with good attic ventilation as the second line of defence to keep the attic cold and dry. Treating only the ice (e.g. heat cables) means it's back next winter.
How can I spot it?
Thick ice ridges and large icicles at the eaves in winter; thin, patchy, or unevenly-distributed attic insulation; water stains on top-floor ceilings near exterior walls; and a roof where the snow melts unevenly (bare patches over warm, leaky spots).
How much does it cost to fix?
Usually $1,500–4,000 to air-seal, top up attic insulation, and improve ventilation; minor air-sealing alone is cheaper. Repairing water damage already done is extra.
A licensed insulation/roofing pro confirms; Casaroo flags, it does not inspect.
Last reviewed 2026-06-27.
Casaroo reviews each guide against current pricing, code, and insurer practice. Cost ranges are 2026
estimates that vary by region, size, and access — confirm specifics with a licensed professional.