Ice dams form on GTA roofs every winter — and the damage they cause is often more serious than homeowners expect. Here's what causes them and how to stop them for good.
If you've noticed a thick ridge of ice at the edge of your roof after a cold snap — or icicles hanging from your eavestroughs that seem larger than they should be — you may be looking at an ice dam. They're common across the GTA, especially in older homes. And they cause real damage.
The good news: ice dams are almost always preventable. The bad news: the fix isn't a product you can buy at a hardware store. It requires addressing the root cause inside your attic.
An ice dam is a ridge of ice that forms at the edge of your roof (the eave) and prevents meltwater from draining off properly. Here's the sequence:
Poor insulation or air leaks allow warm air to warm the upper section of your roof from below.
Even when outdoor temperatures are well below freezing, the warm roof surface causes snow to melt.
The eave overhang has no heated space below it — it's as cold as the outside air. Water freezes here, building up into a dam.
The ice dam forces standing water backward, where it finds gaps under shingles and flashing, and enters the home — through the ceiling, walls, or both.
Ontario's climate is ideal for ice dam formation. Unlike Northern Ontario, which stays consistently cold, the GTA experiences frequent freeze-thaw cycles throughout winter — a day above zero followed by a week below. Every time the cycle repeats, conditions for ice dam formation reset.
Add to that the fact that much of the GTA's housing stock was built in the 1960s, 70s, and 80s — long before modern insulation standards — and you have thousands of homes with attics that are chronically under-insulated and under-ventilated.
Sometimes — but not always. Some home insurance policies cover "sudden and accidental" water damage from ice dams. Others classify it as a maintenance issue (because the root cause is inadequate insulation) and deny claims. Read your policy carefully, and don't assume you're covered. Prevention is significantly cheaper than remediation.
These reduce immediate risk but don't solve the problem. You'll be dealing with it every winter.
Address the cause and ice dams stop forming — permanently.
Every winter, homeowners cause significant shingle damage trying to chip ice off their roofs with axes, ice picks, or shovels. We understand the impulse — the ice dam is right there and you want it gone. But hard impacts on frozen shingles crack and fracture them. You can cause more damage removing the ice than the ice itself would have caused.
If you have a large ice dam with active or suspected water entry, call a professional. Safe, damage-free removal requires specific techniques and tools.
Properly insulating and ventilating your attic is one of the best investments a GTA homeowner can make. It eliminates ice dams. It reduces heating and cooling costs by 15–20%. It prevents attic mold. And it extends the life of your roof by keeping shingle temperatures more stable.
An attic insulation top-up to R-60 on a typical 1,200 sq ft bungalow can be done in a single day. It pays for itself in energy savings over a few years — and prevents thousands of dollars in potential damage.
Whether you need emergency winter service or want to address the root cause before next season, we're here. Available 24/7 for active leaks. Serving Thornhill, Aurora, Richmond Hill, Vaughan, Markham, and the GTA.
Call 24/7 for Emergency Service 416-889-0629