In Markham, ice dams form when attic heat melts snow that refreezes at the cold eave. High-risk zones share three traits: 1½-story rooflines, under-insulated attics (R-30 or lower), and undersized eavestroughs. Fixes: seal attic bypasses, add R-60 insulation, install heat cable at problem eaves, and upsize downspouts to 3"×4". Same-week diagnostic + estimate available across Markham.
Markham sits in a freeze-thaw corridor — daytime highs above 0°C and overnight lows well below. That cycle is the exact condition ice dams need. A warm attic melts the snow layer against the roof deck; the meltwater runs to the unheated eave; it refreezes into a dam; the next melt pushes water uphill under the shingles. Damage shows up as ceiling stains, peeling paint at the top of exterior walls, and rot at the fascia.
Homes built before the 1990 Ontario Building Code update are the most at risk — those attics were insulated to roughly R-20 and rarely had continuous soffit-to-ridge venting. Newer builds fail when pot lights, bath fans, or attic hatches leak warm air into the attic.
Ice dam risk isn't uniform across Markham. Older housing stock, tree cover, and lot exposure to prevailing northwest winds all shift the risk profile. Below: risk read-outs for the neighborhoods we service most.
Most Ontario policies cover the interior water damage from an ice dam but not the ice dam itself, and repeated claims can trigger non-renewal. Fixing the root cause (insulation + venting) is usually cheaper than one deductible.
No. Heat cable is a symptom manager. Without attic air-sealing and proper insulation, dams will still form above the cable. Use it as a supplement, not a fix.
Same-day emergency steam removal across Markham. Do not chip ice with hammers or use rock salt on the roof — both void most shingle warranties.
Ontario's current target is R-60. Anything under R-40 is a strong ice-dam predictor.
Coverage by city
Free written quotes. Same-week booking across the GTA.
Quote in 3 quick taps.
Service · urgency · contact. A chimney expert replies in under 15 minutes.
