How much does it cost to repair ductwork damaged by ice damming in a Toronto attic?

Repairing attic ductwork damaged by ice damming in a GTA home typically costs $500 to $3,000, depending on the extent of the damage, the type of ductwork, whether insulation needs replacement, and how accessible the affected area is. In severe cases where ice dam water has saturated duct insulation and caused mould growth, costs can reach $4,000 to $6,000 when professional mould remediation is involved.

Ice damming is a persistent problem in Toronto's freeze-thaw climate, and when ice dams form along roof edges, meltwater backs up under shingles and drips into the attic — directly onto ductwork running through that space. The most common damage includes saturated duct wrap insulation that loses its R-value and promotes mould growth, rusted galvanized steel duct connections, water-damaged duct board that becomes soft and crumbles, and flex duct outer jackets that tear or delaminate from repeated freeze-thaw cycles. A typical repair involves removing and replacing damaged duct insulation ($1.50 to $3.00 per square foot for R-8 duct wrap), resealing joints that have separated due to ice expansion ($150 to $400 per repair), and replacing any sections of ductwork that have rusted through or been crushed by ice weight ($300 to $1,500 per section).

Flex duct is particularly vulnerable to ice dam damage. When water saturates the fibreglass insulation layer inside flex duct, it compresses the insulation permanently, reducing its R-value even after drying. The inner plastic liner can also develop tears where ice has formed and expanded inside the duct. If your attic flex duct has been water-damaged, replacement is usually more cost-effective than repair — new flex duct runs $8 to $18 per linear foot installed, and a full replacement of damaged flex runs typically costs $1,000 to $2,500.

Before any repair work begins, the attic should be inspected for mould growth on ductwork, surrounding wood framing, and insulation. Water from ice dams creates ideal conditions for mould in the enclosed, poorly ventilated spaces around attic ductwork. If mould is found, professional remediation is required before ductwork repairs — this adds $1,500 to $3,500 depending on the affected area. Ontario regulations require professional mould remediation when affected areas exceed 10 square feet.

The critical long-term fix is addressing the ice damming itself, not just repairing the ductwork. Ice dams form when heat escaping from the living space warms the roof deck, melting snow that refreezes at the cold eaves. Ironically, poorly insulated ductwork in the attic contributes to ice damming — warm air leaking from duct joints heats the attic space, accelerating snowmelt on the roof. Sealing and insulating your attic ductwork with mastic at every joint and R-8 minimum duct wrap both protects the ducts and reduces the heat loss that causes ice dams in the first place.

Have a qualified contractor inspect all attic ductwork after any ice dam event, even if no water stains are visible from below. Toronto Ductwork can connect you with local professionals experienced in attic duct repair and insulation through the Toronto Construction Network.