Ontario homeowners face significant roof damage every winter from ice dams. This guide covers causes, prevention, and remediation costs for GTA properties.
What Causes Ice Dams in Ontario?
Ice dams form when warm attic air melts snow on the upper roof while eaves remain below freezing. Meltwater refreezes at the cold eave overhang, creating an ice barrier that forces water under shingles.
Primary causes include: insufficient attic insulation (below R-50 for Ontario), inadequate attic ventilation, thermal bridging at rafters, and air leaks at ceiling penetrations (pot lights, exhaust fans, attic hatches).
Prevention Strategies
- Upgrade attic insulation to R-60 in Ontario climate zones 5-6
- Ensure 1:150 ventilation ratio (intake soffit + ridge exhaust)
- Air seal all ceiling penetrations before adding insulation
- Install ice and water shield membrane on first 2m from eave per OBC
- Heat cables on gutters and downspouts for chronic problem areas
Remediation Costs (GTA 2026)
- Attic air sealing: $800-$2,500
- Attic insulation upgrade (blown-in): $1,200-$3,500
- Ice and water shield installation: $2-$4/sq ft
- Soffit and ridge vent installation: $1,500-$4,000
- Emergency ice dam removal (steam): $400-$1,200
Roof Drainage Requirements Under OBC
Ontario Building Code requires roof drainage to discharge at least 1.5m from foundation walls. Downspouts must connect to storm sewer or splash pads directing water away from structure.
For more detailed technical guidance see: Ontario Ice Dam Prevention and Roof Drainage Guide 2026: Causes, Solutions and Costs – Telegraph