What are the roof flashing requirements for valleys, walls and chimneys in Ontario?
The OBC requires flashing at every roof intersection: valleys, roof-to-wall junctions, chimneys and penetrations. Approved materials include sheet metal and roll roofing for valleys, with prescribed widths, laps and step-flashing methods to keep water out of joints.
Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.
Most roof leaks occur at transitions, not in the field of the shingles, which is why flashing gets its own subsection. Valleys need continuous metal or membrane-backed material of adequate width with generous laps. Where a roof meets a wall, individual step flashing pieces must be woven into each shingle course, then covered by cladding or counter flashing. Chimneys need base, step and counter flashing, with the counter flashing embedded or reglet-cut into the masonry. Caulking smeared over shingle-to-brick joints is not a code-compliant substitute and rarely lasts two winters.
Anywhere a roof meets a wall, chimney or another roof, the code requires overlapping metal pieces called flashing. These act like shingles for the joints, steering water back onto the roof instead of into the structure.
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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.