What is the minimum roof slope for asphalt shingles and other roofing materials in Ontario?
The OBC sets minimum slopes by material: asphalt shingles need at least 1:3 in normal application, or 1:6 (about 2:12) using low-slope application methods. Flatter roofs require membrane systems such as built-up or modified bitumen roofing.
Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.
Slope drives everything in roofing design. Shingles shed water rather than seal it out, so on shallow pitches wind-driven rain and ponding will find the joints. Below 1:3 you must switch to low-slope shingle application, which typically means reduced exposure and cemented laps or full eave-to-ridge membrane underlayment. Below 1:6, shingles are off the table entirely and you need built-up, modified bitumen, EPDM or similar membranes. Porch and addition roofs are the most common spots where builders get caught with a pitch that is too shallow for the chosen product.
Shingles only work if the roof is steep enough for water to run off. In Ontario, a roof flatter than about 2-in-12 cannot have regular shingles at all; it needs a flat-roof membrane instead.
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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.