Where is ice and water shield (eave protection) required on roofs in Ontario?
Eave protection must run from the roof edge at least 900 mm (35 in) up the slope, and reach a line at least 300 mm (12 in) inside the inner face of the exterior wall, to guard against ice damming.
Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.
Ice damming happens where attic heat melts snow and the meltwater refreezes at the cold eave, backing water up under shingles. The membrane creates a sealed zone so that trapped water cannot reach the sheathing. On homes with wide overhangs, remember the 300 mm past-the-wall rule can push the membrane well beyond a single 914 mm roll width, so two courses are often needed. Valleys typically get membrane as well under flashing requirements. Skipping eave protection over a heated space is a common inspection failure on reroofs and additions.
That sticky rubberized strip along the bottom edge of the roof is required by code. It has to run about a metre up the roof and past the wall below, so melting snow that backs up behind ice cannot leak into your house.
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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.