The Ontario Building Code | Valley Flashing
188.8.131.52. Valley Flashing
(1) Where sloping surfaces of shingled roofs intersect to form a valley, the valley shall be flashed.
(2) Valley flashing shall be installed over continuous sheathing.
(3) Closed valleys shall not be used with rigid shingles on slopes of less than 1 in 1.2.
(4) Closed valley flashing shall consist of sheet metal, self sealing composite membranes consisting of polyethylene and bituminous material or one layer of either Type S smooth surface roll roofing or Type M mineral surface roll roofing (mineral surface down) not less than 600 mm wide, and nails shall not penetrate the flashing within 75 mm of its edge or 124 mm of the bottom of the valley centreline.
(5) Open valleys shall be flashed with,
(a) at least one layer of sheet metal not less than 600 mm wide, or
(b) no fewer than two layers of roll roofing.
(6) The bottom layer of roofing required in Sentence (4) shall consist of not less than Type S smooth roll roofing or Type M mineral surface roll roofing (mineral surface down) not less than 457 mm wide, centred in the valley and fastened with nails spaced not more than 450 mm o.c. located 25 mm away from the edges.
(7) The top layer of roofing required in Sentence (4) shall consist of not less than Type M mineral surface roll roofing (mineral surface up), 914 mm wide, centred in the valley, applied over a 100 mm wide strip of cement along each edge of the bottom layer, and fastened with a sufficient number of nails to hold it in place until the shingles are applied.