Tempo:
Valley Flashing A “valley flashing” should be installed where two roof slopes intersect to form a valley. Open valleys leave the middle of the flashing exposed (see Figure 123) and must be flashed with one layer of sheet metal at least 600 mm (24 in.) wide, or with two layers of roll roofing installed over continuous sheathing. The bottom layer is Type S smooth roll roofing or Type M mineral surface roofing (mineral surface down), at least 457 mm (18 in.) wide. Centre this layer on the valley and fasten along the edges with nails spaced 400 to 450 mm (16 to 18 in.) apart. Apply a 100 mm (4 in.) band of roofing cement along the edge of the bottom layer. Then apply a second strip of Type M mineral surface roll roofing approximately 914 mm (36 in.) wide over the first layer (mineral surface up). Fasten the top layer along the edges with enough nails to hold it in place until the shingles are applied. The roof shingles stop 100 to 150 mm (4 to 6 in.) from the centre of the valley, with the distance increasing from top to bottom.
flashing. Shingle nails must not be placed within 75 mm (3 in.) of the valley centre line at the ridge, or within 125 mm (5 in.) at the eaves. Rigid shingles should not be used in closed valley roofs or roofs that slope less than 1:1.2.
Stepped Flashing or Shingled, Stepped Base Flashing for Shingled Roofs Flashing must be provided at the junction between a roof and a masonry wall or chimney. The base flashing should extend at least 150 mm (6 in.) up the side of the chimney or masonry veneer. A common approach is to bend the top of the base flashing and imbed it at least 25 mm (1 in.) into the horizontal masonry joints. The flashing is installed on all sides of a chimney where it penetrates a roof. This flashing method does not direct any water that is inside the masonry to the exterior, and this water may leak into the chimney or wall.
Closed valleys are usually flashed with one layer of sheet metal. Each course of shingles is continued across the valley to conceal the
Stepped base flashing should be installed in pieces, following the roof slope. The flashing pieces (also called “flashing squares”) are overlapped like the roof shingles, and extend at least 100 mm (4 in.) under the shingles (Figure 124). One square is used at each shingle
123 Valley flashing
124 Stepped flashing
shingle-lapped, stepped counter flashing cut saw
two-ply membrane valley flashing
shingled stepped base flashing
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sheet-metal valley flashing
flashing. Shingle nails must not be placed within 75 mm (3 in.) of the valley centre line at the ridge, or within 125 mm (5 in.) at the eaves. Rigid shingles should not be used in closed valley roofs or roofs that slope less than 1:1.2.
Stepped Flashing or Shingled, Stepped Base Flashing for Shingled Roofs Flashing must be provided at the junction between a roof and a masonry wall or chimney. The base flashing should extend at least 150 mm (6 in.) up the side of the chimney or masonry veneer. A common approach is to bend the top of the base flashing and imbed it at least 25 mm (1 in.) into the horizontal masonry joints. The flashing is installed on all sides of a chimney where it penetrates a roof. This flashing method does not direct any water that is inside the masonry to the exterior, and this water may leak into the chimney or wall.
Closed valleys are usually flashed with one layer of sheet metal. Each course of shingles is continued across the valley to conceal the
Stepped base flashing should be installed in pieces, following the roof slope. The flashing pieces (also called “flashing squares”) are overlapped like the roof shingles, and extend at least 100 mm (4 in.) under the shingles (Figure 124). One square is used at each shingle
123 Valley flashing
124 Stepped flashing
shingle-lapped, stepped counter flashing cut saw
two-ply membrane valley flashing
shingled stepped base flashing
slo
pe
do w
n
sheet-metal valley flashing
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