Tempo:
the same distance apart on centre as the shingle exposure. This method (Figure 98), commonly used in damp climates, permits air movement and allows shingles to dry between wettings, reducing the possibility of decay.
Roof Sheathing Details Where openings occur in the roof structure for interior chimneys, the roof sheathing and framing members should have a clearance of 50 mm (2 in.) on all sides from the finished masonry, or metal chimney for fire safety (Figure 99). This clearance may be reduced to 12 mm (1⁄2 in.) for exterior masonry chimneys. Roof sheathing should be securely nailed to the rafters and headers around the opening. Fit sheathing at valleys and hips to give a tight joint and securely nail it to the valley or hip rafter (Figure 99). This will provide a solid, smooth base for flashing (see Chapter 14).
EAVE PROTECTION Eave protection is achieved by installing a membrane along the edge of the roof to prevent water from entering the roof. It is not required over unheated garages and porches, on roofs with a slope of 1:1.5 or greater or in regions with 3,500 or fewer heating degree-days. Eave protection should extend at least 900 mm (36 in.) up the roof to a point at least 300 mm (12 in.) inside the inner face of the exterior wall. Eave protection is installed under the shingle starter course and is most often a self-adhering bituminous or roll roofing membrane. During cold weather, heat loss through the ceiling insulation combined with sun exposure may provide enough heat to melt the snow on a roof but not on the projecting eaves. Water from the melting snow can freeze and form ice dams at the eavestrough and roof
99 Roof sheathing detail at a valley and at a chimney opening
50 mm (2 in.) clearance around chimney header
rafter roof sheathing valley
ridge board ceiling joist plate stud
Roof Sheathing Details Where openings occur in the roof structure for interior chimneys, the roof sheathing and framing members should have a clearance of 50 mm (2 in.) on all sides from the finished masonry, or metal chimney for fire safety (Figure 99). This clearance may be reduced to 12 mm (1⁄2 in.) for exterior masonry chimneys. Roof sheathing should be securely nailed to the rafters and headers around the opening. Fit sheathing at valleys and hips to give a tight joint and securely nail it to the valley or hip rafter (Figure 99). This will provide a solid, smooth base for flashing (see Chapter 14).
EAVE PROTECTION Eave protection is achieved by installing a membrane along the edge of the roof to prevent water from entering the roof. It is not required over unheated garages and porches, on roofs with a slope of 1:1.5 or greater or in regions with 3,500 or fewer heating degree-days. Eave protection should extend at least 900 mm (36 in.) up the roof to a point at least 300 mm (12 in.) inside the inner face of the exterior wall. Eave protection is installed under the shingle starter course and is most often a self-adhering bituminous or roll roofing membrane. During cold weather, heat loss through the ceiling insulation combined with sun exposure may provide enough heat to melt the snow on a roof but not on the projecting eaves. Water from the melting snow can freeze and form ice dams at the eavestrough and roof
99 Roof sheathing detail at a valley and at a chimney opening
50 mm (2 in.) clearance around chimney header
rafter roof sheathing valley
ridge board ceiling joist plate stud
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