Roof Sheating Detail at a Valley and at a Chimney Opening

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.

Figure 99