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Plywood and OSB wall sheathing are usually applied vertically and are often nailed to the wall framework before a wall is lifted into position. This helps maintain squareness, avoids the need for scaffolding, and speeds construction. Window openings may be covered by the sheathing panels that are cut when window installation occurs. When sheathing is applied horizontally, vertical joints should be staggered. There are two methods of installing sheathing down to the foundation sill so that it covers not only the walls, but the joist header space as well. One way is to extend the low end of the sheathing panel beyond the bottom wall plate and adding a filler piece at the top. Another way is to use longer 2.74 m (9 ft.) sheathing panels that cover the wall down to the sill area. It is better to cover the header and sill with the same wall sheet because this reduces air infiltration, and when structural panels are in place, it ties the framing to the sill plates. Leave a 2 to 3 mm (1⁄8 in.) wide space between the sheets to permit expansion. Nail the sheathing panels to the framing with nails
spaced not more than 150 mm (6 in.) on centre along the edges and 300 mm (12 in.) along the intermediate supports (Figure 107). Plywood is a structural panel made from wood veneers that are glued together so that the grain direction of each layer is perpendicular to the adjacent layers. The grain direction of the top and bottom surfaces is parallel to the length of the panel. Sheathing grade plywood is made with waterproof adhesive, unsanded, and may contain knots. The minimum thickness for exterior plywood wall sheathing is 7.5 mm (5⁄16 in.) for studs 600 mm (24 in.) on centre, and 6 mm (1⁄4 in.) for studs up to 400 mm (16 in.) on centre. Sheets are made 1.22 m (4 ft.) wide and usually 2.44 m (8 ft.) or 2.74 m (9 ft.) long. Fibreboard sheathing should be at least 11.1 mm (7⁄16 in.) thick for studs 600 mm (24 in.) on centre and 9.5 mm (3⁄8 in.) for studs 400 mm (16 in.) on centre. It is made in sheets 1.22 m (4 ft.) wide and generally 2.44 m (8 ft.) long, and is usually impregnated with an asphalt material to increase water resistance.
107 Vertical and horizontal application of panel-type sheathing Vertical application
Horizontal application
window opening
10 mm (3⁄8 in.) minimum edge distance to nail 2-3 mm (1⁄8 in.) space between sheets edge nail 150 mm (6 in.) o.c. nail 300 mm (12 in.) o.c.
nails 2-3 mm (1⁄8 in.) space between sheets edge nail 150 mm (6 in.) o.c. nail 300 mm (12 in.) o.c. foundation
Note: Closer nailing patterns required for high wind/earthquake exposures