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Table 35 Minimum thickness of roof sheathing for sloping roofs1 Sheathing Thickness, mm (in.), for Truss or Rafter Spacing at 300 (12)
400 (16)
500 (20)
600 (24)
Plywood and OSB, O-2 grade
Supported2 edges
7.5 (5⁄16)
7.5 (5⁄16)
9.5 (3⁄8)
Unsupported edges
7.5 (5⁄16)
9.5 (3⁄8)
12.7 (1⁄2)
OSB, O-1 grade and waferboard R-1 grade
Supported edges
9.5 (3⁄8)
9.5 (3⁄8)
11.1 (7⁄16)
Unsupported edges
9.5 (3⁄8)
11.1 (7⁄16)
12.7 (1⁄2)
Panel mark (performance-rated panels)
Supported2 edges
-
1R16
1R20
1R24
Panel mark (performance-rated panels)
Unsupported edges
-
2R16
2R20
2R24
17 (11⁄16)
17 (11⁄16)
Lumber3
19 (3⁄4)
Notes for Table 35 1. The thickness of sheathing for flat roofs used as walking decks is the same as for subfloors (see Table 18). 2. Supported edges between panels by means of H clips or minimum 38 mm x 38 mm (2 in. x 2 in.) blocking between trusses or rafters. 3. For eastern white pine and red pine, minimum lumber grade is No. 4 common. For all other species, the minimum grades shall be standard or No. 3 common.