The Ontario Building Code | Thickness or Rating
9.23.15.7. Thickness or Rating
(1) The thickness or rating of roof sheathing on a flat roof used as a walking deck shall conform to either Table 9.23.14.5.A. or Table 9.23.14.5.B. for subfloors.
(2) The thickness or rating of roof sheathing on a roof not used as a walking deck shall conform to either Table 9.23.15.7.A. or Table 9.23.15.7.B.
Table 9.23.15.7.A.
Thickness of Roof Sheathing
Forming Part of Sentence 9.23.15.7.(2)
| Item | Column 1 Maximum Spacing of supports, mm | Column 2 Minimum Thickness, mm Plywood and OSB, O-2 Grade Edges supported | Column 3 Minimum Thickness, mm Plywood and OSB, O-2 Grade Edges Unsupported | Column 4 Minimum Thickness, mm OSB, O-1 Grade and waferboard, R-1 Grade Edges supported | Column 5 Minimum Thickness, mm OSB, O-1 Grade and waferboard, R-1 Grade Edges Unsupported | Column 6 Minimum Thickness, mm Lumber |
| 1. | 305 | 7.5 | 7.5 | 9.5 | 9.5 | 17.0 |
| 2. | 406 | 7.5 | 9.5 | 9.5 | 11.1 | 17.0 |
| 3. | 610 | 9.5 | 12.5 | 11.1 | 12.7 | 19.0 |
Table 9.23.15.7.B.
Rating for Roof Sheathing When Applying CSA O325
Forming Part of Sentence 9.23.15.7.(2)
| Item | Column 1 Maximum Spacing of supports, mm | Column 2 | Column 3 |
| 1. | 406 | 2R16 | 1R16 |
| 2. | 508 | 2R20 | 1R20 |
| 3. | 610 | 2R24 | 1R24 |
(3) asphalt-coated or asphalt-impregnated fibreboard not less than 11.1 mm thick conforming to CAN/ulc-S706, "wood Fibre Thermal insulationhttp://thehandyforce.com/insulation/" title ="Toronto home insulation">insulation for Buildings", is permitted to be used as a roof sheathing over supports spaced not more than 406 mm o.c., provided the roofing consists of,
(a) a continuous sheet of galvanized steel not less than 0.33 mm in thickness, or
(b) a continuous sheet of aluminum not less than 0.61 mm in thickness.
(4) All edges of sheathing described in Sentence (3) shall be supported by blocking or framing.
9.23.16. wall Sheathing