1. Except where the 1-in-50 hourly wind pressure is less than 0.8 kPa and the seismic spectral response acceleration, S_a(0.2), is less than or equal to 0.70, continuous lumber or panel-type roof sheathing shall be installed to support the roofing.

1. Wood-based panels used for roof sheathing shall conform to the requirements of
   1. CSA O121, "Douglas Fir Plywood,"
   2. CSA O151, "Canadian Softwood Plywood,"
   3. CSA O153, "Poplar Plywood,"
   4. CSA O325, "Construction Sheathing," or
   5. CSA O437.0, "OSB and Waferboard."

1. Plywood roof sheathing shall be installed with the surface grain at right angles to the roof framing.
2. OSB roof sheathing conforming to CSA O325, "Construction Sheathing," or to O-1 and O-2 grades as specified in CSA O437.0, "OSB and Waferboard," shall be installed with the direction of face orientation at right angles to the roof framing members. (See Note A-9.23.15.4.(2).)

1. Panel-type sheathing board shall be applied so that joints perpendicular to the roof ridge are staggered where
   1. the sheathing is applied with the surface grain parallel to the roof ridge, and
   2. the thickness of the sheathing is such that the edges are required to be supported.
2. A gap of not less than 2 mm shall be left between sheets of plywood, OSB or waferboard.

1. Lumber roof sheathing shall not be more than 286 mm wide and shall be applied so that all ends are supported with end joints staggered.
2. Lumber roof sheathing shall be installed diagonally, where
   1. the seismic spectral response acceleration, S_a(0.2), is greater than 0.70 but not greater than 1.2, or
   2. the 1-in-50 hourly wind pressure is equal to or greater than 0.80 kPa but less than 1.20 kPa.
3. Lumber roof sheathing shall be designed according to Part 4, where
   1. the seismic spectral response acceleration, S_a(0.2), is greater than 1.2, or
   2. the 1-in-50 hourly wind pressure is equal to or greater than 1.20 kPa.

1. Where panel-type roof sheathing requires edge support, the support shall consist of metal H clips or not less than 38 mm by 38 mm blocking securely nailed between framing members.

1. The thickness or rating of roof sheathing on a flat roof used as a walking deck shall conform to either Table 9.23.15.5.-A or Table 9.23.15.5.-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 9.23.16.7.-A or Table 9.23.16.7.-B.
3. Asphalt-coated or asphalt-impregnated fibreboard not less than 11.1 mm thick conforming to CAN/ULC-S706.1, "Wood Fibre Insulating Boards for Buildings," is permitted to be used as a roof sheathing over supports spaced not more than 400 mm o.c. provided the roofing consists of
   1. a continuous sheet of galvanized steel not less than 0.33 mm in thickness, or
   2. 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.

Table 9.23.16.7.-A
Thickness of Roof Sheathing
Forming Part of Sentence 9.23.16.7.(2)

Table 9.23.16.7.-B
Rating for Roof Sheathing When Applying CSA O325
Forming Part of Sentence 9.23.16.7.(2)