Roof Sheathing Direction of Installation

(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.

Article Ontario Regulation 332/12 Building Code,   Information published by for educational purposes only.

Sheathing-grade plywood or OSB or lumber planks are applied over roof trusses, joists or rafters to provide a nailing base for the roof covering and lateral bracing of the roof framing.

Application of structural wood-panel roof sheathing

Source : Canada Mortgage and Housing Corporation (CMHC)