The Ontario Building Code | Direction of Installation
220.127.116.11. 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.