The Ontario Building Code | Thickness of Exterior Walls
18.104.22.168. Thickness of exterior Walls
(1) masonry exterior walls, other than cavity walls, in 1 storey buildings and the top storeysof 2 and 3 storey buildings shall be not less than 140 mm thick provided the walls are not more than 2.8 m high at the eaves and 4.6 m high at the peaks of gable ends.
(2) The exterior walls of the bottom storeys of 2 storey buildings, and exterior walls of the bottom 2 storeys of 3 storey buildingsshall be not less than 190 mm thick.
(3) In exterior walls composed of more than one wythe, each wythe shall be not less than 90 mm thick.