(1) Panel-type sheathing board shall be applied so that joints perpendicular to the roof ridge are staggered where,
(a) the sheathing is applied with the surface grain parallel to the roof ridge, and
(b) 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.