1. Exterior walls and gable ends shall be sheathed when the exterior cladding requires intermediate fastening between supports or if the exterior cladding requires solid backing.

1. Where wall sheathing is required for the purpose of complying with this Section, it shall conform to either Table 9.23.17.2.-A or 9.23.17.2.-B. (See also Article 9.25.5.1.)

Table 9.23.17.2.-A
Wall Sheathing Thickness and Specifications
Forming Part of Sentence 9.23.17.2.(1)

Notes to Table 9.23.17.2.-A:
(1) See also Sentences 9.27.5.1.(2) to (4).
(2) The flame-spread rating of gypsum board shall be determined in accordance with CAN/ULC-S102, "Test for Surface Burning Characteristics of Building Materials and Assemblies."

Table 9.23.17.2.-B
Rating for Wall Sheathing when Applying CSA O325
Forming Part of Sentence 9.23.17.2.(1)

1. Gypsum sheathing, rigid insulation and fibreboard shall not be used for the attachment of cladding materials.

1. Lumber wall sheathing shall be applied so that all ends are supported.
2. Where lumber wall sheathing is required to provide bracing according to Article 9.23.10.2., it shall be applied with end joints staggered.

1. A gap of not less than 2 mm shall be left between sheets of plywood, OSB, waferboard or fibreboard.

1. Where the bottom portions of mansard style roofs are vented, the vertical framing members behind the sloping portions shall be considered on the same basis as exterior wall studs and shall conform to Articles 9.27.3.2. to 9.27.3.6.