Code Library › Volume 1 › Section 9.23 — Wood Frame Construction
PART 9 — HOUSING AND SMALL BUILDINGSUpdated for the 2024 Ontario Building Code

9.23.17.2.Thickness, Rating and Material Standards

(1) Where wall sheathing is required for the purpose of complying with this Section, it shall conform to Table 9.23.17.2.-A or Table 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) Minimum Thickness, mm(1) Type of Sheathing With Supports With Supports Material Standards 400 mm o.c. 600 mm o.c. Fibreboard (insulating) 9.5 11.1 CAN/ULC-S706.1 ASTM C1177 / C1177M Gypsum Sheathing 9.5 12.7 ASTM C1396 / C1396M(2) Lumber 17.0 17.0 See Table 9.3.2.1. Mineral Fibre, Rigid Board, Type 2 25 25 CAN/ULC-S702.1 OSB, O-2 Grade 6.0 7.5 CSA O437.0 OSB, O-1 Grade, and Waferboard, R-1 Grade 6.35 7.9 CSA O437.0 Phenolic, faced 25 25 CAN/CGSB-51.25-M CSA O121 Plywood (exterior type) 6.0 7.5 CSA O151 CSA O153 Polystyrene, Types 1 and 2 38 38 CAN/ULC-S701.1 Polystyrene, Types 3 and 4 25 25 CAN/ULC-S701.1 Polyurethane and Polyisocyanurate Type 1, faced 38 38 CAN/ULC-S704.1 Polyurethane and Polyisocyanurate Types 2 and 3, faced 25 25 CAN/ULC-S704.1 Notes to Table 9.23.17.2.-A: (1) See also Sentences 9.27.5.1.(2) and (3). (2) The flame-spread rating of gypsum board shall be determined in accordance with CAN/ULC-S102, “Standard Method of 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) Maximum Spacing of Supports, mm Panel Mark 400 W16 500 W20 600 W24

This provision includes a table — formatting is preserved from the source; refer to the official code for the authoritative layout.

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Code text is reproduced for reference from the Ontario Building Code (O. Reg. 163/24, 2024 Building Code Compendium). This page is provided for general information and is not an official copy. Always verify requirements against the official Ontario Building Code and confirm with your local building department.