PART 9 — HOUSING AND SMALL BUILDINGSUpdated for the 2024 Ontario Building Code
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9.23.15.5.Subfloor Thickness or Rating
(1) Except as provided in Sentences (2) and (3), subfloors shall conform to Table 9.23.15.5.-A or 9.23.15.5.-B.
Table 9.23.15.5.-A
Thickness of Subflooring
Forming Part of Sentences 9.23.15.5.(1) and 9.23.16.7.(1)
Minimum Thickness, mm
Maximum Spacing of
Supports, mm Plywood and OSB, O-1 Grade, and
Particleboard Lumber
OSB, O-2 Grade Waferboard, R-1 Grade
400 15.5 15.9 15.9 17.0
500 15.5 15.9 19.0 19.0
600 18.5 19.0 25.4 19.0
Table 9.23.15.5.-B
Rating for Subfloor when Applying CSA O325
Forming Part of Sentences 9.23.15.5.(1) and 9.23.16.7.(1)
Panel Mark
Maximum Spacing of Supports, mm
Subfloor Subfloor Used with Panel-Type Underlay
400 1F16 2F16
500 1F20 2F20
600 1F24 2F24
(2) Where the finished flooring consists of not less than 19 mm matched wood strip flooring laid at right angles to joists
spaced not more than 600 mm o.c., subflooring shall be permitted to consist of not less than
(a) 12.5 mm thick plywood,
(b) 12.5 mm thick OSB conforming to O-2 grade,
(c) 12.7 mm thick OSB conforming to O-1 grade,
(d) 12.7 mm thick waferboard conforming to R-1 grade, or
(e) OSB conforming to 2R32 / 2F16 grade.
(3) Except where the flooring consists of ceramic tiles applied with adhesive, where a separate panel-type underlay or
concrete topping is applied to a subfloor on joists spaced not more than 400 mm o.c., the subfloor is permitted to consist
of not less than
(a) 12.5 mm thick plywood,
(b) 12.5 mm thick OSB conforming to O-2 grade,
(c) 12.7 mm thick OSB conforming to O-1 grade,
(d) 12.7 mm thick waferboard conforming to R-1 grade, or
(e) OSB conforming to 2R32 / 2F16 grade.
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.