Date of Publication: August 19, 2025 [2022.10.V-02.C]
Subject: Sheathing Requirements for Walls Outside the Scope of Table 9.23.10.1. 2024 OBC UPDATE
Summary of updates: Numbering of Tables referenced in Article 9.23.10.1. Recommendation remains unchanged.
2024 Ontario Building Code [O.Reg 163/24 Amended to 5/25] Reference(s):
Article 9.23.10.1. of Division B
Sentence 9.35.4.1.(1) of Division B
Sentence 9.23.10.1.(1) of Division B
Incoming Request:
Table 9.23.10.1.: Stud Sizing.
When sizing studs that fall outside of this Table (eg. Taller than the specified maximum unsupported height), we are referred to Tables 9.23.10.1.-A to 9.23.10.1.-D at the back of Part 9. Footnote 2 on these tables states that “Wall construction shall conform to the requirements of Sentence 9.23.10.1.(2).” Clause 9.23.10.1.(2)(a) states in part…”studs are clad with…not less than 12.5mm gypsum board on the interior face”. We tend to receive pushback from designers/property owners who feel that the interior of garages do not need to be finished based on Sentence 9.35.4.1.(1) which states: “Interior finish need not be applied to garage and carport walls, especially if the garage is a detached accessory building.”
Is gypsum board specifically required on the interior face of a wall whose studs fall outside of Table 9.23.10.1.?
Executive Summary:
Where an exterior wall that does not meet the configurations listed on Table 9.23.10.1. is designed to the stud sizes in Tables 9.23.10.1.-A to 9.23.10.1.-D:, sheathing of minimum 12.5 mm gypsum sheathing is required on the interior face of the wall in addition to the normally required exterior sheathing.
Discussion & Considerations:
Article 9.23.10.1. and Table 9.23.10.1. prescribe spacing, size and maximum unsupported height of wall studs. Sentence (2) of the Article allows a wall that does not fit the parameters of Table 9.23.10.1. to be designed using studs from Tables 9.23.10.1.-A to 9.23.10.1.-D:. Sentence (2) also states, among other details, that the wall must have exterior sheathing and 12.5 mm interior gypsum sheathing.
A review of Appendix A – 9.23.10.1. (2) Tall Stud Walls provides confirmation that without the interior sheathing, the tall wall will not comply with CSA O86 Engineering Guide for Wood Frame Construction. The design assumptions for the prescriptive code sentence take into consideration the horizontal and vertical design loads applied to the wall assembly (roof, floors and wind). To pass the criteria outlined in CSA O86, the assembly must pass minimum requirements for both the bending moment and compression resistance parallel to the grain.
Furthermore, the supposed “exemption” provided by Sentence 9.35.4.1.(1) clearly is intended to relieve a garage from the interior finish requirement, not the structural requirement.
Risk/Benefit Analysis:
Requiring interior drywall (or an equal sheathing membrane) on the interior of a garage wall is an added expense for an applicant, however it is clearly required for the structural sufficiency of a “tall wall” outside of Table 9.23.10.1. To permit the omission of the interior sheathing would put a municipality at risk.
Final Recommendation:
Sentence 9.23.10.1.(2)(a) is applicable to the walls of a garage, in spite of an apparent exemption found in Sentence 9.35.4.1.(1).
Recommendation to Ministry of Municipal Affairs and Housing:
None at this time.
Referenced Documents:
- 2024 OBC Article 9.23.10.1. of Division B
- 2024 OBC Sentence 9.35.4.1.(1) of Division B
- 2024 OBC Sentence 9.23.10.1.(1) of Division B
Disclaimer:
This guidance document is intended to assist building officials by gathering relevant information to interpret the OBC Act and the prescriptive requirements of the Ontario Building Code, and is intended to be a best practice aid for building officials.
The views expressed within this guidance document should not be considered as the official interpretation of legislated requirements based on the Ontario Building Code, as the final responsibility for interpretation rests with the local Authority Having Jurisdiction.
The views of this advisory committee should not be construed as legal advice.