Ontario Building Code 9.29: Plywood and Hardboard Interior Finish Standards for London, Ontario Construction
Sarah's Expert Insight
OBC Compliance Specialist
"Correctly identifying the support spacing for hardboard and plywood is a frequent point of inspection in the London and Oakville residential markets. At empcontracting.ca Inc. your construction contractor in London, Ontario, we ensure all edges are properly blocked—especially in Muskoka cottage builds where humidity fluctuations can cause inferior installations to buckle if OBC fastening schedules aren't strictly followed."
Section 9.29.6: Grooved Plywood Interior Finishes
The Ontario Building Code (OBC) sets strict parameters for plywood used as interior finishes to ensure both aesthetic quality and structural stability.
Grooving and Structural Integrity
According to 9.29.6.2., grooves in plywood must not penetrate through the face ply into the underlying layers unless the groove is directly supported by framing or furring. An exception exists when the grain of the face ply runs at right angles to supports; in these cases, deeper grooves are permitted if the plywood thickness is increased by the depth of the penetration.
Fastening and Nails (9.29.6.3.)
Standard plywood finishes must be fastened with at least 38 mm casing or finishing nails. Spacing requirements are 150 mm o.c. (on center) along edge supports and 300 mm o.c. along intermediate supports. If the plywood is serving as a braced wall panel, it must adhere to the more rigorous fastening requirements found in Sentence 9.23.3.5.(2).
Edge Support (9.29.6.4.)
All plywood edges must be supported by furring, blocking, or framing to prevent sagging or joint separation.
Section 9.29.7: Hardboard Finish Requirements
Hardboard finishes must meet the CAN/CGSB-11.3-M standard and follow specific thickness-to-span ratios.
Hardboard Thickness and Support (9.29.7.2.)
- 3 mm thickness: Permitted only when applied over a continuous backing.
- 6 mm thickness: Required for supports spaced up to 400 mm o.c.
- 9 mm thickness: Required for supports spaced up to 600 mm o.c.
Fastening and Edge Support (9.29.7.3. & 9.29.7.4.)
Hardboard is fastened using 38 mm casing or finishing nails with the same 150/300 mm spacing as plywood. Edge support via furring or blocking is mandatory unless the backing is continuous.
Section 9.29.8: Insulating Fibreboard Finish
Insulating fibreboard must conform to the CAN/ULC-S706.1 standard, ensuring the material meets fire and thermal resistance benchmarks for Ontario homes.
Disclaimer: This content is generated from the Ontario Building Code for educational purposes. Always consult with a licensed professional engineer or your local building department before starting any construction project in London, Ontario.