The Ontario Building Code | Undersized Lumber
9.3.2.8. Undersized Lumber
(1) Joist, rafter, lintel and beam members up to 5% less than the actual Canadian standard sizes are permitted to be used provided the allowable spans for the grade and species of lumber under consideration are reduced 5% from those shown in the span tables for full size members.
In Plain Language
Undersized lumber, meaning pieces that don't meet standard dimension requirements, may only be used under the specific conditions set out in this article.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.