Notice: This site currently shows the 2012/2017 edition of the Ontario Building Code. The current legally effective code is the 2024 edition (O.Reg. 163/24), in effect since January 1, 2025. Confirm current requirements at ontario.ca.
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The Ontario Building Code | Trimmer Joists

9.23.9.6. Trimmer joists

(1) Trimmer joists around floor openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings shall be doubled when the length of the header joist exceeds 800 mm.

(2) When the header joist exceeds 2 m in length, the size of the trimmer joists shall be determined by calculations.

In Plain Language

Trimmer joists, which support the ends of header joists around an opening, must meet the requirements 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.