How much of a load-bearing stud can be drilled out in Ontario?

The 2024 Ontario Building Code (O. Reg. 163/24, clause 9.23.5.3.) says a load-bearing stud must keep at least two thirds of its depth after any notching or drilling. If the stud is reinforced, less may remain, but the reinforcement has to be designed to compensate.

That two-thirds rule applies to solid-lumber studs covered by Part 9. If the wall contains engineered members, we found no general limit for them in 9.23.5., so ask your designer before anything is cut into those.

A few things shape how this plays out on a real job. The location of the hole matters: a hole near the edge of a stud leaves less wood than one centred in it, even if the remaining depth clears two thirds. The trade doing the drilling, whether a plumber or an electrician, is responsible for staying within the rule, but if you are opening a wall or repairing framing afterward, a carpenter or designer should look at what was done before any new framing goes in. The clause also covers notches, not just round holes, so a square chase cut for a pipe is measured the same way.

If the stud has already been cut and you are not sure how much depth remains, a carpenter can measure and tell you whether a reinforcement plate or a sister stud is needed. Whether that repair needs a permit depends on how the City of Ottawa classifies the work: ottawa.ca lists structural repairs or alterations as permit work, so confirm with the City before the wall is closed up.

When you get a quote for this work, ask the carpenter to itemise each of these separately: design (if a designer is involved in sizing any reinforcement), the building permit, temporary support, materials, labour, patching and finishing, and disposal.