My HVAC installer cut a joist in my Kanata house, is that OK?

A cut joist is a structural concern that needs a carpenter or designer to look at in person before anything else happens. The Ontario Building Code (2024, O. Reg. 163/24) sets out what is and is not permitted when framing members are notched or drilled, and a joist that has been cut outside those limits needs to be assessed and likely repaired.

For solid wood floor joists, clause 9.23.5.1. says a hole must not be more than one quarter of the joist's depth and must be at least 50 mm from either edge. Clause 9.23.5.2. permits a notch on the top of a joist only within half the joist's depth of the bearing point, and the notch must not be deeper than one third of the joist's depth. A cut that goes beyond either of those limits, or a cut through the middle of the span, falls outside what the Code allows without increasing the member's depth or providing an engineered repair.

If the joist is an engineered I-joist or LVL, we found no general rule in clause 9.23.5. that applies to them. Ask the designer before anything else is done.

What to do now: have a carpenter look at the cut and describe exactly where it is along the span, how deep it goes, and what type of joist it is. If the cut is outside the Code limits, the joist needs a repair; ask who designs it. Whether a designer needs to be involved in sizing that repair is something the carpenter and, if needed, the City of Ottawa Building Code Services can tell you. "Structural repairs or alterations" appear on the City of Ottawa's permit list at ottawa.ca, so ask Building Code Services whether this repair requires a permit before work starts.

When you have two written quotes in front of you, set them side by side and check that each one spells out the scope of the repair in writing, names who is responsible for any design and who will apply for any permit if one is required, lists the materials being used, and covers patching the floor or ceiling finish and removing debris when the work is done.