Can joists be notched for Ottawa bathroom plumbing?

Joist notching for plumbing is permitted under the Ontario Building Code, but there are strict rules about where and how deep notches can be cut — getting this wrong can seriously compromise your floor's structural integrity.

The general OBC rules for joist notching follow these principles: notches should not be located in the middle third of the joist span (where bending stress is highest), depth is typically limited to no more than one-sixth of the joist's actual depth, and notches should not be closer to the support than the joist depth. However, City of Ottawa requirements may vary — confirm exact specifications with your licensed contractor or Ottawa Building Services before any cutting begins.

For bathroom plumbing specifically, drain lines are the most common reason contractors need to notch or bore through joists. A 3-inch or 4-inch drain line for a toilet, for example, often can't fit between joists without some modification. Boring holes through the joist web (rather than notching the edge) is generally preferred by structural engineers because it's less damaging to the joist's load capacity — holes are typically permitted up to one-third of the joist depth, centered vertically.

In older Ottawa homes — particularly those built before the 1970s with dimensional lumber — joists may already be undersized by modern standards, making any notching riskier. Engineered lumber joists (LVL, I-joists) common in newer builds have their own strict manufacturer rules and often cannot be notched at all without voiding their structural rating.

For a new basement bathroom rough-in, this is exactly the kind of work that requires a plumbing and building permit in Ottawa. A licensed contractor will plan drain routing to minimize structural impact, sometimes using a sewage ejector pump or re-routing to avoid problematic joist locations entirely.

If you're planning a basement bathroom or any renovation involving plumbing rough-in, Ottawa Bathrooms can assess your specific joist situation and handle the permit process. Request a free consultation to get the right plan before any cutting happens.