If you are finishing a basement and one of the rooms will be a bedroom, the window in it stops being a window and becomes an exit. That changes what is required of both the window and the well in front of it.
This is the part of the job people discover late, usually after the hole is dug.
The three numbers
Article 9.9.10.1 of the National Building Code sets out what a bedroom egress window has to provide:
- 0.35 m² of unobstructed opening — about 3.8 square feet, measured on the opening the window actually makes, not the size of the frame.
- 380 mm minimum in either direction — about 15″. A long narrow slot that hits the area figure still fails if one dimension is under this.
- 760 mm of clearance in front of the window — about 30″, measured out from the wall.
The first two are the window's problem. The third is the well's.
Why the 30-inch projection costs more
A 760 mm clear space is what the code asks for in front of an egress window, and a 30″ well gives 762 mm. A 24″ well gives 610 mm and fails, even on a window that would otherwise pass on its own.
That extra six inches of projection is more steel across the full width and height of the well, more forming time, and a heavier piece to ship. It is not a premium feature with a premium price — it is simply a bigger part. But it is the difference between passing inspection and digging the hole twice, which is why we keep the egress-ready sizes in their own collection rather than burying them in the general list.
The ladder question
A deep well can satisfy the clearance figure and still be difficult to climb out of. Where the drop is significant, a permanent ladder or steps inside the well is normal practice and some authorities will ask for it. This varies more by municipality than almost anything else in this article, so ask before you build rather than after.
Where the provinces differ
The National Building Code is a model. Provinces adopt it and then amend it, and municipalities administer the result. In practice:
- Ontario writes its own — the Ontario Building Code, not the national one. The figures are close but the OBC is what your inspector holds you to.
- Quebec works under the Code de construction du Québec, administered by the Régie du bâtiment du Québec.
- Alberta and British Columbia publish their own editions of the national code with provincial amendments.
- The rest largely adopt the national code with local amendments layered on top.
Every city page on this site names the governing document for that location, which at least tells you which book to open — see Toronto, Montreal, Calgary or Vancouver, or find yours in the directory at the bottom of the home page.
Renovations versus new construction
A common assumption is that egress rules only apply to new builds. They generally do not. Creating a bedroom where there was not one before is usually what triggers the requirement, whatever the age of the house. Enlarging the opening to meet it means cutting the foundation, which is structural work and normally needs a permit.
What to do, in order
- Confirm with your municipal building department what applies to your property. They have the final word, and the call is free.
- Check the window first — the opening area and the minimum dimension are the window's job, and no well can fix a window that does not open far enough.
- Then size the well: 30″ projection or greater, wide enough to clear the frame on both sides, deep enough that the lip finishes at grade. How to take the three measurements.
- Ask about a ladder if the well is deep.
When you are ready, the 30″ and 36″ projection wells are the ones that clear the requirement.
Figures quoted here follow NBC 9.9.10.1 and are general guidance, not a code ruling on your property. Provincial and municipal amendments vary and your building department decides what applies.