Enlarging a basement window: what the building code says

2026-01-28 — Ottawa-Gatineau

Want to turn your basement into a bedroom, office or rental unit? In most cases, the building code requires an egress window — and the original small horizontal window almost never qualifies. Here are the rules to know.

Why an egress window?

In a fire, every bedroom needs a usable emergency exit. In a basement, that's usually the window — so it must be big enough for an adult to get through.

Minimum dimensions (Ontario — OBC)

• Minimum unobstructed opening: 0.35 m² (3.8 sq ft)
• No dimension under 380 mm (15")
• Must open from the inside, without tools
• If the window opens into a window well: at least 760 mm (30") of clearance in front

And in Quebec?

Requirements are very similar: at least 0.35 m² of clear opening, no dimension under 380 mm. Cities like Gatineau apply the Quebec Construction Code — always check with your city before cutting.

Do you need a permit?

• Ottawa: yes, enlarging an opening in a foundation wall generally requires a building permit (structural modification)
• Gatineau: a permit is also required to modify an opening in an exterior wall
• Good news: the process is simple for this type of work, and the contractor can guide you

Typical project sequence

• Verify required dimensions for your project
• Permit (if required)
• Excavation and cutting — see our service →
• Window well and window installation
• Inspection and compliance

A code-compliant basement bedroom can add tens of thousands of dollars to your home's value — and let you rent legally.