Egress Windows in Ontario: Minimum Size, Code & Cutting Requirements

What Is an Egress Window, and When Does Ontario Require One?

The egress window size requirements in Ontario call for an unobstructed opening of at least 0.35 m² (about 3.8 sq ft), with no single dimension under 380 mm (roughly 15 inches), openable from inside without tools. The Ontario Building Code requires a means of escape in every bedroom, so a legal basement bedroom usually means saw-cutting the foundation wall.

Because a basement wall is cast concrete or concrete block, creating that opening is a cutting job, not a framing job. Below is what the code asks for and how the foundation is saw-cut to make room for the window.

Egress Window Size Requirements in Ontario (OBC Minimums)

The Ontario Building Code (OBC 9.9.10.1) sets the opening a bedroom escape window has to provide. The widely referenced minimums are:

• Unobstructed opening area: at least 0.35 m² (roughly 3.8 sq ft).
• No single dimension less than 380 mm (about 15 inches) — a tall, skinny slot or a short, wide slot that only hits the number in one direction will not pass.
• Openable from the inside without keys, tools, or special knowledge, and without removing the sash.
• Window wells: if the window opens into a well, clearance is required in front of it (commonly cited around 550 mm) so a person can actually get out.

Treat those figures as the starting point. Code editions change and municipal building departments interpret the details their own way, so confirm the exact numbers for your project with your local building department before you order a window.

How the Foundation Wall Is Saw-Cut for an Egress Window

Most existing basement windows are too small for egress, so the real work is enlarging the rough opening in a concrete or block wall. Here is the sequence a professional crew follows.

1. Scan, then mark the opening

Before any blade touches the wall, we scan it. Ground-penetrating radar locates rebar, conduit, and buried services so the cut avoids surprises. We then mark the rough opening — the window unit plus its buck or frame — squarely on the wall.

2. Cut and lift out the concrete

A wall saw or track-mounted diamond saw makes clean, straight cuts through cast concrete foundations; block walls can be cut and broken out in sections. This is precision saw cutting rather than jackhammering, which keeps the surrounding wall intact and the edges square for the new frame. The freed concrete is then lifted out.

3. Support the opening with a lintel or header

A foundation wall carries load, so widening it removes structural material. Larger openings usually need a steel lintel or an engineered header above the window to carry the wall and floor above. For anything beyond a modest enlargement, an engineer’s detail may be required — your building department will tell you when.

Once the opening is cut and supported, the buck is set, the window unit is installed and sealed, and the exterior window well and drainage are added. Waterproofing at the fresh cut is critical to keep the basement dry.

Permits, Structure, and Planning

Adding or enlarging an egress window in a foundation almost always needs a building permit. The municipality reviews both the egress compliance and the structural detail above the opening. A few things worth planning for:

• Utilities and rebar: scanning first avoids cutting a live service line or a critical reinforcing bar.
• Water management: the window well needs drainage tied into the weeping system or a drainage pit.
• Grade and setbacks: the well has to sit correctly against exterior grade and lot lines.

Cutting a clean, correctly sized opening is the part we handle every week. If you are weighing how the concrete comes out, our explainer on cut-and-lift versus jackhammering and our overview of slab, wall, and wire sawing methods both cover the techniques used on egress jobs. You can see the wider scope on our residential concrete construction page.

Where Our Crews Cut Egress Windows

CDS has run from one Hamilton base since 1967, and our mobile crews travel across the region for residential egress work. We regularly cut and install egress windows for homeowners in Hamilton, throughout the Niagara Region, and in Brantford. See all of our cutting services for the equipment behind the work.

See all our concrete services.

Continue reading: Residential Concrete Contractor in Hamilton

Frequently Asked Questions

What is the minimum egress window size for a legal bedroom in Ontario?

The Ontario Building Code calls for an unobstructed opening of at least 0.35 m² (about 3.8 sq ft) with no dimension smaller than 380 mm (about 15 inches), openable from the inside without tools. If the window opens into a well, clearance is required in front of it. Always confirm the current figures with your local building department.

Do I need a permit to cut an egress window into my foundation?

In almost all cases, yes. Enlarging or adding a window in a load-bearing foundation wall is a structural change, so your municipality will want a permit and will review the lintel or header detail above the opening along with the egress sizing.

How is the concrete foundation actually cut for the window?

The wall is scanned to locate rebar and utilities, the opening is marked, and a wall saw or diamond saw makes straight, square cuts. The concrete is lifted out, a lintel or header is added if needed, and the window and exterior well are installed and waterproofed.

Can you cut an egress window in a cast concrete wall as well as block?

Yes. Both cast concrete and concrete block foundations can be cut for egress. Cast concrete walls are typically wall-sawn for clean edges; block walls can be saw-cut and removed in sections. Scanning the wall first matters on both.

Planning a basement bedroom or a walkout? Talk to the longest-running concrete cutting company in Ontario about your egress opening. Call CDS at (905) 529-6029 or request a quote, and we will size, cut, and install it to code.