Steel Lintels for Basement Egress Windows in Ontario

Enlarging a basement window for egress almost always means cutting a bigger opening in the foundation wall, and that opening usually needs a lintel designed for the wall and the loads above it. In concrete block walls this is often one or more steel angles or a steel section with the block cores filled at the bearings, and in poured concrete walls it is whatever the engineer details for the cut. The window itself must meet the 2024 Ontario Building Code egress rules: an unobstructed opening of at least 0.35 m² with no dimension under 380 mm.

The Ontario egress window rules

The egress requirement is in Article 9.9.10.1. of the 2024 Ontario Building Code. Unless a door on the same floor level as the bedroom gives direct access to the outside, every floor level containing a bedroom in a suite needs at least one outside window that:

• Opens from the inside without tools.
• Provides an unobstructed open portion of at least 0.35 m² (about 3.8 sq ft), with no dimension less than 380 mm (about 15 in).
• Stays open on its own, maintaining that opening without extra support.
• For sliding windows, meets the minimum dimension in the part that actually opens.

Two more rules matter for basements:

• Sill height. Above grade, the egress window's sill can be no more than 1,000 mm above the floor. Basement areas are exempt from that limit, but a high sill still makes escape harder, so many designers keep it low with a built-in step or platform.
• Window wells. Where the window opens into a well, there must be at least 550 mm (about 22 in) of clearance in front of the window. If the sash swings into the well, it can't reduce that clearance in a way that would restrict escape. A cover over the well must open from the inside without keys, tools or special knowledge.

The key word is "open portion". A window with a large frame can still fail if the sash, hinges or a fixed panel leave less than 0.35 m² of clear opening. Check the manufacturer's clear opening dimensions, not the rough opening.

Why most basement windows need a bigger opening

Older basement windows are typically short hopper or slider units set high in the wall, well below the egress minimums. Getting to 0.35 m² with 380 mm minimum dimensions usually means making the opening deeper (cutting down toward the floor), wider, or both. Cutting down is the common choice because it lowers the sill and gives more height, but it also takes more wall out below grade, which is why the window well and drainage become part of the job.

This often comes up when a basement bedroom is being added or a basement is being converted into a secondary suite. Secondary suites have other requirements (fire separations, exits, smoke alarms and more), so the egress window should be designed as part of the whole basement plan, not as a separate project.

What happens when you cut a foundation wall

A foundation wall does more than hold back soil. It carries the house: the rim joist and floor joists sit on it, brick veneer often bears on a ledge at the top, and beams or posts may land on or near it. When you widen or deepen an opening, the material that used to carry that load is gone, and the load has to be moved around the opening into the wall on either side.

Concrete block walls

Concrete block (CMU) walls are hollow unless the cores are filled, so they can't simply be cut and left to span. A new opening in a block wall typically needs:

• A lintel over the opening, commonly steel angles, a pair of angles bolted through the wall, a steel section, or a reinforced concrete or bond beam lintel, depending on the loads and the designer's preference.
• Solid bearing at each end, usually by filling the block cores below the lintel ends with grout or concrete so the lintel bears on solid masonry rather than hollow webs.
• Solid jambs, with the cores along the sides of the new opening filled to finish the cut edges and carry the concentrated load.

Foundation walls also resist soil pressure and often carry concentrated loads from beams and posts, so a lintel in a block foundation wall is normally sized by the designer or an engineer rather than read straight off the code tables. Our guide to steel lintel sizes under the Ontario Building Code explains what the tables do and don't cover.

Poured concrete walls

Cast-in-place foundation walls are solid, and the concrete above a modest opening can sometimes carry the load without added steel, but that depends on the wall thickness, the reinforcing (if any), the depth of concrete left above the opening, and what bears on top. Older poured walls may have little or no reinforcing. The engineer decides whether the opening needs a steel lintel fastened to the wall, a header in the framing above, or other strengthening.

The framing above

If the new opening reaches up to the top of the foundation, the rim joist and floor framing above may also need a header. A steel angle or beam is sometimes used there too. This is one more reason the design should look at the opening from the footing to the floor above.

How the job usually goes

The sequence is similar to a lintel installation in a brick wall, which we describe in detail in how a steel lintel is installed in an existing brick wall. For a basement egress window it typically runs:

1. Design. A designer or engineer checks the wall and the loads, sizes the window for egress, and details the lintel, bearing and any jamb reinforcement.
2. Permit. Enlarging an existing window or creating a new one generally needs a building permit. The City of Toronto, for example, lists both.
3. Utility locates and excavation outside for the window well.
4. Shoring of the floor framing and wall above, as the design requires.
5. Cutting the opening, usually with a saw so the edges stay clean and the wall isn't shattered.
6. Lintel and jambs. Filling cores, setting the lintel on its bearing, and fastening it as detailed.
7. Waterproofing and drainage around the new opening and in the well, tied into the foundation drainage.
8. Window, well and cover installed to the egress rules.
9. Inspections at the stages your permit requires.

This is structural work below grade, combining excavation, shoring and cutting a loaded wall. Hire people who do it regularly.

Ordering the lintel

Once the engineer has detailed the lintel, the steel is a small, quick order, and getting it right avoids holding up a crew with an open hole in the foundation. Send:

• The engineer's detail or the section size and length
• Any holes for through-bolts or anchors, and their spacing
• Whether angles are to be paired, welded to a plate or supplied loose
• The finish: steel below grade and around window wells sees moisture, so galvanizing is often specified
• How many openings, so all lintels arrive together and tagged

For more on finishes, weights and ordering details, see our guide to custom steel lintels in Ontario. If you are also replacing a basement beam or posts as part of the renovation, our article on the cost to install a steel beam in a basement covers that side of the job.

Getting your egress lintel made

We fabricate steel lintels, beams, posts and plates for basement renovations, cut and drilled to your engineer's detail, and deliver across the GTA and Ontario. Engineering services are available for projects that need them, so if you don't have a detail yet, tell us about the wall and the opening when you get in touch.

Request a quote for your egress window lintel, or see the steel products we supply.