Egress Window Requirements
for Basements and Bedrooms

The most expensive line item homeowners forget when budgeting a basement renovation is the egress window. They picture the finished bedroom; they do not picture the excavator parked on the front lawn cutting a 4-foot hole through 8 inches of poured concrete.

The Ontario Building Code is unambiguous: every habitable room and every bedroom needs an exit, and below grade that exit is almost always a window cut through the foundation. Skip it and the unit is not habitable. Get it wrong and the inspector fails the framing inspection.

Here is the rule, the math, and the real Ottawa numbers on what an egress window costs and how to make sure yours passes the first inspection.

The Rule: OBC 9.9.10.1

The governing section is Ontario Building Code 9.9.10.1, Egress from Bedrooms. It applies to every bedroom in a house, not just basement bedrooms. The requirements:

• Minimum unobstructed clear opening of 0.35 m² (about 3.77 sq ft)
• No dimension less than 380mm (about 15 inches) clear of any frame or obstruction
• Sill height not more than 1,000mm above the finished floor in bedrooms (1m)
• Operable from inside without tools, special knowledge, or removal of sash
• If the window opens into a window well, the well must be sized so the window can fully open

The same section applies to suites in residential buildings. Every habitable room without a direct exterior door needs a compliant exit window.

If you are designing a secondary dwelling unit, the egress requirement is per bedroom and per suite. A two-bedroom basement apartment with a separate exterior entrance has the entrance as the suite egress, plus each of the two bedrooms still needs its own bedroom egress window.

What "Clear Opening" Actually Means

This is where the inspector and the salesperson at the window store often disagree. The 0.35 m² is the clear unobstructed opening when the window is fully open. It is not the rough opening, not the frame size, and not the glass area.

For a casement window (hinged on the side), the clear opening is roughly the sash dimensions when fully cranked open. For a slider, it is half the rough opening width by the height. For a single-hung or double-hung window, only the openable section counts.

This is why casement windows dominate egress applications: they open more usable area for a given rough-opening size. A 32" x 36" casement gives you a clear opening of about 0.46 m². The same 32" x 36" rough opening as a slider gives you maybe 0.27 m² and fails the rule.

Window Well Dimensions

For basement windows below grade, the window well is part of the egress assembly. The OBC sets minimums:

• Window well floor area: minimum 0.55 m² (about 5.9 sq ft)
• Clearance in front of the window: minimum 760mm from the window face to the wall opposite, when the window is fully open
• If the well is more than 1.5m deep, a permanent ladder or steps must be installed
• Cover or grate is permitted as long as it is releasable from inside the well without tools

In practice this means the prefabricated 36" x 48" galvanized window well some homeowners buy off the shelf is too small to satisfy the rule. We typically install wells 48" x 60" or larger, often custom-formed concrete wells set into the existing foundation.

The Bedroom Sill Height Trap

The 1m sill height rule for bedrooms catches a lot of basement layouts. In a typical Ottawa basement with 7-8 ft ceilings, the bottom of the joist is around 7-8 ft above the floor. The header for a window has to land below the joist. The window has to be tall enough for the clear-opening rule. And the sill has to be at most 1m above the floor.

The math forces the window to be cut quite low into the foundation, often with the bottom of the window opening 50-200mm below the existing finished grade outside. That is why window wells are essentially mandatory for basement bedrooms in Ottawa: the window has to drop low enough that you are below grade.

What the Excavation and Cut Actually Involve

Cutting an egress window into an existing Ottawa foundation is a real job, not a trim-out. Here is the typical sequence:

1. Locate utilities and call Ontario One Call (free locate service) before any digging. Required.
2. Excavate the well location down to the planned sill elevation, often 4-6 feet below grade. Most jobs use a mini-excavator if there is rear-yard access; some require hand-digging in tight side yards.
3. Cut the foundation with a wet-cut diamond saw. Poured concrete is straightforward; concrete block and stone foundations are more variable. The cut is sized to the manufacturer's rough opening plus the new lintel allowance.
4. Install the steel lintel above the cut to support the load that was carried by the foundation wall. This is structural; it usually needs P.Eng review for older homes.
5. Frame the rough opening with treated lumber, set the window, flash, and seal.
6. Form and pour or install the window well, ensuring drainage to the perimeter weeping tile or to a dedicated drain.
7. Backfill, restore landscaping, install the well cover or grate.
8. Install interior finishes, insulate the window jambs, finish drywall and trim.

Each window is a 2-4 day job for a competent crew, and the work moves a lot of dirt and dust through the property.

What Drives the Cost in Ottawa

The cost of a single egress window cut into an existing poured-concrete foundation is driven by access and site conditions, not a flat rate:

• Simple installation, rear-yard access, soft soil, no obstructions: the lowest-cost scenario, because a mini-excavator can do the digging.
• Typical installation, side-yard or front-yard access, some obstructions, standard window well: mid-range, with more careful excavation around the property.
• Difficult installation, hand-dig only, near utilities, decorative landscaping to restore, custom window well: the highest cost, because the labour is slow and the restoration is extensive.

For projects with two or three windows the per-unit cost drops because mobilization and excavation are amortized across the openings. Each window adds a code-compliant bedroom that increases the rentable area significantly, which is how the math works in its favour on a basement legalization.

If you are doing a basement legalization where each bedroom needs its own egress, the egress windows often represent 15-25% of the total project budget. That is normal; it is the cost of converting "basement square footage" into "habitable bedroom square footage."

Common Ways Egress Windows Fail Inspection

From watching Ottawa City inspectors do their job for two decades, the recurring failure modes:

1. Window installed but the clear opening does not meet 0.35 m². Owner thought the rough opening was the relevant number. Fix: replace window. Expensive.
2. Window well too small. Prefab kit was 36" x 36"; the rule needs 0.55 m² floor area. Fix: cut larger well. Significant rework.
3. Sill height over 1m in a bedroom. Fix: cut the foundation deeper, lower the sill. Major rework.
4. Window well lacks drainage. Inspector sees standing water in the well at framing inspection. Fix: connect to weeping tile, add gravel base, ensure positive drainage.
5. No structural calc for the lintel above the cut. Fix: get P.Eng review and revised drawings, then resubmit.
6. Window well cover requires tools to release from inside. Fix: replace cover with code-compliant releasable model.

"The egress window is the cheapest insurance policy you will ever buy. It is the difference between a bedroom and a storage room, and it is the difference between an inspector signing off on your basement and ordering it gutted."

Egress for Above-Grade Bedrooms

The 9.9.10.1 rule is not basement-specific. Every bedroom in a house has to meet the same egress rule, with one practical exception: bedrooms that already have a direct exterior door (rare in Ottawa houses) or bedrooms in a building with a sprinkler system that meets specific OBC criteria.

For typical Ottawa homes, this means second-floor bedroom windows also have to meet 0.35 m² clear opening, 380mm minimum dimension, and 1m sill rule. Modern builder windows nearly always satisfy this; older homes (pre-1990) often have tilt-out hopper windows or smaller awning windows in second-floor bedrooms that do not meet the rule. If you are renovating a vintage Ottawa property and adding or upgrading bedrooms, plan to verify the egress in every bedroom, not just the new ones.

Window Well Drainage

One detail nobody talks about until the first heavy rainfall: the window well needs to drain. A poorly drained well fills with water during a Spring melt and either floods the basement bedroom or rusts out the window over a few seasons.

The two acceptable approaches:

• Tie the well into the perimeter weeping tile with a 4" perforated pipe and gravel base. This is the long-term reliable solution but requires accessing the weeping tile during the well install.
• Dedicated drain pit below the well floor, 2-3 ft deep, filled with clear stone, allowing percolation into the surrounding soil. Works in well-draining soils; less reliable in Ottawa's clay-heavy areas.

Either way, the well floor itself should be 4-6 inches of clear stone, not bare soil, with the window sill at least 150mm above the floor of the well.

What the City Inspector Will Check

At the framing inspection (after framing, before insulation), the City of Ottawa inspector will verify:

• Window manufacturer and model match the permit drawings
• Clear-opening dimensions match the manufacturer's published egress data
• Sill height in bedrooms is ≤ 1m
• Lintel size and type match the structural drawings (P.Eng-stamped if applicable)
• Window well dimensions meet 9.9.10.1
• Drainage from the well is visible (or the next inspection will check it after backfill)
• Cover or grate is releasable from inside without tools

Bring the window manufacturer's spec sheet to the inspection. Inspectors appreciate the speed-up and you get a clean approval.

The Bottom Line

Egress windows are not optional for any habitable basement room in Ontario. They are a real construction cost driven by access and site conditions, they require a structural review, and they are the single most common reason basement renovations fail their first inspection.

Get the design right with a BCIN designer, specify casement windows with published egress data sheets, install proper window wells with drainage, and budget honestly for the work. A code-compliant egress window is the literal foundation of every legal basement bedroom you will ever rent or sell.

For a basement legalization quote that includes the egress window costs honestly priced, call 613-862-4555 or use the contact form.