Secondary Suite Egress Window Requirements: Sizing, Well Depths, and What Fails Inspection

Every bedroom in a secondary suite needs an egress window that meets Ontario Building Code requirements: a minimum unobstructed opening of 0.35 square metres with no single dimension less than 380mm, a sill height no more than 1500mm above the finished floor, and if below grade, a window well at least 760mm deep from the building face with proper drainage. The window most basements already have almost never qualifies. On roughly eight out of ten basement suite applications we review, the existing windows need to be enlarged or replaced entirely—and the window well work that follows is often the most disruptive part of the project.

The Actual Numbers: OBC Egress Window Dimensions

The Ontario Building Code section 9.9.10.1 sets the egress requirements for bedrooms in secondary suites. These numbers are non-negotiable, and inspectors arrive with tape measures. The minimum unobstructed opening area is 0.35 square metres, which works out to about 3.77 square feet. But here's where projects fail: that opening also cannot have any dimension smaller than 380mm. You can't have a tall, narrow slot or a wide, shallow strip—both dimensions must clear 380mm while the total area hits 0.35 square metres.

What trips people up is the word unobstructed. This isn't the rough opening in your foundation wall. It's not the frame size. It's the actual clear space when the window is fully open. For a casement window, that's the entire opening when the sash swings out. For a slider, it's only the portion that actually opens. For a double-hung, it's the clear space when one sash is raised. That double-hung window that looks plenty big? When you measure the actual opening with one sash up, it often comes in well under the required area.

Why Standard Basement Windows Fail

Most basement windows installed before secondary suite conversions became common were designed for light and ventilation, not emergency egress. A typical hopper-style basement window might have a 600mm by 400mm frame, but the actual clear opening when tilted in is nowhere close to 0.35 square metres. Slider windows are slightly better but usually fail on the minimum dimension requirement—the half that opens is often narrower than 380mm even when the total frame looks adequate.

• Hopper windows: The tilt-in design dramatically reduces the clear opening area, often to less than half the frame size.
• Horizontal sliders: Only half the window opens, and that half frequently measures under 380mm in one dimension.
• Awning windows: Similar problem to hoppers—the swing-out sash blocks part of the opening.
• Double-hung windows: The clear opening is limited to one sash, and the divided area rarely hits 0.35 square metres.

Casement windows are the most reliable choice for egress compliance because the entire sash swings out of the way, giving you the full frame opening. A casement window with a 500mm by 700mm clear opening provides 0.35 square metres exactly—meeting both the area and minimum dimension requirements.

Window Well Requirements: Depth, Width, and Drainage

If your egress window is below grade—which it almost certainly is in a basement suite—you need a window well that meets its own set of code requirements. The well must project at least 760mm from the building face, measured from the window to the outer edge of the well. The clear width must be at least 550mm, giving a person enough room to climb out. And if the well is deeper than 600mm from grade to the bottom, you need a permanently attached ladder or steps.

The drainage requirement catches many projects. Window wells cannot be allowed to accumulate water. This means either a drain connected to the weeping tile system, a sump with a connection to interior drainage, or in some cases a gravel base deep enough to handle expected water infiltration. Inspectors will ask about drainage, and if your well is just a hole with no drainage plan, the inspection fails.

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The window well is often more work than the window itself. You're excavating against the foundation, waterproofing the exposed wall, installing drainage, and then fitting a well that meets all the dimensional requirements. Budget accordingly.

Window Well Materials and Installation

Corrugated metal wells are the most common choice, but they need to be sized correctly and installed with proper clearances. The well must be anchored to the foundation wall to prevent movement, and the top edge should sit slightly above grade to prevent surface water from draining in. Many prefabricated wells are designed for standard window sizes that don't match egress requirements—you may need a custom-sized well or a larger prefab unit than you initially expected.

The space between the window and the well wall matters too. You need enough room for a person to maneuver through the window and into the well. A well that technically meets the 760mm projection but has a window that opens outward into that space doesn't provide adequate clearance. The inspector is thinking about a firefighter in gear or a panicked occupant in the dark—the geometry needs to work for real emergency egress, not just on paper.

Sill Height: The Requirement That Catches Deep Basements

The bottom of the egress window's clear opening cannot be more than 1500mm above the finished floor. In a typical basement with 7-foot ceilings, this usually isn't a problem—your window is probably around 1200mm up. But in deeper basements, especially older homes with lower ceiling heights where the window sits high on the wall, you may find the sill height exceeds the limit.

This is measured from the finished floor to the bottom of the clear opening, not to the window frame or sill. If you're adding a raised subfloor for insulation or radiant heating, that floor height increase directly affects your sill height measurement. A window that was compliant with the concrete slab might exceed 1500mm once you add a 100mm insulated subfloor.

Solutions for High Sill Heights

When sill height is a problem, you have two options: lower the window or raise the floor less. Lowering the window means cutting into the foundation wall—significant structural work that requires engineering review and typically adds substantially to your project scope. Reducing your floor assembly thickness might compromise your insulation goals or eliminate the radiant heating you planned.

At PermitsHub, we see this conflict regularly when preparing secondary suite drawings. The best approach is identifying the sill height issue early, before you commit to a floor assembly design. Sometimes shifting the bedroom location to a different part of the basement where window placement is more favorable solves the problem without foundation work.

What Actually Fails Inspection: The Common Deficiencies

Having reviewed hundreds of secondary suite inspection reports across the GTA, we see the same egress failures repeatedly. Understanding these patterns helps you avoid them.

Measurement Method Errors

The most common failure is measuring the wrong thing. Homeowners measure the rough opening in the foundation, the window frame exterior dimensions, or the glass size—none of which matter. The inspector measures the actual clear opening when the window is in its fully open position. For casements, this means the sash swung completely out. For sliders, this means only the operable portion. That beautiful new window you installed might have a 900mm by 600mm frame but only a 400mm by 500mm clear opening when you account for the frame thickness and the portion that doesn't open.

Hardware and Operation Issues

Egress windows must be operable from the inside without tools, keys, or special knowledge. Window locks that require a key fail. Complicated multi-step opening mechanisms fail. Windows painted shut obviously fail. The inspector will ask the occupant—or you—to open the window during inspection. If it sticks, jams, or requires unusual effort, expect a deficiency notice.

• Security bars without quick-release mechanisms from inside: immediate failure.
• Casement cranks that are broken or require excessive force: failure until repaired.
• Windows that have settled and no longer open fully: failure until adjusted.
• Storm windows or screens that cannot be removed from inside: failure.

Window Well Deficiencies

Window well failures often relate to drainage or dimensions. A well that meets the minimum projection but has no visible drainage plan will be flagged. Wells that have accumulated debris, soil, or standing water demonstrate drainage failure. Wells that are too narrow for practical egress—even if they technically meet the 550mm minimum—may be questioned if the window configuration makes actual egress difficult.

The ladder or step requirement for wells deeper than 600mm is frequently missed. A deep well with smooth metal sides and no climbing assistance fails. The ladder must be permanently attached—a removable step stool doesn't count. Rungs or steps need to be spaced appropriately for climbing and extend from the bottom of the well to within reach of the top edge.

Getting It Right: The Process for Compliant Egress Windows

Start by measuring what you have. Open your existing basement windows fully and measure the actual clear opening. Compare against the 0.35 square metre minimum and the 380mm minimum dimension. If you're short on either, plan for window replacement. Then measure from your planned finished floor height to the bottom of where the clear opening would be—if it exceeds 1500mm, you have a sill height problem to solve.

For window wells, measure the current projection from the foundation wall and the clear width. If you're enlarging windows, you're almost certainly enlarging wells too. Factor in drainage—if you don't have weeping tile or a sump system the well can connect to, you need a drainage solution designed into the project.

Permit Drawing Requirements

Your permit drawings need to show egress window locations, sizes, and sill heights. Window well dimensions, drainage connections, and ladder details if required must appear on the drawings. The building department reviews these before issuing the permit—getting the details right on paper prevents inspection failures later. This is where working with a firm experienced in secondary suite permits pays off; the drawings need to demonstrate code compliance clearly enough that the plans examiner approves them without revision requests.

Municipal requirements can add layers. Toronto, Mississauga, and other GTA cities accept the OBC minimums but may have additional requirements for specific zoning overlays or heritage areas. Some areas with high water tables have stricter window well drainage requirements. Your permit drawings should reflect any local conditions that apply to your property.

Special Cases: Existing Windows, Heritage Properties, and Alternatives

Occasionally an existing window is close enough to compliant that modification rather than replacement works. If you have a slider where the operable portion is just under 380mm, sometimes the window can be replaced with a casement in the same rough opening, gaining the needed clear area without foundation work. This depends entirely on the existing rough opening size and the available casement window dimensions.

Heritage properties present unique challenges. If your home is designated or in a heritage conservation district, exterior changes including window enlargement may require heritage approval before the building permit. The heritage review focuses on maintaining historical appearance, which can conflict with the larger window sizes egress requires. Some heritage boards accept rear-facing egress modifications more readily than street-facing changes—discuss options early in your planning.

There is no code-compliant alternative to egress windows for bedrooms. You cannot substitute additional smoke detectors, sprinkler systems, or other fire safety measures for the egress requirement. If a room cannot have a compliant egress window, it cannot be a bedroom in your secondary suite. This sometimes forces layout changes—what you planned as a two-bedroom suite becomes a one-bedroom with a den because only one room can achieve egress compliance.

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We've seen projects where moving the bedroom to the other side of the basement saved thousands in foundation cutting and window well work. The egress window requirement should drive your layout, not the other way around.