OBC Egress Window Checker

TL;DR: In Ontario, a bedroom egress window must provide an unobstructed open portion of at least 0.35 m² (3.77 sq ft) with no dimension less than 380 mm (15″), openable from inside without tools (OBC 2024, 9.9.10.1.(1)). Above grade, the sill can be no more than 1 000 mm (39⅜″) above the floor (9.9.10.1.(2)). A basement bedroom window is exempt from the sill limit, and where it opens into a window well the well must provide at least 550 mm (21⅝″) of clearance in front of the window (9.9.10.1.(3)).

Bedroom Egress Windows — What the Code Actually Wants

A bedroom egress window is the one opening that has to save someone's life at 3 a.m. in a smoke-filled room. The OBC numbers look arbitrary until you picture the scenarios they were written for — a sleeping occupant on the floor below the smoke layer, a firefighter in full bunker gear trying to push a ladder through the opening from outside. Here is what every number in 9.9.10.1 is protecting, and where renovations quietly go sideways.

Every figure on this page comes from the Ontario Building Code 2024 (O. Reg. 163/24, as amended January 16, 2025), Division B, Article 9.9.10.1 — verified against the code text on April 15, 2026 by a Red Seal Carpenter (Ontario CofQ).

Why do bedroom egress windows need 0.35 m² in Ontario?

Every other room in a dwelling has an escape path through a door. A bedroom with the door closed is a sealed box, and when the hallway on the other side is full of smoke, the window becomes the only way out — and the only way a firefighter gets in. The 0.35 m² (about 3.77 sq ft) minimum in 9.9.10.1.(1)(b) is sized around a fully-kitted firefighter with a self-contained breathing apparatus (SCBA) on their back. The tank adds roughly 150 mm to a person's front-to-back depth, and the harness makes shoulders effectively wider. The area is chosen so an occupant of any reasonable size can exit and a rescuer carrying gear can enter through the same opening. It is not a minimum for the smallest person in the house — it is a minimum for the largest person who might need to come in and find them.

What is the minimum dimension for an egress window opening?

Area is a trap if you stop there. A 100 mm × 3 500 mm slot gives you 0.35 m² on paper and nobody, SCBA or not, fits through it. That is why 9.9.10.1.(1)(b) adds a second constraint: no dimension of the opening may be less than 380 mm (about 15″). Both rules run together — you need the area and every direction through the opening has to clear 380 mm. For a rectangle, that means roughly 380 mm × 922 mm (15″ × 36¼″) to hit exactly 0.35 m², though in practice you want margin so tolerances on trim and sash don't eat your clearance. A 600 mm × 900 mm opening gives you 0.54 m² and comfortable 380 mm-plus in every direction — that is where most code-compliant bedroom casements land.

Which window styles count for bedroom egress?

The rough opening is not the egress opening. The code speaks to the unobstructed open portion, and different sash styles give you radically different fractions of the frame. A casement is hinged on the side and swings a full 90° — the whole rough opening clears, so 100% of the advertised dimensions count. An awning is hinged at the top and typically stays open at ~45° on a friction arm, cutting vertical clearance in half — and the sash itself hangs in the exit path. Many inspectors will not accept an awning as bedroom egress; verify before you order one. A horizontal slider and a vertical single-hung both follow 9.9.10.1.(6): the 380 mm minimum applies to the openable portion, so the operable half of the window has to make the cut. A 600 mm-wide slider has a 300 mm operable sash — that fails 380 mm before you even talk about area. A slider satisfying 9.9.10.1 usually starts at 1 200 mm of frame width. Specify for the opening the window has to clear, not the opening in the wall.

How high can an egress window sill be above the floor?

A bedroom fire fills the upper half of the room with smoke first, and occupants survive by dropping low. The 1 000 mm (39″) maximum sill height in 9.9.10.1.(2) keeps the window reachable from the crawling position you are trying to stay in. If an existing window has a higher sill — common in older homes or in bedrooms added into what used to be a loft — you have three options. Build a permanent platform below the window so the effective floor-to-sill dimension meets 1 000 mm (built-in, not a movable step stool). Reframe below the sill and drop the rough opening. Or replace the unit with one whose sill drops to 1 000 mm or less. Note that 9.9.10.1.(2) exempts basement areas — a basement bedroom does not have the 1 000 mm limit, because the window there is usually high on the wall by geometry and expected to open into a well.

What are the window well requirements for a basement bedroom in Ontario?

A basement bedroom trades the sill-height rule for a window well clearance rule. According to OBC 2024 Sentence 9.9.10.1.(3), where the window opens into a window well, the well must provide at least 550 mm of clearance between the window and the opposite well wall — floor space for a person to stand up in after exiting. (A walkout basement window that sits fully above grade needs no well at all — the clearance rule only triggers when a well exists.) 9.9.10.1.(4) catches the common mistake: if the sash swings toward the well (an outswing casement is the usual culprit), opening the sash cannot reduce the 550 mm clearance below the minimum. A 600 mm-wide well works on paper until you hang a 500 mm-wide outswing casement in it. Wells deeper than about 1 500 mm need a fixed ladder or stepped configuration so an occupant can climb out unassisted — standard AHJ practice even where Part 9 doesn't hard-number it. Drainage is not optional: a plugged well fills with water, freezes, and turns the only escape into a locked ice skylight. Specify drain rock to footing drains and clear leaves every fall. Remember 9.9.10.1.(5) — any enclosure over the well has to be openable from the inside without tools, keys, or special knowledge. "I showed the tenant where the latch is" is not operable-without-special-knowledge.

How do I use this checker? A worked example

Measure the clear opening — the free air through the fully open sash, not the rough opening or the glass. Pick the room type and window style above, punch in width, height, and sill height (inches or millimetres), and the tool runs every sentence of 9.9.10.1 with a per-rule PASS/FAIL. Worked example: a 30″ × 48″ (762 × 1 219 mm) clear opening as a casement gives 0.93 m² — clears 0.35 m² three times over, both dimensions beat 380 mm, easy pass. The same frame as a horizontal slider has a 381 mm operable sash width — it passes the 380 mm minimum by 1 mm. One thicker replacement jamb and that bedroom fails. That is why the style pill matters as much as the tape measure.

What are the most common egress window failures?

The biggest renovation failure is confusing the rough opening with the clear opening. A 900 mm rough opening receives a vinyl replacement whose frame is 50 mm thick on each side and whose sash is another 25 mm inside that — clear opening drops to about 750 mm, and the operable-sash opening on a slider drops to about 375 mm. That 375 mm fails the 380 mm rule by 5 mm, and the whole bedroom fails its egress because of a retrofit that looked like a like-for-like swap. Always size the replacement to the clear opening, and for sliders and hungs to the operable-sash clear opening. Security bars without a quick-release are the other classic — a bar installed to keep burglars out turns the window into a sealed wall when the key is in a drawer across a smoke-filled hallway. 9.9.10.1.(5) covers protective enclosures over window wells; the same principle applies to any interior bar or grate, and inspectors write it up either way. Finally, watch for furniture and drapery blocking the window — a dresser wedged against the sill, a heavy blackout curtain, a bunk bed that blocks the sash swing all defeat the intent even if the measurements pass. Walk the bedroom at 3 a.m. with the light off and see if the window still opens. If it doesn't, the house isn't code-compliant regardless of what the tape measure says.

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About OBC Egress Window Checker

Per OBC 2024 Sentence 9.9.10.1.(1), every floor level containing a bedroom needs at least one outside window with an unobstructed open portion of at least 0.35 m² (3.77 sq ft), no dimension less than 380 mm (15″), openable from inside without tools — unless a door on that level gives direct access to the exterior. Above grade the sill must be within 1,000 mm of the floor (9.9.10.1.(2)); a basement window opening into a well needs 550 mm of clearance in front (9.9.10.1.(3)).

By the ToolFluency team · Updated September 2026

Free Ontario Building Code 2024 bedroom egress window checker. Verifies clear opening area, minimum dimension, sill height, and basement window-well clearance against OBC 9.9.10.1. Casement, awning, slider, and hung windows — imperial or metric input.

How to use

Pick the room tab — above-grade bedroom or basement bedroom. Basement removes the sill-height limit but adds the window-well rule.
Choose the window style: casement, awning, horizontal slider, single-hung, or double-hung. Sliders and hungs only count their operable half toward 380 mm minimum.
Enter the clear opening width and height in inches or millimetres — the unobstructed openable portion, not the rough opening or the frame size.
Enter the sill height above the finished floor — capped at 1,000 mm for above-grade bedrooms per 9.9.10.1.(2); basement areas are exempt.
For basement bedrooms, enter the well width (clearance from window face to opposite wall — minimum 550 mm) and well depth — the tool flags wells over ~1,500 mm that need a fixed climb-out ladder.

Examples

Above-grade casement, 760 × 900 mm

760 × 900 mm clear opening = 0.68 m² → passes 0.35 m². Both dimensions exceed 380 mm. Sill at 900 mm above floor (under 1,000 mm cap). Casement = 100% of opening usable. PASS.

Basement slider, 1,200 mm wide × 600 mm tall

Slider operable half = 600 × 600 mm → 0.36 m². Both dimensions exceed 380 mm → operable area passes. Need 550 mm clear window well — a 600 mm well with an outswing casement would FAIL 9.9.10.1.(4). Slider passes.

Frequently asked questions

What is the minimum egress window size in Ontario?

Per OBC 9.9.10.1.(1), every floor level containing a bedroom needs at least one outside window (or a door on that level giving direct access to the exterior) with an unobstructed open portion of at least 0.35 m² (~3.77 sq ft) and no dimension less than 380 mm (~15″). The window must be openable from the inside without tools, and both rules — area AND minimum dimension — must be met.

What is the maximum sill height for a bedroom egress window?

OBC 9.9.10.1.(2) caps the sill height of an above-grade bedroom egress window at 1,000 mm (39.4″) above the finished floor. Basements are exempt from the sill rule — and where a basement window opens into a window well, 9.9.10.1.(3) requires at least 550 mm of clearance in front of it. Older homes with high sills can comply via a permanent built-in platform that brings the effective sill below 1,000 mm.

Do horizontal sliders and hung windows count for egress?

Yes — but only the openable portion counts. Per 9.9.10.1.(6), the 380 mm minimum dimension applies to the operable sash, which on a horizontal slider or single-hung is roughly half the frame width or height. A 600 mm-wide slider has only ~300 mm of operable sash — fails 380 mm. To pass with a slider you usually need a frame width of 1,200 mm or more.

What window-well rules apply to a basement bedroom?

Where the window opens into a window well, OBC 9.9.10.1.(3) requires at least 550 mm of clearance between the window and the opposite well wall. 9.9.10.1.(4) says the sash swing cannot reduce that clearance — outswing casements on tight wells often fail this. 9.9.10.1.(5) requires any cover/grate over the well to be openable from inside without keys, tools, or special knowledge. Wells over ~1,500 mm deep need a fixed climb-out ladder — that depth trigger is standard inspector (AHJ) practice, not a published OBC number.

Why are casements better for egress than awning windows?

Casement sash swings 90° and the entire rough opening is unobstructed — 100% of the dimensions count. Awning sash hangs at ~45° on a friction arm and stays in the exit path, cutting vertical clearance roughly in half. Many Ontario inspectors will not accept an awning as bedroom egress — verify with your AHJ before ordering.

Are bars or security grates allowed on bedroom egress windows?

Only with a quick-release that operates from inside without keys, tools, or special knowledge — same standard as 9.9.10.1.(5) for window-well covers. A keyed lock or any device requiring rummaging in a drawer during a smoke-fill fails the rule. Inspectors write up barred bedroom windows immediately, regardless of how good the dimensions are.

Do I need to replace existing windows when finishing a basement bedroom?

If the existing clear opening doesn't hit 0.35 m² with no dimension under 380 mm, yes. The most common renovation failure is a like-for-like replacement that drops the operable opening below 380 mm because the new vinyl frame is thicker than the old aluminum it replaced. Always size the replacement to the clear opening, not the rough opening.

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