A large basement window can still have a surprisingly small opening. Sliders only open partway across the frame, and hinges or hardware can take up escape space. Before ordering a bedroom window, check the manufacturer's clear-opening dimensions for that exact model, then check the route through the well outside.
The current Ontario numbers
Ontario's current Building Code adopts the National Building Code of Canada 2020 with Ontario amendments under O. Reg. 163/24. The City of Ottawa's current Building Code advisory for egress windows, reviewed under the 2024 Ontario code, summarizes a required egress opening as follows:
- At least 0.35 m² of individual unobstructed open area in the fully open position.
- No clear opening dimension less than 380 mm.
- Openable from inside without tools.
- Able to remain open without extra support.
- Clear travel through the window well, with the local reviewer confirming the applicable clearance and access details.
Area and minimum dimension apply together. An opening 300 mm high and 1,200 mm wide has 0.36 m² of area, but it fails the 380 mm minimum dimension.
Why window type changes the answer
| Window type | Useful feature | Common trap |
|---|---|---|
| Casement | Much of the frame can become clear opening | Hardware or sash may project into a tight well |
| Horizontal slider | Simple operation | Only part of the total frame opens |
| Awning | Good rain behaviour | Open sash can block the escape path in the well |
| Hopper | Compact ventilation | Often a poor clear opening and awkward escape path |
Measure with screens, guards, restrictors, and hardware considered in their normal installed condition. A removable screen may still need to be removable quickly from inside. A child-safety limiter on a required egress window needs an emergency-release arrangement that satisfies the applicable code.
The window well is part of the exit
The current Ottawa advisory calls for 550 mm clearance in front of the open window with continued egress out of the well, and says a well deeper than 1,000 mm needs a method to assist escape. Your municipality makes the project decision, so show the well width, depth, grade, cover, ladder or steps, and the sash swing on the permit drawing.
- The open sash must not consume the escape space.
- A well cover must be openable from inside without tools if it sits in the path.
- Keep snow, stored items, and shrubs clear of the escape route; check that gates on the route can be opened.
- The well should be protected from soil collapse and coordinated with foundation waterproofing.
- Drainage must send water somewhere lawful and useful, not directly toward the new opening.
Sill height, steps, and fall protection
Access to the opening matters. The Ottawa advisory explains the general sill-height rule and basement exceptions, including the possible use of fixed steps or built-ins. It also discusses guard or window-restrictor rules where an openable window is low inside and high above exterior grade. Do not solve egress by accidentally creating a fall hazard on the other side.
Show fixed access clearly in the design. Do not rely on a loose stool for required access. A built-in cabinet can work only when its height, depth, strength, and path are accepted. Include the access dimensions on the drawing.
Cutting the foundation is structural work
Enlarging a basement opening can require a building permit and structural design. The opening may need a lintel or other support, and the cut must avoid undermining the wall, footing, or adjacent openings. The City of Toronto lists new windows or doors where none existed before among work requiring a permit. Local rules determine your application.
Before excavation, request public utility locates and arrange private locates for owner-side services. Our Ontario One Call guide covers that step. Then coordinate excavation support, concrete cutting, lintel work, waterproofing, insulation, flashing, drainage, and interior finish as one detail. The finished opening needs both structural support and a reliable drainage detail.
A bedroom window is not the whole exit plan
Whether a particular room or floor needs an egress window depends on the building layout, exits, suite arrangement, fire separations, sprinklers, and other code provisions. A legal secondary suite adds more questions about unit exits, interconnected alarms, and fire safety. Use the secondary-suite guide as the next checklist, not as a substitute for a code designer.
The clean approach is simple: confirm the permit path, design the whole escape route, select an exact window model, put its clear-opening data on the drawing, and inspect before covering. Everyone using the room should know how the window opens and how to get out of the well.
Test the bedroom with the bed, desk and blinds in place
Start with the approved bedroom use and exact required opening. Then draw the bed frame, bedside tables, wardrobe, desk, chair and door swings to their actual footprints. Reserve the approach to the window and the space needed to operate its hardware. A clear room drawing can become a blocked room when a desk is added beneath the sill.
Bed to approach
Reach the required opening without shifting furniture.
Hands to hardware
Operate the latch, limiter and screen with the blind installed.
Through the opening
Preserve the approved unobstructed opening and access arrangement.
Out of the well
Check the open sash, cover and assisted exit detail, then keep the outside route clear.
A planning check, not a prescribed furniture clearance or a substitute for the approved egress design.
For a practical mock-up, mark the desk depth with tape and place the actual chair and monitor where they would sit. Open the window from the intended approach. If you have to lean over equipment or move the chair to reach the release, reconsider that furniture position before placing outlets. Do the same check with the bed made and curtains hanging.
Do not use a loose stool or movable storage as a substitute for required fixed access. Any built-in step or cabinet relied on by the design needs the accepted dimensions and support. Keep window-seat storage outside this decision until its effect on the opening is resolved.
Repeat the operation check at handover and after furniture changes. Outside, clear leaves, snow and stored items from the well and make sure its cover opens as intended. The window-well cover guide follows that final part of the route. Do not wait for an emergency to discover the garden planter has acquired a new parking place.