Basement egress windows in Ontario: when you need one and what it involves

When a basement needs an egress window

Under Article 9.9.10.1 of the Ontario Building Code, as reproduced in the City of Markham's builder tip updated to the 2024 Code, every floor level that contains a bedroom needs at least one outside window that can serve as an emergency exit. The exception is when a door on the same floor level as the bedroom gives direct access to the exterior.

Oshawa's Basement Renovation Guide puts it simply: basements containing bedrooms require direct access to the exterior through a door, or an egress window. If your basement already has a walkout or a separate exterior door on that level, you may not need a new egress window. Your building department will confirm.

What the Building Code requires

The window must meet all of the following, according to the Code text in the Markham builder tip. The Ajax and Peterborough basement guides show the same sizes.

• Openable from the inside without tools
• An individual, unobstructed open portion of at least 0.35 square metres (3.8 square feet)
• No dimension of that opening less than 380 mm (15 inches)
• Stays open on its own without extra support
• For sliding windows, the size applies to the openable part only

Window well clearance

Most basement egress windows open into a window well. The Code, as quoted by Markham, requires a clearance of not less than 550 mm in front of the window. The Ajax guide shows this as 21-5/8 inches. If the sash swings into the well, it must not block the escape path.

If you put a cover over the well, it must be openable from the inside without keys, tools or special knowledge. Oshawa's guide also asks permit drawings to show how water trapped in a new window well will drain.

How high can the sill be?

The Code's 1,000 mm maximum sill height applies to bedroom egress windows above the basement, not to basement areas. That does not mean any height is fine in practice.

The Town of Ajax's Finished Basements guide recommends that basement escape window sills be no higher than 4'-11" above the floor, and that access be improved with something like built-in furniture below the window. A window that is hard to climb through is hard to escape through.

Choosing the right window type

Window style changes how much of the frame actually opens. Ajax's guide notes that for sliding windows, the open area is measured with one panel slid open, not with both panels removed. For casement, hopper and awning windows, the opening hardware must not reduce the required clear area.

Casement windows often give a larger clear opening for the same rough opening size, but check the actual clear opening on the product specifications, not just the frame size.

Do you need a permit?

Usually, yes, if you are making the opening bigger or cutting a new one. Several local municipalities list this work directly:

• Whitby lists structural alterations such as adding windows or doors (Building Permits)
• Pickering lists new windows or doors where there were none before (Building Permits)
• Scugog lists making a new entrance or a new window opening (Building Permits)
• Oshawa exempts only a window replaced within the existing rough stud opening (Basement Renovation Guide)
• Kawartha Lakes exempts window replacement only where no framing members are altered (Building, Septic and Renovations)

Other rules that can affect the design

Oshawa's guide says windows are not permitted in walls closer than 4'-0" to the property line unless protected with a 45-minute fire-resistance rating. Ajax asks for lintel sizes, unprotected opening calculations and a foundation lateral support calculation when a window is new or enlarged. Side yards in older neighbourhoods can be tight, so check this early.

Egress in a basement apartment

If the basement is, or will become, a separate unit, exits are reviewed as part of the suite design. The Province's guide to adding a second unit says a separate exit for the second unit is preferable. Where the exit from one unit leads through another unit, a second means of escape must be provided using a window that is large enough for a person to get through and easy to open without tools.

Suite layouts raise other questions too, such as shared stairs and fire separations. See our guide to legal basement apartments, and ask your building department which requirements apply to your house.

Keeping the window well dry

A bigger window means a bigger opening in the wall below grade, so drainage matters. A well should be drained so water does not pool against the glass, and the soil around it should slope away from the house. A clear cover can keep out snow and leaves, but it still has to open easily from inside. Check the well each spring and fall and clear out debris.

What drives the cost

RenoAssistance estimates the cost of installing a basement egress window at "about $2,400 and more" in its basement cost article (updated September 2024). That is a national figure and real costs vary a lot. The main cost drivers are:

• Cutting a poured concrete or block foundation, and the lintel needed above the new opening
• Excavation outside, including access for equipment and any landscaping or decks in the way
• The window itself and its clear opening size
• The window well, drainage and any cover
• Interior finishing around the new opening
• Engineering, drawings and permit fees where required

Plan your basement bedroom with Oakridge

At a free site meeting, Oakridge looks at your existing windows, the foundation and the outside grade, and explains what an egress window would involve for your layout. Call 289-731-2086 or request a free site meeting online.