What size does an egress window need to be under BC Building Code?

Under the BC Building Code, an egress window must have a minimum unobstructed opening of 0.35 square metres (3.77 square feet), a minimum opening width of 380 millimetres (15 inches), and a maximum sill height of 1,100 millimetres (43 inches) from the finished floor. All three requirements must be met simultaneously — a window that meets two out of three does not comply.

It is important to understand that "unobstructed opening" means the clear space when the window is fully open, not the overall frame size or the glass area. A window with a 24-by-36-inch frame may have a much smaller actual opening once you account for the sash, hardware, and opening mechanism. Casement windows and awning windows typically provide the largest unobstructed opening relative to their frame size, which is why they are the most commonly used styles for basement egress in Metro Vancouver. A slider window, by contrast, can only open half its frame width, so you need a significantly larger frame to achieve the same unobstructed opening.

For practical planning, most contractors in Metro Vancouver install egress windows with a rough opening of approximately 36 to 48 inches wide by 24 to 36 inches tall. This provides enough unobstructed opening to comfortably exceed the 0.35 square metre minimum while fitting standard window sizes available from BC suppliers. Going slightly larger than the minimum is wise — it makes the window easier to escape through in an emergency, simpler for firefighters to enter, and avoids borderline measurements that could fail inspection.

Measuring and Planning for Metro Vancouver Homes

The sill height requirement of 1,100 millimetres maximum is measured from the finished floor to the bottom of the window opening. In many older Metro Vancouver basements — particularly post-war homes across Burnaby, North Vancouver, and Coquitlam with 6 to 7-foot ceilings — existing windows are set high in the wall, often within 200 to 300 millimetres of the ceiling. These windows almost always exceed the maximum sill height, meaning the foundation opening must be cut downward to bring the sill within reach. Cutting down into a foundation wall is more complex than widening because it changes the load path, and in BC's seismic zone, the engineered header design must account for earthquake loading.

If your basement has been or will be underpinned, the relationship between floor height and window position changes. After lowering the floor, a window that was previously too high may now fall within the sill height requirement, potentially avoiding the need to enlarge the opening. This is worth discussing with your structural engineer during the underpinning design phase.

For secondary suites, municipalities across Metro Vancouver may impose additional requirements beyond the base BC Building Code minimums. The City of Vancouver, for example, has specific guidelines for secondary suite egress that may require windows meeting the same standards as above but also specify minimum window well dimensions and drainage. Always check with your local building department before ordering windows or cutting openings.

The cost to install an egress window in a Metro Vancouver basement typically runs $3,000 to $8,000 per window, depending on whether you are cutting a new opening or enlarging an existing one, the foundation type (poured concrete versus concrete block), the depth of the window well required, and drainage needs. Given Metro Vancouver's annual rainfall exceeding 1,200 millimetres, a properly drained window well with a gravel base and weeping tile connection is essential — not an optional upgrade. Budget for this as part of the egress window installation, not as a separate project.

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