What is the minimum egress window size required for a basement bedroom in Ontario?

The Ontario Building Code requires a minimum unobstructed opening of 3.77 square feet (0.35 square metres) for basement bedroom egress windows, with a minimum opening dimension of 15 inches (380 mm) in any direction. This means the window must provide at least 3.77 square feet of clear, usable space when fully opened — large enough for an adult to climb through and for a firefighter in full gear to enter. These dimensions apply to the actual clear opening, not the frame size or glass area, which is a critical distinction when selecting your egress window.

To put these numbers into practical terms, an egress-compliant window opening must be at least 15 inches wide and approximately 36 inches tall (or any combination that equals 3.77 square feet with no dimension less than 15 inches). Common egress window configurations in GTA basements include a 36-inch wide by 24-inch tall casement that swings fully open to provide the required clear area, or a 48-inch wide by 24-inch tall horizontal slider where the sliding panel provides at least 3.77 square feet of unobstructed opening. The key is measuring the actual opening once the window is in the fully open position — not the rough opening in the wall, not the frame dimensions, and not the glass size.

Casement windows (which swing outward on hinges) are generally the best choice for basement egress because the entire sash opens, providing maximum clear area relative to the frame size. A casement window with a 36-by-24-inch sash provides approximately 6 square feet of clear opening — well above the 3.77 minimum. Horizontal slider windows can also meet egress requirements, but only the sliding panel provides the opening, so the window needs to be larger overall to compensate. A slider where only half the window opens needs to be roughly twice as wide as a casement to provide the same clear opening.

Awning windows (which hinge at the top and swing outward from the bottom) are generally NOT suitable for egress because the opening mechanism restricts the clear area, and the open sash creates a barrier that makes climbing through difficult. Similarly, small hopper windows that tilt inward at the top are almost never large enough for egress compliance.

Beyond the window dimensions, remember the sill height requirement: the bottom of the egress window opening cannot be more than 44 inches above the finished floor. In basements with low ceilings, this can create a conflict — the window needs to be positioned low enough on the wall for the sill height requirement, but high enough to be above grade or within a window well on the exterior. Your contractor and window installer will need to balance these requirements when planning the window placement.

The cost of egress-compliant basement windows themselves ranges from $400 to $1,200 per window depending on the size, type (casement vs. slider), frame material (vinyl, fibreglass, or wood), and energy efficiency rating. The installation cost — cutting the foundation wall, installing the lintel, setting the window, constructing the window well, waterproofing, and restoring the exterior grade — adds $2,500 to $7,000 per window in the GTA. When budgeting for a basement with two bedrooms, plan for two egress windows plus installation, totalling $6,000 to $16,000 for this component alone.

Always verify egress compliance with your contractor before the foundation is cut, and confirm the window manufacturer's clear opening specifications match Ontario Building Code requirements. The City of Toronto inspector will measure the actual opening during inspection — there's no room for approximation.