Basement Egress Window Installation: Building Code Requirements and Process

Basement Renovation Possibilities

An egress window is required for any basement bedroom — understanding what qualifies and how the installation works ensures Code compliance and legal habitable use.

Ontario Building Code defines minimum egress window requirements for sleeping rooms below grade: minimum opening area of 0.35 square metres, minimum opening height of 380 mm, minimum opening width of 380 mm, and maximum sill height of 1.0 metre above the finished floor. The window must be operable without tools or special knowledge.

Planning and Permits

Casement and awning windows provide the best egress opening area because the full sash area is available when the window is open. Double-hung windows only provide half the sash area as egress opening. Sliding windows provide the full height but half the width, which may or may not meet the minimum opening width depending on overall window size.

Window well installation is required when a new or enlarged basement window creates a below-grade opening. The well must provide a minimum 1.0-metre depth from the bottom of the window sill to the bottom of the well, and minimum interior dimensions sufficient for a person to stand and exit the window.

Making the Most of Your Space

Structural lintels are required above the new or enlarged window opening. When the opening is cut into the foundation wall, a concrete, steel, or precast lintel carries the load above the opening. Sizing the lintel correctly for the span and load above is a structural calculation — typically provided by the contractor or a structural engineer for larger openings.

Waterproofing at the new window opening is a critical detail. The transition between the window frame and the concrete or block foundation wall must be sealed with a waterproof flashing system. Improperly flashed basement windows are a common source of water infiltration.