Escape routes from basements that include a bedroom.

In the design of a basement, there can be a need to include a bedroom.  The Ontario Building Code (OBC) in that case, requires a second means of exit, or egress, from such a basement.  There is more than one way to accomplish a second exit, but the most common method is called “egress window”.  The window is typically larger than most ordinary basement windows and therefore has minimum clear unobstructed opening requirements.

Clear opening in a window of the slider type.

The Ontario Building Code requires that the second exit have the following attributes:

1)  There must be no dimension smaller than 380mm (15″) and

2) the area of the opening must be no less than 0.35 sq. m (534 sq in.)

The definition of “clear opening” is an opening, clear of any obstruction, such as trim, stops or weather stripping including, in the case of a sliding window the opening cannot include the adjacent sliding window panel (see the diagram above.)

A simple formula for determining a compliant design is (window opening length) x (window opening height) must be equal to or greater than 0.35 sq. m.  and neither the length or width may be less than 380mm.

Once the window design is compliant, the space outside of the window must also be considered in the design of the exit path.  Included below is a clip from the appendix to the Ontario Building Code that illustrates acceptable exit spaces outside the egress window if the window looks out into a window well.

While the code requires 550mm of clear space, I generally design the clear space at 1m and never make an outward awning.  If possible the inclusion on a counter or cabinet below the window to assist in reaching the sill is a good idea.

Egress window well minimum dimensions

Note also that the bottom of the window well must be designed so that it is drained to the foundation weeping tiles but not connected to them.