What makes a basement apartment legal in Toronto?

Four things decide it: ceiling height, an egress window in every bedroom, a rated fire separation between the units and the shared exit, and smoke and carbon monoxide alarms interconnected through the whole house. Electrical work has to be inspected and approved by the Electrical Safety Authority.

Zoning adds its own limits. One secondary suite per dwelling unit, and the suite cannot exceed 45 percent of the home's interior floor area, except that a one-storey detached house may use the whole basement. No extra parking space is required.