Building a Legal Basement Apartment

Homes with basement apartments are popular with many homeowners due to the income potential.  However, creating a legal basement apartment isn’t as simple as finishing a basement for personal use.  And just because a home already has a basement apartment, it doesn’t mean it is a legal basement apartment.

By definition, a legal basement apartment means that the apartment complies with zoning by-laws, fire and building codes, the electrical code, and any other requirements of the municipality.

Here are some key elements to building up a legal basement apartment, or any other apartment unit, that we have discovered in the apartments we have built or retrofitted in the past few years.



Municipal governments regulate how land and buildings can be used, and what can be built.  Toronto allows basement apartments (Toronto calls them secondary suites), while some municipalities in the Greater Toronto Area do not.  Even if adding an apartment is legal, there may be other restrictions to consider, such as parking.


Building Code

The building code regulates the construction of buildings to ensure the health and safety of occupants. The building code dictates minimum room sizes, minimum ceiling height, as well a window sizes, entry doors and exits, and fire separation.



The building code specifies the minimum window sizes as a percentage of the room. Additionally, they must be able to open to provide natural ventilation. Bedrooms and living rooms require windows, other rooms may not.  Usually we find that basement windows need to be enlarged to comply with building code requirements.  If the window is facing the side of the house within four feet of the property line, enlarging it may not be permitted.



The apartment must have an exit directly to the exterior. Often this is through the side door of the home or a separate basement entrance.  A secondary exit may be required, which can be through a window. Again, this usually means enlarging an existing window.


Fire Separation

Fire separation is a key element in any multi-unit residential building, and an element the building inspector will carefully inspect during construction.  The goal is to contain the fire in the unit in which it started and give occupants of the entire building enough time to leave before the fire spreads.  Properly done, it also limits property damage, as the fire is contained within the unit in which it started .  In the case of a basement apartment, there must be a complete barrier between the basement unit and the main floor.  This can be achieved by using fire rated drywall, fire retardant insulation, and steel doors or fire rated wood doors.


Other Requirements

Electrical work must be inspected, and the unit must have smoke detectors.  Some municipalities will require these to be interconnected, which means that if the smoke detector activates in one unit, it beeps in all the units.  Carbon monoxide detectors may also be required.


What will it cost?

The cost will depend on the existing layout and conditions in the home, but also on the specific requirements of the municipality and the building inspector.  It could be thousands, it could be tens of thousands.  Each property should be assessed by a qualified designer or experienced contractor.