Ontario ADU & Basement Apartments

Nick Nobel

Sep 15

4 min read

Updated: Sep 24

Basic requirements for basement apartments & ADUs in Ontario

Can I put an apartment in my house?

In short – probably! Due to the strain on housing, rising house prices, and increase in immigration to southern Ontario, the provincial government has pushed for more housing and almost all townships now allow at least one secondary dwelling on most residential properties, and some townships allow up to three. This includes basement apartments, attached main floor or second floor units, or detached units.

Zoning By-laws (Township’s rules)

A secondary apartment on your property can go by many different names, ADU (accessory dwelling unit), ARU (accessory residential unit), Basement Apartment, Garden Suite, and more but they all mean the same thing – a second dwelling unit that is subsidiary to the main dwelling unit on a single residential property.

Every township, county, or city has their own set of rules, called zoning by-laws, that specify what type of property can have what type of building. They all have different rules for how large, how close to property lines, the location, and the use of these buildings. The following are TYPICAL requirements across Ontario. Please look into your specific zoning by-laws for accurate rules in your area.

Zoning Rule	Typical requirements (not specific to your township)
Size	Usually up to 40-50% of primary dwelling, up to 1000-1500sf
Location	Not typically allowed in front yard Often allowed very close to side & rear property lines Keep in mind – closer to property line means less windows & more fire separation rules
Height	Typically must ber shorter than main dwelling Up to max. 15’-20’ (measured to mid-point of a sloped roof)
Access	3’-4’ unobstructed walkway from front of house
Parking	1-2 spots for main unit, 1 additional spot for apartment. Garage counts toward parking

If your proposal does not meet the zoning requirments but you still want to build it, you can apply for a Minor Variance in most areas to request specific approval for your change.

Here are some local ADU requirements:

Some townships have put together helpful ADU guides. Please note, these documents may be out of date due to zoning changes. Always check with your local building or planning department.

Building Code (Province’s rules)

**New home less than 5 years old require a completely separate furnace/heating system for an attached apartment**

Once you determine if you are allowed to put in an ADU, now you need to comply with the egress, fire safety, and minimum standards of the Ontario Building Code. I am going to focus on basement apartments, as these usually have the most stringent rules, but these rules apply to all ADU’s.

Code Rule	Houses less than 5 years old	Houses more than 5 years old
Ceiling Height (basement apartments)	6’-5” (6’-1” below bulkheads)
Fire Separations	5/8” Type ‘X’ smoke-proof barrier on walls & ceiling	Existing ½” ceiling may be acceptable
Sound Barrier	2 layers 5/8" drywall with resilient channel & Roxul insulation	Existing ceiling may be acceptable (although not always recommended)
Heating & cooling	No shared furnace permitted Apartment requires seperate heating & ventilation (ERV)	Shared furnace with in-duct smoke detector acceptable
CO & Smoke Alarm	Hardwired & interconnected with primary dwelling unit (if attached). Each bedroom & each floor.
Egress	EGRESS window required when exit door does not exit directly to exterior (exit through basement stairs) ESCAPE window required when apartment exits through shared space (exit through garage)
Required Appliances	Bathroom: toilet, sink, & tub/shower Kitchen: sink, fridge, & space for cooktop Washer & Dryer hookup or shared laundry with main unit

Escape & Egress window requirements:

There is no egress or escape window required if the dwelling unit has a door on the same level that leads directly to the exterior.

Window Type	Min. Width /Height	Min. Area	Max. Sill Height	Location
Egress Window	15”	3.8sf	N/A	Required as secondary egress from basement with no walk-out exit
Escape Window	18”	4.1sf	2'-11" above floor 3'-3" below grade	Required as secondary egress when apartment’s primary exit leads through shared space (exit through garage)

Room sizes:

Individual Room Dimensions:

Room type	Minimum room size (measured to the inside face of walls)	Minimum window glass area, in houses less than 5 years old	Minimum window glass area, in houses more than 5 years old
Living room	145sf	14.5 square feet (10%)	7.25 square feet (5%)
Dining room	75sf	7.5 square feet (10%)	3.75 square feet (5%)
Kitchen	One bedroom: 40sf Two bedrooms: 45sf	Windows not required	Windows not required
Master bedroom	With closet: 95sf (not including closet) Without closet: 105sf	5 square feet (5%)	2.5 square feet(2.5%)
Second bedroom	With closet: 65sf (not including closet) Without closet: 75sf	3.75 square feet (5%)	1.9 square feet (2.5%)
Bathroom/utility room	No minimum (bathroom must be functional and usable)	Windows not required	Windows not required

Combination Rooms (Open Concept Primary Rooms, Not Including Bathrooms)

Number of bedrooms in apartment	Room size (minimum, measured to the inside face of walls)	Minimum window glass area in houses less than 5 years old	Minimum window glass area in houses more than 5 years old
Two bedrooms	Living room + dining room + kitchen: 225sf Living room only: 180sf	18 square feet (10%)	9 square feet (5%)
One bedroom	Living room + dining room + kitchen: 193sf Living room only: 153sf	15 square feet (10%)	7.5 square feet (5%)
Bachelor apartment	Living room + dining room + kitchen + bedroom: 145sf	14.5 square feet (10%)	7.25 square feet (5%)

There are many specific rules and nuances of the building code that apply differently to older vs. new houses. Other considerations like septic systems, wells, or old services may impact your ability to construct a new dwelling unit without massive costs.

Reach out today to discuss your ADU or apartment and see what will work for you!