Updated October 3, 2026 · DF Property Management
Why legal status matters
An unpermitted suite can still be rented, and the tenant is protected by the Residential Tenancies Act either way. But owners take on the risk: an insurer may refuse a claim after a fire, a fire inspection can order the unit vacated, and a buyer's lender may give no value to the suite at all. A legal second unit is safer, easier to insure, and worth more on sale.
Which rules apply: Fire Code or Building Code
Ontario has two routes, depending on when the suite was created.
| Suite created | Main rules | What it means |
|---|---|---|
| Existed on or before July 14, 1994 | Ontario Fire Code, Section 9.8 (two-unit residential occupancies) | Retrofit standards, inspected by the local fire service |
| Created after that | Ontario Building Code, through a building permit | Plans reviewed and inspected by the municipality's building department |
Most suites being legalized today fall under the Building Code. Since January 1, 2025, that means the 2024 Ontario Building Code. It includes compliance alternatives for creating a second unit in a house that has existed for at least five years, which are usually more forgiving than new-construction rules.
The permit process
- Check zoning — Ontario's additional residential unit rules permit a second unit in most houses on serviced urban lots, but confirm with the municipality.
- Get drawings — a floor plan of both units showing fire separations, exits, windows, mechanical and plumbing. Drawings for a two-unit house can often be prepared by the owner; many owners still hire a BCIN-qualified designer.
- Apply for the building permit — with your municipality: Toronto Building, or the building department in Mississauga, Brampton, Markham and elsewhere.
- Electrical permit — new wiring, panel upgrades and hard-wired alarms need an Electrical Safety Authority (ESA) permit and inspection, usually pulled by a licensed electrical contractor.
- Build and book inspections — framing, insulation, fire separation, plumbing and final.
- Final inspection and close the permit — keep the closed permit and ESA certificate with your property records.
Fire separation
Under the 2024 Building Code compliance alternatives for existing houses, separation between the units — and between each unit and any shared space — is usually achieved one of two ways:
- A continuous smoke-tight barrier of at least 15.9 mm Type X gypsum board (on both sides of walls; on the underside of floor-ceiling framing), or
- A fire separation with a fire-resistance rating of at least 30 minutes.
Regular drywall does not count. Doors in a smoke-tight barrier are generally solid-core wood at least 45 mm thick with a self-closer. Gaps around ducts, pipes and pot lights must be sealed. The furnace room is often the hardest part, where ductwork runs through the ceiling. If the building is sprinklered, the rules change.
Under the older Fire Code 9.8 route, a floor separation can be 30 minutes, or 15 minutes where smoke alarms are installed in every unit and interconnected.
Getting out: exits and egress windows
The basement unit needs a safe way out that doesn't run through the upper unit. Typical solutions:
- A separate entrance — a side door with stairs down, or a walk-out.
- A shared interior stair or corridor, separated from the upper unit by a smoke-tight barrier or fire separation.
- An exterior walk-up stair. Where it's the only exit, nearby windows in the upper unit may need protection, or a second means of escape is required.
Bedrooms without a door directly to the outside need an egress window that opens from inside without tools and gives an unobstructed opening of at least 0.35 m², with no dimension under 380 mm. If it opens into a window well, leave at least 550 mm of clearance in front of it. Some situations call for a larger "escape window" instead — check which applies to your design.
Ceiling height and room sizes
- Ceiling height: at least 1.95 m in a basement second unit, and at least 1.85 m under beams and ducts.
- Minimum room areas apply to living, kitchen and bedroom spaces, with reduced sizes for combined spaces and one-bedroom units.
- Natural light: windows are needed in living areas and bedrooms, with lower requirements for houses more than five years old.
Ceiling height is the most common deal-breaker in 1920s houses in the Danforth or the Junction. Lowering the floor (underpinning) is possible but costly, and needs an engineer.
Alarms
- Smoke alarms on every storey, in every bedroom, in hallways near bedrooms and in shared areas, interconnected — hard-wired or wireless — so one alarm sounds them all.
- Carbon monoxide alarms next to sleeping areas where the house has a fuel-burning appliance or an attached garage.
Heating, ventilation, plumbing and sound
- Shared furnace: in a house at least five years old, one forced-air system can usually serve both units if a duct-type smoke detector shuts off the system when it detects smoke. Otherwise, return air can't be shared.
- Ventilation: mechanical ventilation in line with the code.
- Plumbing: each unit needs a kitchen sink, a basin, a toilet and a tub or shower, access to laundry, and its own water shut-off valve.
- Sound: newer houses need an STC rating of at least 43 between units. Older houses aren't required to, but tenants will thank you.
Local differences
Some GTA municipalities run a separate second-unit registration or licensing process on top of the building permit. Markham, for example, registers basement apartments. Check before you rent.
After it's legal
Update your insurance to cover a two-unit rental. A unit first occupied as a residence after November 15, 2018 is generally exempt from the rent increase guideline — confirm how that applies to your property. And keep the Fire Code obligations going: alarm tests every year and at each new tenancy, with written records.
How we help
Our renovations team coordinates designers, trades, ESA and building inspections through to a closed permit, with photos at every stage. Once it's finished, tenant placement and residential management keep both units let and compliant.
General information, not legal advice. Building Code and Fire Code requirements depend on your house and your municipality; confirm with a qualified designer and your local building department before you start work.