Many homeowners finish basements expecting them to function as rental units or in-law suites. However, a finished basement is not automatically a legal dwelling unit.
In Ontario, a legal basement apartment is referred to as a Secondary Suite, and it must meet specific Building Code and permit requirements.
What Is a Secondary Suite?
A Secondary Suite is a self-contained dwelling unit within a house that includes:
- A kitchen
- A bathroom
- Sleeping and living space
A Secondary Suite is only legal once it has been permitted, inspected, and approved.
Permits Are Mandatory
Creating a Secondary Suite always requires a building permit.
This is because:
- The number of dwelling units changes
- Fire and life-safety provisions apply
- Plumbing, heating, and electrical systems are affected
Unpermitted suites are one of the most common inspection and resale problems.
2024 Ontario Building Code Update — Smoke-Tight Separation
Under the 2024 Ontario Building Code, the separation between the main dwelling unit and the Secondary Suite no longer requires a fire-resistance rating by default.
Instead, the Code requires a continuous smoke-tight barrier between the units.
This barrier typically consists of:
- 5/8″ Type X gypsum board
- Installed on both sides of separating walls
- Installed on the underside of separating floor assemblies
- Continuous and sealed at all penetrations
The focus is smoke containment and early warning, not fire endurance time.
Temperature Control Requirement
Independent temperature control is typically required for the Secondary Suite, although acceptable methods depend on system design and Code compliance.
Other Common Requirements
A legal Secondary Suite must also meet requirements for:
- Minimum ceiling heights
- Proper exits and egress windows
- Smoke and carbon monoxide alarms
- Plumbing venting and shut-offs
- Heating and ventilation distribution
Why Secondary Suites Fail Approval
Common issues include:
- Missing permits
- Gaps in smoke-tight separation
- Inadequate ceiling height
- Improper egress windows
- Shared or interconnected ductwork
Most of these issues are preventable with early planning.
Key Takeaway
A finished basement is not a legal Secondary Suite unless it complies with current Building Code requirements and has passed inspection.
Building it right the first time avoids costly corrections later.
Disclaimer: This article is for general educational purposes only. Building Code interpretation and enforcement may vary by municipality. Always confirm requirements with your local Authority Having Jurisdiction.