Basement Permits

Basement Apartments in Ontario: What the Permit Process Actually Involves

📅 Published by GranDesign Engineering 🔎 Structural Engineering & Building Permits

Adding a legal basement apartment — also called a secondary unit or second dwelling unit — is one of the most practical ways to add rental income or family housing to an existing home. But the permit process is more involved than many homeowners expect.

Why You Need a Permit

Ontario law requires a building permit for any basement apartment. An unpermitted unit creates serious liability — it cannot legally be rented, affects your insurance, and may need to be removed if discovered during a home sale or inspection.

A permitted basement apartment, on the other hand, is a legal asset that adds measurable value to your property.

What the Permit Covers

A basement secondary unit permit application typically requires drawings and compliance documentation for:

Fire separation — a minimum 30-minute fire-rated assembly between the unit and the rest of the house
Egress — a window or door that meets minimum size requirements for emergency escape
Structural modifications — any walls moved, beams added, or openings created must be shown in P.Eng-stamped drawings
Separate entrance — if a separate entrance is added or modified, it requires its own structural and architectural details
HVAC and plumbing — the unit needs its own heating and ventilation, and any new plumbing must be permitted

Our role: We prepare the structural component of the permit package — P.Eng-stamped drawings for any structural modifications, beam work, and load path changes involved in creating the unit. For a complete application, you may also work with a designer or architect for the architectural drawings.