Legal Basement Apartment / Secondary Suite in Ontario: Cost & Rules

A legal basement apartment — a "secondary suite" or "second unit" — can add rental income or space for family, and Ontario has broadly moved to allow them in most homes as part of the push for more housing. But "allowed in principle" is not the same as "legal in practice." Making a suite legal means meeting the Ontario Building Code and your municipality's zoning rules, and pulling a permit. This guide explains the framework; the specifics are set locally and change, so verify before you build.

Allowed in principle, legal in practice

Ontario planning rules generally require municipalities to permit an additional residential unit in many homes, and recent provincial changes have pushed to allow more units on a typical residential lot. What that means for you still depends on your municipality's zoning by-law — lot and unit requirements, parking, and whether your specific property and street qualify. The province sets the direction; your municipality sets the details. Start by confirming what your zoning actually allows on your lot.

What makes a basement suite legal

A legal secondary suite has to be a safe, self-contained dwelling that meets the Ontario Building Code (or the Fire Code framework that applies to certain existing units). The exact requirements are technical and change, but the recurring themes are safety and separation:

• Egress — a code-compliant way out, typically including a large enough egress window or a proper exit from the bedroom and unit.
• Ceiling height — a minimum clear height for habitable basement space (existing-home and new-build minimums differ; verify the current Building Code figure).
• Fire separation — a rated separation between the units, and interconnected smoke and carbon-monoxide alarms.
• A separate entrance — many municipalities require an independent entrance to the unit.
• Self-contained facilities — its own kitchen, bathroom, and living/sleeping space.
• Parking and zoning compliance — whatever your municipal zoning by-law requires for a second unit.
• Registration — some municipalities require second units to be registered.
• Permits and inspections — a building permit, and any electrical (ECRA/ESA) and plumbing work done to code and inspected.

What it costs (illustrative)

A legal basement apartment is a full basement finish plus a second kitchen, a bathroom (often needing a sewage ejector below grade), fire-separation work, egress, and the permit process — so it sits at the higher end of basement projects. As a rough, illustrative 2026 planning range, budget well into the tens of thousands, with the exact figure driven by drainage, egress, fire separation, and finishes. For the sequence and general basement cost drivers, see our basement finishing guides. Treat any number as a planning range, not a quote.