What is the minimum ceiling height for a legal basement apartment in Ontario?

The minimum ceiling height for a legal basement apartment (secondary suite) in Ontario is 6 feet 5 inches (1.95 metres) in existing homes, though the Ontario Building Code requires 6 feet 11 inches (2.1 metres) for new construction and strongly encourages it for secondary suites. This measurement applies to the finished ceiling height in all habitable rooms including bedrooms, living areas, kitchens, and dining areas — not just the average height, but the usable height throughout the room after drywall, flooring, and any ceiling treatment are installed.

Understanding how this measurement works in practice is critical before you budget for a basement apartment project. The 6 feet 5 inch minimum is measured from the finished floor to the finished ceiling, and it must be maintained across at least 75% of the room's floor area. However, obstructions like beams, bulkheads hiding ductwork, support posts, and plumbing runs can reduce the effective ceiling height in specific areas. The Ontario Building Code allows these obstructions to project below the minimum height, but they must not reduce headroom below 6 feet 2 inches (1.88 metres) in areas where people regularly walk, and the reduced-height areas count against your 75% threshold. In many post-war GTA homes — particularly the bungalows and split-levels built between 1945 and 1975 across Scarborough, North York, Etobicoke, and the inner suburbs — the existing unfinished ceiling height is often only 6 feet 6 inches to 7 feet, which means after you add a finished floor (typically 1 to 2 inches for subfloor and LVP) and a finished ceiling (at least half an inch for drywall), you may be right at or even below the minimum.

This is where careful planning becomes essential. If your existing basement does not meet the minimum height after accounting for finished floor and ceiling, you have two options: lowering the floor (which involves breaking out the existing concrete slab, excavating, installing new drainage and a vapour barrier, and pouring a new slab) or underpinning (which involves excavating beneath the existing footings and extending the foundation deeper). Both are major structural projects. Underpinning is the more common approach in the GTA and typically costs $50 to $120 per square foot of basement floor area, meaning a typical 800-square-foot basement runs $40,000 to $100,000+ just for the underpinning work, before any finishing begins. A structural engineer's design is required for underpinning, adding another $3,000 to $6,000 for the engineering fees.

For the bathroom within the suite, the Ontario Building Code allows a slightly reduced ceiling height of 6 feet 2 inches (1.88 metres) over fixtures, which gives you a bit more flexibility in positioning the bathroom under lower areas like duct runs or beams. Hallways and utility areas also have some flexibility, but bedrooms, the kitchen, and the living room must all meet the full minimum.

Before committing to a basement apartment project, have a contractor or building consultant measure the clear height at the lowest points — typically at the main beam, at HVAC duct runs, and at any plumbing drain lines. These measurements, taken after accounting for finished floor and ceiling thickness, will tell you whether your basement can meet the minimum height as-is or whether structural work is needed. Many GTA homeowners are surprised to discover that what appears to be a tall enough basement actually falls short once you account for the finishes, and discovering this mid-project is far more expensive than measuring carefully upfront.