Underpinning and basement lowering in Hamilton.

What underpinning is, and when it's the right call

Underpinning means building new, deeper footings under your existing foundation walls. It's how an older house gets a basement deep enough to stand up in, and it's also how a footing that has settled or been undermined gets a solid base again.

If the goal is more headroom, there's a cheaper alternative called a bench footing, which leaves the old footing in place and steps the floor down inside it. It costs less, but it takes floor space around the edges of the room, roughly as wide as the drop is deep. Our guide to lowering a basement floor compares the two side by side.

How much ceiling height you need

The Ontario Building Code sets the targets. Under the 2024 Code, a basement space needs 2,100 mm (about 6 feet 11 inches) of ceiling height over at least 75% of its area, dropping to 1,950 mm under beams and ducts. A secondary suite in a house needs at least 1.95 m, and 1.85 m under beams and ducting.

If you're planning a legal basement apartment, add the other rules that come with it, like a bedroom egress window with at least 0.35 m² of clear opening and no dimension under 380 mm. We design the new floor height around the use you have in mind, not just around the minimum.

Permits, engineering and how the work is staged

Underpinning is structural work, and Ontario's Building Code Act requires a permit before construction, which it defines to include the material alteration of a building. Municipalities near Hamilton spell it out: Oakville and Mississauga both list underpinning foundation walls and excavating to increase basement headroom as permit work.

The work follows an engineer's plan. The walls are marked into small, numbered sections, and each one is dug, formed and poured before the sections beside it are opened, so the house is supported the whole time. On semis and row houses, adjacent footings need extra care, and Toronto, for example, requires a professional engineer to design and review the work when it goes below a neighbour's footing and within the soil's angle of repose.

What underpinning costs

Underpinning is priced by the linear foot of wall, typically $350 to $600 per linear foot for the structural work in this region. For a detached house that usually lands around $55,000 to $95,000, and closer to $70,000 to $120,000 once waterproofing, new drainage and a new slab are included. Engineering and drawings, the depth you're gaining, soil and access are what move the number. See our underpinning guide for the full breakdown.