- Underpinning extends an existing foundation downward with new footings poured underneath it, either to lower the basement or to stabilize walls that have settled.
- It's done in small, numbered sections dug in an order an engineer sets, so the house stays supported the whole time.
- In Ontario it needs a building permit, because it's a material alteration to the foundation of an existing building, and it's almost always designed from engineered drawings.
- Lowering a detached house typically costs $55,000 to $95,000 for the structural work, or $350 to $600 per linear foot, before waterproofing and finishing.
What is underpinning?
Underpinning is deepening an existing foundation by building new footings beneath it. The house stays where it is. Section by section, we dig below the old footing, pour new concrete underneath, and pack it tight to the wall above, until the whole wall sits on a new, deeper base.
Homeowners usually come to it for one of two reasons:
- Lowering the basement. Many older basements were built as cellars, with low ceilings and shallow footings. Underpinning lets you dig the floor down and gain real ceiling height without giving up any floor space.
- Stabilizing a foundation. When part of a house settles because the soil under a footing has moved, or was never compacted properly, new footings carried down to firmer ground stop it going any further.
Underpinning is also how a new below-grade entrance gets built when the opening has to go deeper than the existing footing. If settling is what brought you here, start with our guide to settling foundations.
Signs a house needs underpinning
- A basement ceiling too low to finish. The Building Code asks for 2,100 mm (about 6 feet 11 inches) over at least 75% of a basement, and many older basements fall well short.
- Plans for a legal secondary suite, a bedroom or a family room in the basement.
- Footings that are shallow, exposed, cracked or undermined.
- Cracks that are wider at the bottom than the top, doors and windows that stick, or floors that slope. Those are common signs of settlement.
- A walkout or new basement entrance that needs to go below the existing footing.
A crack on its own doesn't mean you need underpinning. Many are shrinkage cracks that only need sealing. The pattern, the width and whether it's moving tell you which.
How underpinning is done, step by step
- 01
Assessment and engineering
We check the existing footings, the soil and any neighbouring foundations. Then an engineer designs the new footings and sets the order the sections are dug in.
- 02
Permit
The drawings go to the municipality with the permit application. Nothing gets dug until the permit is issued.
- 03
Numbered sections
The wall is marked into small numbered sections, typically a few feet wide. They're dug and poured in the engineer's order, never side by side, so most of the wall is always sitting on solid ground.
- 04
Pour and pack
Each section gets new concrete under the old footing, dry-packed tight to the wall above, before the sections beside it are opened.
- 05
Floor, drainage and waterproofing
Once the walls are carried down, the floor is dug out, new weeping tile and a sump go in where they're needed, the walls are waterproofed while they're exposed, and the new slab is poured.
- 06
Inspections and sign-off
Inspections at the stages the permit requires, the engineer's review, and the permit closed with documentation you keep.
The sequence is what keeps the house safe. Opening more sections at once than the plan allows is a common shortcut, and a risky one. It's the first thing to ask any contractor about, including us.
Permits and engineering for underpinning in Ontario
Ontario's Building Code Act says no one can construct a building without a permit, and it defines construct to include the material alteration or repair of a building. Underpinning changes the foundation a house stands on, so it needs a permit and drawings.
Municipalities spell it out. Oakville and Mississauga both list underpinning foundation walls, and excavating to increase existing headroom, as work that needs a building permit. Toronto's residential underpinning guide goes further: an engineer has to design the work and review it on site when the new foundation goes below a neighbouring building's footing and within the soil's angle of repose (close enough that digging could undermine it), engineers' reports are needed at the first and last stages, and the plans have to show the sections numbered in the order they'll be built.
In Hamilton, Ancaster, Dundas, Stoney Creek and Waterdown, permits come from the City of Hamilton's Building Division. Starting early is expensive: the City's permit fee goes up by at least 25% if foundation work begins before the permit is issued. Lots near creeks or the escarpment can also need approval from a conservation authority or the Niagara Escarpment Commission.
Stamped drawings for underpinning typically run $1,500 to $5,000. We coordinate the engineer, the drawings and the permit as part of the job.
How much height can underpinning gain?
That depends on how deep the existing footings are, the soil, and what the space is for. Every inch comes from digging below the old footing, which is why the engineer looks at soil and footing depth first. In practice, the target is usually set by the Ontario Building Code.
| Space | Minimum ceiling height, 2024 Ontario Building Code |
|---|---|
| Basement space in a house | 2,100 mm (about 6 ft 11 in) over at least 75% of the basement area; 1,950 mm (about 6 ft 5 in) under beams and ducts |
| Secondary suite in a house | 1.95 m (about 6 ft 5 in); 1.85 m (about 6 ft 1 in) under beams and ducting |
| Bedrooms | 2,300 mm over at least 50% of the required floor area, or 2,100 mm over all of it |
Table 9.5.3.1 and Sentences 9.5.3.1(2) and (3) of the 2024 Ontario Building Code, in force since January 1, 2025. Your designer confirms what applies to your plans.
The 2024 Code is the first to put those secondary suite heights into Part 9. And remember the finishes: flooring, the ceiling itself and ductwork all take height, so we plan the finished ceiling first and work back to the dig depth.
A basement bedroom also needs a way out. Unless there's a door on that level leading directly outside, the Code calls for an outside window that opens to at least 0.35 m², with no dimension under 380 mm, and at least 550 mm of clear space in front of it if it opens into a window well.
What underpinning costs around Hamilton
Underpinning is priced mostly by the linear foot of wall. These are the things that move the number:
- How much depth you're gaining, and how deep the existing footings already are.
- Soil conditions and groundwater.
- Access for equipment and for hauling soil out.
- Neighbouring foundations close to the wall, which is common in semis and row houses.
- Whether waterproofing, drainage, a sump and a new slab are part of the job.
| Scope | Typical range |
|---|---|
| Underpinning, per linear foot of wall | $350 to $600 per linear foot |
| Detached house, structural work only | $55,000 to $95,000 |
| With waterproofing, drains and a new slab | $70,000 to $120,000 |
| Engineered drawings | $1,500 to $5,000 |
Typical Hamilton-area market ranges before tax, drawn from 2026 Ontario price guides and published contractor rates. Your number comes from a written quote after we've seen the house.
A bench footing is the cheaper way to lower a basement, typically $20,000 to $45,000, but it costs you floor space. Our guide to lowering a basement floor compares the two side by side.
How long it takes, and living at home during the work
Most residential underpinning takes several weeks on site, depending on the size of the basement and the soil. You'll get a schedule with your quote, with the permit's inspection stages built into it.
Most families stay in the house. The work happens below grade and the house stays supported throughout, but expect noise, dust in the basement, and a busy driveway while soil goes out and concrete comes in. Anything stored in the basement has to come out before we start.
Semis, row houses and century homes
Underpinning beside an attached neighbour takes more care. The new footing may go below the neighbour's, which is exactly the case where Toronto's guide requires an engineer to design and review the work. It's also worth talking to your neighbours before the job starts, so nobody is surprised by the excavation or the noise.
Older homes bring their own questions. Century houses like the ones in Dundas, Brantford and Galt can sit on stone or rubble foundations that were built for a cellar, not a full-height basement. Those walls can often be underpinned, but sometimes a section is better rebuilt. We'll tell you which after we've seen it, and put both options in writing if both make sense.
Underpinning questions
How much does it cost to underpin a house?
Is underpinning safe for the house?
Do I need a permit to underpin my foundation?
Underpinning or bench footing?
Can underpinning fix a settling foundation?
Our underpinning and basement work
Related guides
AVH Foundations works across Hamilton, Burlington, Oakville, Milton, Ancaster, Dundas, Stoney Creek, Waterdown, Cambridge, Brantford, Caledonia and Grimsby.