# How Is a House Underpinned? The Concrete Underpinning Process, Step by Step

> Underpinning deepens a foundation in small, alternating sections called pins. An engineer designs the sequence and the City issues a permit. The crew then digs and pours one pin at a time, never two neighbours together, so the house stays supported. When all pins have cured, the floor is lowered and a new slab is poured. Expect 4 to 8 weeks of planning and 8 to 16 weeks of work.

*Category: underpinning | 7 min read | Updated 2026-11-12*

## The short version

Underpinning does not lift the house or pour a new foundation in one go. The existing footing stays where it is, and the crew extends the foundation downward underneath it, a small section at a time. That is what makes it safe: at any moment most of the wall is still sitting on the old footing, and only one short section is being worked on.

The method most Toronto houses use is traditional mass-concrete underpinning, also called the pit method. The steps below follow how a typical project runs, from the first site visit to the final inspection.

## Step 1: Site review and engineering

Before anything is dug, a structural engineer inspects the house and tests the soil. They record the depth and width of the existing footing, the condition of the walls and the type of soil, which in much of the GTA is clay. The engineer then stamps drawings that show the new depth, the size of each pin and the exact order in which the pins will be poured. Engineering and drawings typically cost $3,000 to $6,000.

## Step 2: Permit and notice

The drawings go to the City with a building permit application. Underpinning always needs a permit, and processing plus engineering usually takes 4 to 8 weeks. If you share a wall with a neighbour, they are notified in writing. Permit fees are billed at cost on top of the quoted price, either as a separate line or invoiced once the amount is known.

## Step 3: Prepare the basement

The crew clears the space, protects utilities, and sets up access for removing soil. In most Toronto houses that means a small opening, a chute or a conveyor to a bin outside, since there is no room for machines. Temporary shoring goes in where the drawings call for it, for example around a chimney base or a load-bearing wall.

## Step 4: Dig and pour the pins, one at a time

This is the core of the job. The drawings divide the walls into numbered sections. The crew digs the first section by hand beneath the old footing to the new depth, sets rebar, forms it and pours concrete. The gap between the top of the new pin and the underside of the old footing is packed with a stiff dry mix so the wall bears fully on the new concrete.

1. Dig pin 1, form and pour. Leave it to cure.
2. Move to pin 4, a few sections away, and repeat.
3. Continue around the walls following the engineer's sequence.
4. Return to the first pass of pins and dig the sections between them once the neighbouring concrete has cured.

> Two pins that sit side by side are never open at the same time. That one rule is what keeps the wall supported while the foundation goes deeper.

## Step 5: Lower the floor and add drainage

After every pin has cured and passed inspection, the crew excavates the rest of the floor to the new level. This is the best time to add waterproofing, weeping tile and a sump if the engineer or contractor recommends it, because the walls are open and the work shares the same excavation. A full waterproofing scope on an underpinning job typically adds $6,000 to $15,000.

## Step 6: New slab and inspections

Gravel, a vapour barrier and in many cases insulation go down, then a new concrete slab is poured, typically $3,000 to $7,000. The City inspects at set stages and the engineer reviews the work, so the sign-off is documented for future buyers and insurers.

## How long it takes and what it costs

| Stage | Typical time | Typical cost |
| --- | --- | --- |
| Engineering and drawings | 2–4 weeks | $3,000 – $6,000 |
| Permit processing | 2–4 weeks | Billed at cost |
| Pin-by-pin underpinning | 8–16 weeks for the active phase | $35,000 – $140,000 for the structural phase |
| Waterproofing (recommended) | Within the active phase | $6,000 – $15,000 |
| New floor slab | A few days | $3,000 – $7,000 |

A typical full-basement job in a detached house runs about $55,000 to $100,000+. All prices are before HST, which is 13% on the whole pre-tax amount.

## What homeowners should expect during the work

- Noise and dust from breaking out the floor and moving soil, usually on weekdays from morning.
- Soil bins at the curb, often for weeks, so check street parking and bin rules.
- Hairline cracks in plaster or drywall upstairs are common, so photograph the house beforehand.
- Inspections that pause the work. The pour waits until the inspector has signed off.
- Winter is a normal time for the interior work, since the digging is inside the basement. Exterior waterproofing slows when the ground is frozen.

## FAQs about how underpinning works

**Q: Is the house lifted during underpinning?**

No. The house stays on its existing footing while the new concrete is built beneath it in small sections.

**Q: Can I stay in the house during underpinning?**

Many owners do, since the work is in the basement, but expect noise, dust and restricted access. Larger or deeper jobs are often easier to live through if you move out.

**Q: Why can't the whole wall be done at once?**

Removing the soil under a whole wall would leave it unsupported. Alternating small pins keep most of the wall resting on the old footing at all times.

**Q: What is the difference between underpinning and bench footing?**

Underpinning extends the footings deeper and gives full floor area. Bench footing leaves the footing alone and lowers the central floor, which costs less but takes some floor width along the walls.

**Q: Do I need an engineer?**

Yes. Underpinning requires stamped drawings from a structural engineer, and the City will not issue a permit without them.

## Planning to lower your basement?

We start with a site visit, measure the footing and walk you through the engineering, permit and schedule, so you know what happens each week. Written, itemized scope, $0 down. Call (647) 254-0877.

## Related Services
- [Underpinning Services](https://buildoreno.ca/underpinning)
- [Basement Lowering](https://buildoreno.ca/underpinning/basement-lowering)
- [Underpinning Cost Guide](https://buildoreno.ca/underpinning-cost-toronto)
- [Basement Waterproofing](https://buildoreno.ca/underpinning/waterproofing)

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