Project Case Study. Old Toronto east end. Pin-method basement underpinning, 24 inches of new headroom for a legal rental unit. Free on-site quote: 416-317-3090
Basement Underpinning Toronto — 24-Inch Drop on a Riverdale Semi
A Riverdale homeowner had a 6’2″ basement and a plan to legalize a rental suite. City of Toronto wants 6’5″ minimum, the bank wants 6’11”, the owner wanted real 8-foot ceilings. That meant dropping the floor 24 inches under a 1920s semi, with a shared party wall and a 32-inch side gate as the only way in. Pin-method underpinning, 10-12 working days. Free assessment: 416-317-3090.
Project Snapshot
- Location: Old Toronto east end, Riverdale / Leslieville area (neighborhood reference only)
- Job type: Pin-method basement underpinning, 24-inch floor drop, new slab, waterproofing tie-in
- Crew: 3-4 person, plus stamping structural engineer on inspection days
- Timeline: 10-12 working days on site, 5-6 weeks quote to start (engineering + permit)
- Equipment: Yanmar Vio17 (fits 32-inch side gate), Bobcat S70 for spoil, mini excavator for trench cuts, electric jackhammer, hydraulic breaker, hand dig in 3-foot sections
- Approximate cost: $32,000-$48,000 all-in (underpinning scope only)
- Permits: City of Toronto Building Permit, stamped structural drawings, party wall agreement
The Setup
1920s row-style semi-detached on a 20-foot lot. Basement ceiling was 6’2″ finished, 6’7″ to joists. Owner wanted a legal second-suite rental at real 8-foot ceilings, not a crawl-converted box. That meant 24 inches of new floor drop, plus slab.
Site was tight. Side passage front to back: 32 inches at the narrowest, between the house and the neighbour’s fence. The Yanmar Vio17 (28-inch retracted track) was the only machine that fit. Party wall on the east side was shared with the neighbour’s identical semi, original brick foundation, no daylight gap. That meant a party wall agreement signed before we touched the wall footing, and an engineer-staged pin sequence so we never undermined both halves at once.
The Plan
Two methods on the table. Bench footing keeps the existing foundation and pours a stepped concrete bench inside the perimeter. Cheaper, skips the party wall, half the time. We rejected it. The basement is 14 feet wide. A bench at 24 inches of drop eats roughly 32 inches off each wall, finished width down to 8 feet 8 inches. Legal ceiling, bowling-alley floor plan. Underpinning was the only honest answer.
Pin-method underpinning works the foundation in 3-foot sections. Dig under the existing footing, form, pour concrete, cure, move to the next non-adjacent pin. The sequence on this job: 14 pins around the perimeter, alternating so no two adjacent pins are open at the same time. Engineer required a 72-hour cure between adjacent pins. City of Toronto building permit was straightforward once the stamped drawings landed. The party wall agreement, signed and notarized with the adjoining owner, took longer than the permit itself.
The Execution
Day 1-2. Site setup, dust barriers at the top of the basement stairs, ductwork removed and stacked for the HVAC sub to reinstall later. Existing slab broken out with the electric jackhammer (no gas indoors), hauled in 5-gallon pails to the Bobcat in the back yard, Bobcat shuttled to a 14-yard dump trailer at the front. Slab gone by end of Day 2.
Day 3-9. Pin work. Each 3-foot pin: hand-dig under the footing to 24 inches below finished slab grade, place rebar cage tied to dowels drilled into the footing above, form, pour 25 MPa concrete, leave a 2-inch gap and dry-pack 24 hours later so the pin carries load. Alternating sequence, 3 per day, never adjacent. Vio17 ran spoil out the side gate. Engineer inspected at pin 4 and pin 10. Surprise at pin 4 on the party wall side: fieldstone foundation rubble below the poured footing. Common on pre-1920s east-end footings set on rubble fill. We called the engineer, redesigned that pin and the next two with a wider base to bear on undisturbed clay. Half-day added.
Day 10. Last pour, final cure. Perimeter of new underpinning visible as a continuous concrete bench at the base of the original foundation, 24 inches deeper than the old floor.
Day 11-12. Backfill interior over the new pins to slab subgrade. 6 inches of 19A clear stone, plate-compacted. 6-mil vapor barrier, taped at seams, turned up the walls. Tie existing weeping tile to the new perimeter at the base of the underpinning, interior weeper added where the original system did not exist (most 1920s semis did not have one). 4-inch poured slab with 10M rebar mat, troweled smooth. Engineer’s final inspection, letter issued, site swept.
The Result
Finished ceiling height slab to underside of joists: 8 feet 2 inches. Engineer’s letter in hand for the City of Toronto inspection and for the homeowner’s file when the second-suite permit closes out. New slab, vapor barrier, perimeter weeper tied to the existing exterior system, dry floor. Owner moved to framing the following week with a separate interior contractor.
Cost Breakdown
Rough ranges for a comparable east-end semi with a shared party wall and tight access. This job landed mid-range.
| Phase | Cost Range | Notes |
|---|---|---|
| Permits, engineering, party wall agreement | $3,500-$5,500 | Toronto permit, stamped drawings, neighbour consent |
| Slab demo, ductwork relocation | $2,800-$4,200 | Electric jackhammer indoors, pail haul |
| Underpinning pin work (14 pins) | $14,000-$21,000 | $1,000-$1,500 per pin: hand dig, form, rebar, 25 MPa pour, dry pack |
| Concrete, rebar, dowels, formwork | $3,200-$4,800 | Material only |
| New slab, vapor barrier, rebar mat | $3,800-$5,500 | 4-inch slab, 6-mil barrier, 10M mesh |
| Weeping tile tie-in, interior drainage | $2,400-$3,800 | Tie new perimeter to existing exterior weeper |
| Disposal, hauling, site protection | $2,300-$3,200 | Spoil + slab debris, dust barriers |
| All-in underpinning scope | $32,000-$48,000 | Excludes framing, drywall, electrical, plumbing, finishes |
What We Would Do Differently
Book a portable washroom on Day 1, not Day 4. Narrow east-end lot, no laneway, the side gate handles a Vio17 and a wheelbarrow, that is it. Crew walked to a Queen East coffee shop for three days because we assumed the homeowner’s washroom would be fair game on a 10-12 day occupied-home job. It was not. Half-hour loss per crew member per trip. Standing rule now: porta-john on the driveway Day 1 on any underpinning longer than a week.
Want a Similar Project Done?
OCM Excavation runs basement underpinning, bench footing, and foundation lowering across Toronto, East York, Scarborough, North York, and the rest of the GTA. Free on-site quote in 24-48 hours. Pin method, bench footing, party wall, tight-access semi, that is the conversation. Call 416-317-3090.