The two budgets: with underpinning and without
Every basement apartment quote in Toronto splits into two very different projects, and the dividing line is ceiling height. The Ontario Building Code allows a secondary suite in an existing house with 1.95 m (6'5") of clear height in habitable rooms and 1.85 m under beams and ducts. If your basement already clears that, you are building a finished rental unit. If it doesn't — and most Toronto houses built before 1980 don't — you are first doing structural work to lower the floor, and only then building the unit.
| Scenario | What it includes | Typical 2026 cost |
|---|---|---|
| Finish-only conversion | Egress, fire separation, alarms, kitchen, bathroom, HVAC, permits, finishing | $50,000–$100,000 |
| Underpin + convert | Everything above plus structural underpinning or bench footing and waterproofing | $80,000–$180,000 |
| Underpin + walkout + convert | Everything above plus a new exterior stairwell entrance | $105,000–$225,000 |
Those are complete-project ranges from recent GTA work, not the "starting at" figures that get a contractor through the door. The rest of this guide breaks each one into its line items so you can see where your own house will fall.
Line item 1: underpinning or bench footing ($35,000–$140,000)
Underpinning digs beneath the existing footings in short sections and pours new, deeper concrete footings, then lowers the slab. It is the only method that keeps your full floor area and gets you to an 8–9 ft ceiling. The structural phase alone runs $35,000–$140,000 depending on basement size, how far you lower (2–3 ft is typical), soil and access. A 1,000–1,500 sq ft basement lowered 2 ft usually lands at $55,000–$85,000, including engineering, permits and inspections.
Bench footing is the cheaper alternative: instead of going under the footings, a sloped concrete bench is poured against them and the middle of the floor is lowered. You lose 12–24 inches of floor width along each exterior wall, which is why it suits wide basements and not narrow semis. Expect roughly 30–40% less than underpinning for the same depth.
The lowering decision is made once, for the life of the house. If the numbers are close, underpin — a bench along every wall permanently narrows a rental unit's bedrooms and makes the apartment harder to lay out and to rent.
Line item 2: the separate entrance ($3,000–$45,000)
A legal suite needs its own entrance. If your house already has a side door that opens onto a stair down, the fix can be as little as a fire-rated door and a small vestibule ($3,000–$8,000). If it doesn't, the standard solution in Toronto is a basement walkout: excavate beside the foundation, cut a door opening through the wall, build an engineered concrete stairwell with drainage and a landing. That runs $25,000–$45,000 and is almost always done in the same mobilization as underpinning, because the excavator and the structural engineer are already on site.
Line item 3: egress windows ($2,500–$5,500 each)
Every bedroom in the apartment needs an egress window with at least 0.35 m² of clear opening and no dimension under 380 mm, openable from inside without tools. In a typical Toronto basement that means cutting a larger opening, excavating a window well outside with a drain, and installing the window. Budget $2,500–$5,500 per bedroom. Two-bedroom suites therefore carry $5,000–$11,000 here before any finishing.
Line item 4: fire separation, alarms and HVAC ($9,000–$25,000)
- Fire-rated ceiling and separation wall assemblies, fire-rated door at the common area: $4,000–$12,000 depending on basement size and how much existing ceiling must come down.
- Interconnected, hardwired smoke and carbon monoxide alarms on every level, both units: $1,200–$2,500.
- HVAC: either a dedicated ductless heat pump for the suite ($4,500–$8,500) or re-ducting with return air and a fire damper on the shared system ($2,500–$6,000).
- Electrical rough-in and a sub-panel for the suite: $5,500–$12,000.
Line item 5: the finished suite ($25,000–$55,000 and up)
This is the part that looks like a normal basement renovation — framing, insulation, drywall, flooring, paint, trim — plus a full kitchen and bathroom and the plumbing rough-in they need. Interior finishing for a modest one-bedroom runs $25,000–$55,000. Measured per square foot, a code-compliant rental suite costs $110–$200, against $60–$90 for a basic rec-room finish, because of the kitchen, the second bathroom and the fire-rated assemblies.
| Component | Typical 2026 range (GTA) |
|---|---|
| Underpinning (structural phase) | $35,000–$140,000 |
| Bench footing (alternative) | $25,000–$90,000 |
| Basement walkout entrance | $25,000–$45,000 |
| Egress window + well (per bedroom) | $2,500–$5,500 |
| Fire separation assemblies | $4,000–$12,000 |
| Interconnected smoke / CO alarms | $1,200–$2,500 |
| HVAC for the suite | $2,500–$8,500 |
| Electrical + sub-panel | $5,500–$12,000 |
| Kitchen, bathroom, plumbing rough-in | $18,000–$40,000 |
| Framing, drywall, flooring, paint | $25,000–$55,000 |
| Engineering, drawings, permits | $4,000–$9,000 |
What the apartment earns back
A finished one- or two-bedroom basement unit rents for $1,800–$2,800 a month across most of the GTA in 2026, or $21,600–$33,600 a year gross. Against a $120,000 all-in conversion that is a 4–7 year payback before you count the resale uplift — legal suites typically add more to the sale price than they cost to build, because buyers underwrite the rent. An unregistered unit earns none of that: it cannot be advertised as legal, it voids most home-insurance policies, and it is a liability at resale.
Five things that move the price
- 1Existing ceiling height. Every inch below 1.95 m means underpinning or benching — the single largest swing in the whole budget.
- 2How far you lower. 2 ft is standard; a third foot adds 20–30% to the structural phase.
- 3Access. A detached house with side-yard access for a mini-excavator is cheaper than a mid-row semi where spoil leaves by conveyor through the front.
- 4Water. A basement that already leaks needs waterproofing and drainage done at the same time ($4,000–$15,000 on top), but it is far cheaper while the floor is open.
- 5Number of bedrooms. Each one adds an egress window and well.
Owner-Operator at Buildoreno with 25+ years of hands-on GTA construction experience. Last reviewed October 2026.