A rear single-storey addition in Toronto runs $450 to $650 per square foot in 2026. A second-storey addition over an existing footprint runs $550 to $750 per square foot. A 400 sq ft kitchen and family-room extension is therefore a $180,000 to $260,000 project. A 700 sq ft second-storey addition adding three bedrooms and a bath is $385,000 to $525,000.
Those numbers assume a permit-ready design, a typical Toronto lot, no Heritage Conservation District constraint, and no Committee of Adjustment hearing. Layer in any of those and the timeline (and sometimes the cost) move materially.
Why the per-square-foot number is so high
A new bedroom in a finished basement costs $80 to $150 per square foot. A new bedroom in a second-storey addition costs $600 per square foot. The additional $450 buys you these things, all of which the basement room already has:
- Foundation. A new addition needs new footings, frost protection (4 feet below grade in Toronto), and either a poured wall or a slab on grade. Add $35 to $70 per sq ft of footprint.
- Roof. New trusses, sheathing, ice and water shield, underlayment, shingles or membrane, and tie-in to the existing roof. Add $40 to $70 per sq ft.
- Exterior envelope. New siding or cladding, windows, doors, weather barrier, insulation, sheathing. Add $80 to $140 per sq ft of wall area, which on a typical addition is $40 to $60 per sq ft of floor area.
- Mechanical extension. Furnace and AC capacity check, possible new equipment, ductwork extension, plumbing extension, electrical extension. Add $25 to $50 per sq ft.
- Connection cost. Demolishing the existing wall, beaming over the opening, patching the floor and ceiling above, matching the existing finishes. Add $15,000 to $40,000 lump sum, not per sq ft.
A second-storey addition skips the foundation cost but adds structural reinforcement to the existing first-floor walls and footings (because the existing house was not designed to carry a second storey), plus the engineering and shoring required to build above an occupied house. That is the $100 per sq ft difference between rear and second-storey.
Committee of Adjustment, the silent timeline killer
Most Toronto additions exceed the as-of-right zoning bylaw on at least one metric — usually rear yard setback, lot coverage, FSI, or building height. Any one variance triggers a Committee of Adjustment hearing.
The hearing process runs 4 to 6 months from application to decision in 2026. Your neighbours are notified, can object, and the Committee can refuse, defer, or approve with conditions. We have had additions approved in the first hearing, deferred for a re-design, and refused outright. The wait is real and the budget needs to absorb it.
We assess variance risk in the first design meeting. If your rear yard setback is fine and your FSI is fine, you can permit and start in 8 to 12 weeks. If you need a Committee hearing, plan on a year from initial design to first day on site. That is not the contractor's pace — it is the City's.
For more on how we work in the city, see our Toronto location page. For the additions service overview, see home additions. For Toronto-specific zoning, Committee of Adjustment notes, and neighbourhood precedents, see our home addition in Toronto landing page.
Heritage Conservation Districts
Cabbagetown, parts of Riverdale, South Rosedale, and designated sections of Forest Hill are Heritage Conservation Districts. Any addition visible from the street triggers a Heritage Permit Application on top of the building permit and the (likely) Committee of Adjustment hearing. Rear additions in HCDs are generally feasible because they are not visible from the street; second-storey additions visible from the front face significant heritage scrutiny.
Add $5,000 to $15,000 in additional design and consulting fees for a heritage-sensitive project, plus six to twelve weeks of additional review time. Material choices get reviewed (no vinyl, often no aluminum, often a specified brick palette), window proportions get reviewed, and rooflines get reviewed.
When not to add
An addition is not always the right answer. Three cases where it usually is not:
You are doing it for resale within five years. The cost-to-value ratio on additions in Toronto is typically 0.6 to 0.8 — you spend $400,000 and add $260,000 to $320,000 to the home's market value. If you are not staying long enough to enjoy the space, the math is poor.
Your basement is unfinished. A finished basement adds 600 to 1,200 sq ft of usable space at $80 to $150 per sq ft. An addition adds 300 to 800 sq ft at $450 to $750 per sq ft. If you have not yet finished the basement, finish it first and re-evaluate. Our basement finishing piece walks through that math.
You are at FSI maximum and the design requires a Committee hearing for marginal benefit. If the variance you need is for an extra 80 sq ft and the hearing will cost $8,000 in design changes plus six months, the 80 sq ft is the most expensive square footage you will ever buy.
The case where an addition almost always pencils out: you love the lot, the location, the school, and the bones of the house, and you need 30 to 50 percent more usable space to fit the way your family lives. In that case the alternative is buying a different house at $400,000 to $700,000 of land transfer tax, mortgage costs, and moving disruption. The addition is the cheaper option, by a lot.
What permits cover
A typical Toronto rear addition needs:
- Building permit. Roughly $20 to $25 per sq m of new floor area in 2026, plus a fixed application fee. A 400 sq ft (37 sq m) addition runs $750 to $1,200 in permit fees.
- Plumbing permit. $250 to $600 depending on fixture count.
- Electrical permit (ESA). $200 to $500 depending on circuit count.
- Heritage Permit Application if applicable. $400 to $1,200.
- Committee of Adjustment application if applicable. $1,500 to $3,500 plus the hearing fee.
Permit fees are a small line item on a $300,000 addition. The schedule impact of getting them — that is the line item.
For more on permit math, see our permit cost piece.
What to do next
Get a designer or architect into the house before you talk to a contractor. The design dictates the cost, the variance risk, and the timeline. A good preliminary design with zoning analysis costs $3,500 to $8,000 and tells you in the first month whether you are looking at a 12-month project or an 18-month project. Use our cost calculator once you have a rough footprint to plan around.
