Second Storey Addition: Cost, Structure and What's Involved

Adding a second storey means taking the roof off, building a new floor on the walls and foundation already there, and living somewhere else for 5 to 7 months while it happens. Toronto builders price it at about $350 to $650 a square foot. The first question comes before any price, though: whether the house can carry the new floor, since an older bungalow's foundation may need reinforcing or underpinning first.

What a second storey addition costs

The prices below are Ontario builders' published 2026 figures for Toronto and Kitchener-Waterloo. One Toronto builder prices the finished job, another prices construction before HST and soft costs, and the others do not say, so the table gives the basis where the builder states it.

On one Toronto builder's 2026 figures, a second storey runs $450 to $650 a square foot, against $450 to $550 for a rear addition and $550 to $800 for a third storey. A Kitchener-Waterloo builder puts a second storey at $250 to $400+ a square foot, against $350 to $650 for the same floor on home additions in Toronto.

Within those ranges, scope sets the number. A partial storey over a garage or one wing costs less than a full floor, and each bathroom adds plumbing to a level that had none: one Toronto builder puts the saving from one bathroom instead of two at $20,000 to $40,000. The new staircase has to land somewhere on the main floor, and work under the addition, such as raised ceilings or new wiring, is its own line in a builder's breakdown.

Can your house support a second storey?

The structural check comes before any design work: the foundation and footings, the main-floor walls, and the posts and beams in the basement all have to carry a floor they were never built for. The main-floor ceiling joists were sized for a ceiling and an attic, so the new floor usually gets joists of its own, and the new stairs need an opening cut through the main floor.

Older houses are where the answer gets expensive. A Toronto design-builder warns that 1940s to 1960s bungalows on clay brick foundations, several bricks thick, may need reinforcing or underpinning the foundation before any framing goes up.

In Toronto, a second storey that also strips and reframes the main floor can cross the zoning by-law's line of 50% of the main walls removed or replaced, after which the house has to meet today's zoning. When the foundation needs work on every wall and the zoning caps the height, the cost starts to approach tearing down and rebuilding, so price both before committing to either.

Permits and zoning for a second storey

Raising a house by a storey needs a building permit in Toronto, Vancouver, Calgary and Edmonton, and Toronto lists second-storey additions by name. Its small residential additions guide asks for a survey or site plan, floor plans showing the structural framing above, a roof plan, elevations with the overall building height, cross-sections, and footing and foundation details. An addition over 100 m² also needs the City's infill construction notice posted on the site.

Zoning is the slower gate. The new floor has to fit the limits on height, side yards, floor space and lot coverage, and Toronto's House Stream reviews a complete application for an existing detached or semi-detached house within 10 business days, but it counts as complete only once the zoning certificate (ZAP) is issued. A design that does not fit needs a minor variance from the Committee of Adjustment, which charges $2,228.98 in 2026 for an addition to a house of three units or less, and double for a variance sought after the work is built.

Under Ontario's Planning Act, the applicant, the Minister or a specified person or public body can appeal a variance decision within 20 days; neighbours are not on that list. Scaffolding, a bin or stored materials can also need a Toronto tree permit: any work that can injure a tree 30 cm or more in diameter, measured 1.4 m above the ground, needs one, as does work affecting a city street tree of any size.

Elsewhere, Vancouver's one-week fast track excludes additions to an existing building and any job over $250,000, so a second storey takes the regular permit path. Calgary requires at least a building permit for every addition, and its common rule for an upper-floor addition, no higher than the existing roof and under 10 m², is one a full second storey goes past.

Who draws the plans

In Ontario the drawings come from a designer qualified under the Building Code, an architect or an engineer. Toronto asks a qualified designer to put a name, registration number and qualification identification number (the BCIN) on the drawings, with a Schedule 1 form for every designer except engineers and architects; an owner exempt from the qualification rules states the reason on the same form. The structural drawings for a second storey normally carry an engineer's seal, and Calgary says an architect or professional engineer may be required, with stamped plans where they are.

Second storey addition timeline, from design to move-in

Toronto builders put a second storey at 12 to 18 months from the first design meeting to move-in, or 10 to 14 months from a signed contract. The permit is the swing: one builder quotes 3 to 5 months for a Toronto permit, and a variance adds 2 to 4 months more.

The build starts below, goes up through the roof, and once the new floor is closed in follows the order of a full-home renovation, with the framing and rough-ins inspected before anything is covered:

1. Move out and protect. Furniture goes into storage and the main floor is covered against dust and water.
2. Structure below. The posts, beams, footings or underpinning the engineer called for go in.
3. Roof off. The roof and attic come off, and a temporary cover keeps the weather out.
4. Framing. New floor joists, walls and roof are framed, and the stair opening is cut.
5. Closed in. Roofing, sheathing and windows make the house weathertight again.
6. Rough-ins and inspection. Plumbing, heating ducts and wiring extend upstairs, and the framing and rough-ins are inspected.
7. Insulation, drywall and finishes. Stairs, flooring, bathrooms and paint, plus repairs to the main floor below.
8. Final inspection and move back. The permit is closed and the family moves home.

Moving out during the build

With the roof off, the house is open to the weather and the stairs and main floor are a work site. A Toronto builder puts the time living elsewhere at 5 to 7 months, and at $4,000 to $10,000 a month in rent that adds $20,000 to $70,000 before storage.

What to settle before you sign