Every year we get about a dozen calls from bungalow owners in Oakville, Mississauga, or East Toronto who've outgrown their house, love the lot, and want to know what it would cost to add a second storey instead of moving. The answer is always a larger number than they expect, and it's the single biggest-ticket job we quote outside of full custom builds.
This post is the honest 2026 breakdown — where the money goes, what the realistic ranges look like, and the decisions that move the total by $40,000 in one conversation. For the structural beam decisions that get made inside the envelope, pair it with our LVL vs steel vs glulam beam comparison.
Framing the job: we're going to cost out the most common GTA second storey addition — adding a full second floor of roughly 1,100 to 1,400 square feet over an existing 1960s or 1970s bungalow. That means demolishing the existing roof, reinforcing or replacing the existing foundation if required, framing a new second floor on top of the ground-floor walls, building out bedrooms and a bathroom, and capping with a new roof.
The homeowner stays in the house during part of the project (usually not all of it). This is the standard GTA addition scope we sign three to five times per year through our framing and structural service.
The total range: $380,000 to $720,000 CAD in 2026
A full second storey addition on a GTA bungalow in 2026 runs $380,000 to $720,000 CAD for a typical 1,100 to 1,400 square foot addition, fully finished. That's a big range — call it $280 to $520 per square foot of new space — and the driver is almost entirely the finish tier and the foundation question.
A second storey built with builder-grade finishes, stock windows, laminate flooring, and a simple asphalt shingle roof lands at the bottom. A second storey with hardwood floors, custom casing, a higher-end en-suite bathroom, and a standing-seam metal roof lands at the top. Same envelope, roughly double the total. The roof material choice alone is worth reading our roof replacement cost breakdown before you sign.
Before any of the framing numbers matter, there's a foundation question. Does the existing foundation of the bungalow have enough capacity to carry a second storey? About 60% of the 1960s and 1970s bungalows we quote in the GTA can carry the load as-is, because the footings were overbuilt for a single-storey structure and the engineer can sign off after a site review.
The other 40% need foundation reinforcement — either underpinning, adding helical piles around the perimeter, or (in rare cases) partial replacement of the footing. If your existing foundation needs help, add $60,000 to $130,000 to everything below.
- Survey, site plan, soil report if required: $3,200 to $7,500
- Architectural design and drawings: $18,000 to $45,000 for a 1,100–1,400 SF addition
- Structural engineering and stamped drawings: $7,500 to $16,000
- Permits (building, plumbing, ESA, lot grading): $4,800 to $11,000
- Foundation review or reinforcement (if required): $0 to $130,000
Demo, temporary weather protection, and the first two weeks
The first two weeks of a second storey addition are the worst. We strip the existing roof off the bungalow, which means the house is effectively unroofed for that period. The logistics around keeping the weather out of the house while this is happening is non-trivial — it involves an engineered temporary weather enclosure, usually a frame of 2x4s clad in 6-mil poly or a rented shrink-wrap tent system, and it gets set up before the first shingle comes off. We quote this as a line item because it's real money and it's the thing homeowners don't expect.
Temporary weather protection on a typical 1,200 SF second storey addition runs $8,500 to $18,000 CAD. The low end is a poly-and-2x4 enclosure that we build and rebuild daily as framing progresses. The high end is a rented shrink-wrap tent from Rainier Tents or similar, which stays up for the entire framing phase and protects the whole existing ground floor.
On a job we did in Thornhill in 2024, the homeowner wanted to stay in the house during construction, so we specified the rented tent. Worth it, but a $17,000 line.
Demo itself is $6,800 to $14,000 for roof tear-off on a standard bungalow — removing the existing shingles, underlayment, rafters, and ceiling joists, hauling everything to a transfer station, and protecting the ground-floor interior. We don't touch the existing walls during this phase; the old top plates become the bearing points for the new second floor system. If the engineer finds rot or damage in the existing top plates, we'll flag it and add a remediation line — usually $3,000 to $8,000 depending on the span.
- Roof demo and haul-away: $6,800 to $14,000
- Temporary weather protection (poly enclosure): $8,500 to $12,000
- Temporary weather protection (rented shrink-wrap tent, recommended if staying in house): $12,000 to $18,000
- Top plate remediation if damage found: $3,000 to $8,000
- Protection of ground-floor interior during framing: $1,800 to $3,400
Framing the second floor and the new roof
Framing is the biggest labor line on a second storey addition. We're building a full floor system — typically 2x10 or engineered I-joist floor joists at 16" on centre over the existing top plates, sheathed in 3/4" T&G plywood, glued and screwed. Then all of the second-floor exterior walls (2x6 with OSB sheathing), all of the interior partitions, and a new truss or stick-framed roof over the top.
For a 1,200 square foot addition, framing labor and material runs $85,000 to $145,000 CAD.
Truss versus stick-framed roof is the question we get every time. Pre-engineered roof trusses from a truss plant (we work with Roseburg or Triforest in Ontario) are faster to install and cheaper in material — usually about $18,000 to $28,000 for a 1,200 SF addition.
Stick-framed (cut and built on site with rafters, ceiling joists, and ridge beams) is $24,000 to $38,000 for the same span but gives you cathedral ceilings, attic storage, and custom roof pitches that a truss won't deliver. We default to trusses for standard hip or gable roofs and stick-framing for any roof with a cathedral interior or unusual geometry.
Sheathing, housewrap, windows, doors, and roofing round out the framing and envelope phase. A second-storey addition typically uses 12 to 20 windows, mid-tier double-hung or casement from a brand like Marvin, Pella, or JELD-WEN, at $1,200 to $2,400 per window installed depending on size and glass. Add one or two exterior doors and a balcony door if the design calls for it.
Asphalt shingle roofing for a 1,200 SF second storey runs $11,000 to $17,000. Standing seam metal is closer to $26,000 to $42,000. Our asphalt vs metal vs cedar shake roofing comparison unpacks which one to pick on a long-hold house.
- Floor framing (joists, subfloor, glue/screw): $18,000 to $28,000
- Exterior wall framing (2x6 + OSB sheathing): $22,000 to $34,000
- Interior partition framing: $12,000 to $20,000
- Roof framing — trusses: $18,000 to $28,000 installed
- Roof framing — stick-framed: $24,000 to $38,000 installed
- Windows (12 to 20 units mid-tier): $14,400 to $48,000
- Exterior doors (1 to 3 units): $2,400 to $7,200
- Roofing — asphalt shingle: $11,000 to $17,000
- Roofing — standing seam metal: $26,000 to $42,000
- Housewrap, flashing, soffit and fascia: $4,200 to $7,800
Mechanical, electrical, plumbing — and why this line is always bigger than expected
The mechanical trades on a second storey addition are where the quotes from different contractors diverge the hardest, because it's not as visible as framing and homeowners don't have instincts for what it should cost. A full second-floor HVAC upgrade — new ductwork for every room, a new second-zone on the existing furnace or a dedicated heat-pump mini-split system, a new bathroom exhaust fan, radon vents if required — runs $18,000 to $42,000 CAD depending on whether the existing HVAC system can handle the new load or needs to be replaced.
Plumbing for a new second-floor bathroom plus any additional sinks runs $14,000 to $28,000 including all rough-in, supply lines, waste and vent, and final fixtures. The wider variation is whether the new second-floor bathroom is stacked over the existing ground-floor plumbing wall (cheaper) or located at the far end of the new floor (requires longer drain runs and more vent complexity). Ontario Building Code requires every plumbing fixture to be properly vented to the outside, and a long drain run on a second storey addition can require a vent stack through the new roof.
Electrical is $14,000 to $26,000 for a typical second storey addition — new circuits for every bedroom, bathroom, hallway, and closet, a dedicated 20-amp circuit in each bedroom per current ESA code, smoke and CO detectors on battery backup hardwired to the building, new panel if the existing panel is already at capacity (common on 100-amp services from the 1960s), and all rough-in and final fixtures.
We usually need to upgrade the service from 100-amp to 200-amp on a second storey addition, which adds $4,200 to $7,800 including the ESA permit and Toronto Hydro (or whichever utility) coordination.
- HVAC (new second-zone ductwork or mini-split): $18,000 to $42,000
- Plumbing rough-in, fixtures, final connections: $14,000 to $28,000
- Electrical rough-in, panel upgrade, fixtures, ESA permit: $14,000 to $26,000
- Service upgrade 100A to 200A if required: $4,200 to $7,800
- Insulation (R-22 walls, R-50 attic): $8,200 to $14,500
- Drywall, prime, paint: $22,000 to $38,000
Finishes, fixtures, and the final push
Interior finishes are where a second storey addition becomes a version of the kitchen renovation cost conversation. Flooring across 1,200 SF runs $14,400 to $38,400 depending on whether it's laminate ($12/SF installed) or engineered hardwood ($32/SF installed) or real hardwood matched to the existing ground floor ($34/SF installed plus a transition detail at the stairs).
Trim and interior doors run $18,000 to $38,000 including baseboard, casing, interior doors, closet doors, and the finish carpentry. A staircase between the ground floor and the new second floor runs $8,000 to $24,000 depending on whether it's a basic straight run with carpet or a built-to-order oak-and-steel feature stair.
The bathroom or bathrooms on the new floor follow the same pricing we laid out in the bathroom renovation cost breakdown — $24,000 to $45,000 for each standard bathroom. A primary en-suite at the higher end of that range. A second smaller main bathroom at the lower end. Two bathrooms on a new floor is common on 1,400 SF additions and is the scope that pushes the total toward the top of the cost range.
“We budgeted $400k. You told us on day one it would be $560k with the foundation work included. You were within eight grand of your quote at the end. That's the whole reason we trusted you.”
The reason we price second storey additions this way — with every line broken out, every trade visible, every decision documented — is that a $500,000 project deserves a $500,000 conversation. The gap between a $380,000 quote and a $720,000 quote on the same 1,200 SF addition is almost always visible on the line-item sheet: different roof, different windows, different bathroom fixtures, different flooring.
A homeowner who sees the breakdown can trim $40,000 off the total in one afternoon of decisions. A homeowner who sees only a single number has to either accept it or walk away. Our job is to put the sheet in front of them and let them choose.
