The 2026 ranges
- Typical additions: $350 to $500/sq ft (Ontario average; Toronto often exceeds $650)
- Basic: from about $350; complex or high-end: $600 to $800/sq ft
- Second-storey additions: $375 to $550/sq ft; typical 800 to 1,200 sq ft projects run $300,000 to $550,000+ turnkey
- Soft costs: 15 to 25% of budget for design, structural engineering ($1,200 to $4,000 for studies) and permits, before the shovel
Brantford and Brant County projects generally land below the GTA end of each range. Worked example: a 400 sq ft rear family-room addition at the Ontario average pencils at $140,000 to $200,000 plus soft costs and HST.
Why additions cost more per foot than houses
An addition is all of a house's expensive parts (foundation, structure, envelope, roof tie-in) with none of its cheap repetition, plus surgery on the existing building: matching floor heights, marrying rooflines, flashing the junction. That junction is where budgets and bad additions both fail, which is why the engineering matters more than the renderings, as we explain on the additions service page.
"The addition conversations that go well start with the lot, not the room. Setbacks, grading and where the structure can actually land decide half the budget before design begins. I'd rather kill a bad addition idea in the driveway, free, than bill you through discovering it on paper."
Mitch Fraser, owner, Ontario Contracting Co.
Addition vs. moving: the honest math
Add the addition's cost to your current home's value and compare against buying the bigger house, minus land-transfer tax, realtor fees, moving costs and the mortgage-rate reset. When the lot, neighbourhood or school catchment is the thing you can't replace, the addition usually wins; when your house needs the addition AND a full renovation, buying sometimes does. In-law suite additions carry one extra credit: eligible multigenerational units can claim the federal MHRTC, up to $7,500, detailed in the tax-credit guide. Wider per-square-foot context sits in the per-square-foot reference table.