Based on the permit sets and takeoffs we analyze, a typical GTA custom build breaks down roughly like this:
| Division | Share of construction cost | Notes |
|---|---|---|
| Excavation, shoring & foundations | 12–20% | The big variable — see below |
| Structure & framing | 15–18% | Engineered joists and LVLs are standard now |
| Envelope (roof, cladding, windows) | 15–20% | Windows alone often run $30,000–$60,000 |
| Mechanical, electrical, plumbing | 15–18% | |
| Interior finishes & millwork | 20–30% | Kitchens/millwork commonly $40,000–$80,000 custom |
| Site, general conditions, other | 8–12% | Fencing, protection, bins, supervision |
The lot, more than the house. A 25-foot infill lot with neighbours a few feet away can add $80,000–$150,000 before the house even starts: shoring the excavation, underpinning the neighbours' foundations (see our underpinning guide), tree protection hoarding, and trucking soil off a street where nothing can be stockpiled.
Basement depth. Every extra foot of depth adds excavation, disposal (soil swells 30–40% when dug — here's the math), taller foundation walls, and more formwork.
Flat roofs and parapets. Beautiful, common on modern infills, and more expensive per square foot than trussed roofs: TPO membrane, tapered insulation, metal copings, scuppers.
Land transfer tax (double in Toronto), demolition of the existing house ($25,000–$50,000), utility disconnects/reconnects, a geotechnical report, arborist reports and tree security deposits, site insurance, and HST. Soft costs typically add 15–25% on top of construction.
Rule of thumb we use: whatever the per-square-foot number says, an infill lot in the old city adds 15–25% versus the same house on an open suburban lot.
How much does it cost to build a house in Toronto per square foot?
In 2026, most GTA custom builds price between $350 and $550 per square foot for construction alone. High-end finishes or difficult infill lots can exceed $600/sq ft; simple builds on open lots can come in below $350.
Does that include the basement?
Per-square-foot figures are usually quoted on above-grade floor area, with a standard finished basement absorbed in the rate. A deep basement, walkout, or underpinned basement adds real cost on top.
What's the single biggest hidden cost?
On tight Toronto lots: shoring and underpinning — commonly $50,000–$100,000+ combined, and mostly invisible until the excavator shows up.
How accurate is a per-square-foot estimate?
Good for planning, weak for decisions. Real accuracy comes from a material takeoff of your actual drawings — quantities of concrete, framing, windows and finishes priced line by line. That's what our tool does.