What a Garden Suite Actually Costs to Build in Toronto

A prefab garden suite vendor will quote $200,000 to $275,000 for a turnkey one-storey unit, and that number is real, but it's incomplete. It typically excludes site prep, permits, and the cost of running water, sewer, and hydro from the existing house to the new building. Three things a headline figure never captures actually set the final price: whether the build is one storey (60 square metres [646 ft²]) or the full two-storey maximum of 120 square metres (1,292 ft²), how far the new unit sits from the house's existing utility connections, and how the project gets financed against a home that's already carrying a mortgage and an insurance policy.

How big can you build, and why does that number drive cost?

Toronto caps a garden suite's gross floor area at 60 square metres (646 ft²) for a one-storey building, or 120 square metres (1,292 ft²) for a two-storey building, the maximum height the by-law allows. That cap comes from Zoning By-law 569-2013 Chapter 150.7, as amended by By-law 849-2025, which City Council passed on July 24, 2025. A two-storey suite is permitted, but only where the design clears the height, setback, and separation-distance rules already in the by-law: a site-specific test, not a given. For the full mechanics of what a given lot qualifies for, see Toronto Garden Suite Rules Explained for Owners and Builders.

Size is the first cost lever because every vendor quote is built around it. A 46 square metre (495 ft²) one-storey unit and a 115 square metre (1,238 ft²) two-storey unit aren't the same project priced twice. The foundation changes, the structural load changes, and the finishing list gets longer, and the quote moves with all three.

The cost drivers a prefab price doesn't show you

Toronto's own guidance is explicit that water supply and sanitary pipes for a garden suite are meant to connect from the primary dwelling on the lot, not a new municipal tap. That single detail is why servicing distance matters more than almost any other line item. A suite built ten metres (32'-10") from the back of the house needs a short, cheap trench; a suite pushed to the rear of a deep lot needs that same trench run three or four times as far, through a yard that may also need regrading. A prefab vendor's turnkey number rarely prices that trench in, because it depends on the lot, not the building.

Tree protection is the second driver most buyers don't see coming. Toronto won't approve a garden suite design that requires removing a healthy protected tree, defined as one with a trunk 30 centimetres (12") or more in diameter on private property, and every application must include a Tree Declaration Form. If the footprint a buyer wants collides with a protected tree's root zone, the fix is redesign, not a fee: a smaller footprint, a different foundation, or a repositioned unit, and any of those change the price.

Foundation type is the third lever, and it tracks the other two. A shallow slab suits a light, single-storey unit close to grade. A full basement or a frost-protected footing for a two-storey suite adds excavation, formwork, and inspection time that a one-line prefab price rarely itemizes separately.

None of this is optional at the permit stage. A building permit is required before construction starts, and the design has to comply with the applicable zoning provisions, the Ontario Building Code, and the City's tree regulations before that permit is issued.

Prefab vs custom stick-built: what the quotes actually look like

Vendor-quoted ranges vary more by size and structure than by builder type. These are approximate, market-reported figures, not City or CMHC data, and none of them include the servicing and permit costs covered below.

On top of the build price, budget for design, permit filing, and utility connection work separately. That soft-cost line commonly runs $20,000 to $40,000, again an approximate market range rather than a City-set figure, and it's the piece a prefab headline price is least likely to include.

What Toronto adds on top of construction

City fees are small relative to construction cost but they're not zero, and they stack. At 2026 Toronto Building rates:

For a typical 56 square metre (603 ft²) garden suite, that works out to roughly $1,700 to $1,750 in City fees before any development charge: the $18.56 per square metre ($1.72 per sq ft) construction charge on 56 m² (603 ft²), plus the $56.33 unit fee, plus the $644.38 certificate.

A garden suite usually pays no City development charge: provincial law exempts one unit in a building ancillary to a house that has no more than two units, and the City exemption described below covers units two to six. For a suite neither exemption reaches, the City's Laneway and Garden Suite Development Charges Deferral Program defers the charge, calculated at the single-detached rate plus indexing, for 20 years from the date the building permit issues. It becomes payable if a new lot is created through a plan of subdivision, plan of condominium, or consent to sever within that 20-year window, unless the owner and any purchaser sign an Assumption Agreement before the property transfers. Separately, Toronto Municipal Code Chapter 415 exempts the second through sixth residential unit built on a single parcel, including a unit ancillary to the primary dwelling, from development charges entirely. The by-law that set this, By-law 845-2025, passed on July 24, 2025 and carries no end date. Which rule applies to a specific suite is the City's call at permit, so confirm it before you budget rather than relying on a vendor's marketing claim.

Financing it without disturbing the existing mortgage

Most garden suites get built against equity in the primary residence, and the two common routes carry different limits.

A home equity line of credit is capped, under OSFI's Guideline B-20, at 65% loan-to-value on its own. Combined with an existing mortgage in a single readvanceable structure, the total authorized limit can't exceed 80% loan-to-value, and anything drawn above the 65% threshold has to amortize rather than stay revolving.

CMHC offers an insured mortgage refinance specifically for building a secondary suite, which includes a garden suite. It allows up to 90% loan-to-value on an owner-occupied property of up to four units, capped at a maximum as-improved property value of $2,000,000, with a 30-year maximum amortization. Equity take-out isn't permitted under this option; the funds have to go toward constructing the suite, the suite can't be rented for less than 90 consecutive days at a time, and at least one unit on the property has to be occupied by the borrower or a related person rent-free.

Insurance is the step that gets skipped. Insurance Bureau of Canada guidance says to tell the insurer before renting out a secondary suite. A standard policy typically covers the unit itself but excludes a tenant's personal property, and undisclosed rental use can put coverage at risk if a claim is filed.

The payback math: rent against what was actually financed

The number that matters isn't the sticker price against monthly rent; it's the total amount financed against the rent collected over years. CMHC's 2025 data puts the Greater Toronto Area's purpose-built rental vacancy rate at 3.0%, with average two-bedroom rent at $2,034, up 3.5% year-over-year.

Take an approximate, illustrative case: a homeowner finances roughly $300,000 in construction, servicing, and permit costs for a mid-size suite. Renting it at that GTA average of $2,034 a month, about $24,400 a year before vacancy and operating costs, means the rent needs to run for roughly 12 years just to offset the amount financed, before interest, vacancy, or maintenance are counted. That horizon moves a lot depending on how much of the $300,000 sits on a lower-cost HELOC draw versus a fresh construction loan at a higher rate, which is exactly why the financing structure belongs in the decision, not just the build price.

How TESA prices and sequences a garden suite build

TESA prices garden suites against the same drivers this article walks through: unit size against the 60 m² (646 ft²) and 120 m² (1,292 ft²) caps, distance from the existing house to water, sewer, and hydro, and foundation type. TESA runs the zoning and servicing checks before pricing, so the quote reflects the lot rather than a marketing average, and TESA sequences the building permit, tree protection sign-off, and financing so the suite is ready for trades in one pass instead of stalling on a step that should have started earlier.