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Detached ADU
Detached ADU designed, permitted and built across the 30 municipalities of the Greater Toronto Area - zoning review, permit drawings and construction handled by one team.
Detached ADU - Overview
Key Takeaways
- Key features: Maximum permitted footprint calculation, Slab, crawlspace or full-basement options, Fully separate services and metering
Free-standing backyard dwellings that are neither laneway nor garden-suite specific - a detached unit sized to whatever the lot and by-law allow.
Features & Specifications
- Maximum permitted footprint calculation
- Slab, crawlspace or full-basement options
- Fully separate services and metering
- Accessible single-storey layouts
- Year-round insulated construction
Key takeaways
- A detached ADU stands as its own building on the lot - not a basement, not an addition, not a converted garage. In the GTA it takes two named forms: a laneway house on a lane-backed lot and a garden suite without one.
- Detached is the form owners choose when separation is the point - a tenant with their own building rents higher, and a parent with their own front door has actual independence.
- It is also the most expensive form, because nothing exists yet: foundation, envelope, roof and every service connection are new.
- Typical units are 500-600 sq ft on one storey at $200,000-$350,000 in the GTHA; a common worked example is 500 sq ft at $400/sq ft - about $200,000 for construction alone.
A detached ADU is a second dwelling that stands as its own building on the lot, physically separate from the house - not a basement, not an addition and not a converted garage. In the GTA it takes two named forms: a laneway house on a lot backing onto a public lane, and a garden suite on a lot without one. The construction is the same; the access, servicing and approval path differ.
Detached is the form owners choose when separation is the point. A tenant with their own building rents at a higher rate than a tenant sharing a foundation. A parent with their own front door and their own roof has actual independence. And a detached unit can be designed, sited and oriented on its own terms rather than around whatever the existing house allows. The tradeoff is cost: a detached build is the most expensive ADU form because nothing exists yet - foundation, envelope, roof and every service connection are new.
What this includes
- Free-standing second building - its own foundation, envelope, roof and service connections, not an addition
- Foundation engineered from soils and water table: frost-protected shallow slab, helical piles or full basement
- 500-600 sq ft single-storey and up to ~900 sq ft two-storey layouts where height limits permit
- Rear-yard access assessed for excavator and crane reach before the budget is set
- Independent hydro, water and drainage connections so the unit rents as a separate address
- Both detached forms handled - laneway house on lane lots, garden suite where there is no lane
- Permitted as-of-right under Bill 23 and O. Reg. 299/19, with no parking space required in Toronto
- Quoted in the GTHA band of $200K-$350K for 500-600 sq ft, or $300-$600/sq ft by site access and finish
Typical units are 500 to 600 sq ft on one storey, or up to roughly 900 sq ft over two where height limits permit. In the Greater Toronto and Hamilton Area a unit that size runs $200,000 to $350,000 to build, per figures Resimate CEO Sarah Cipkar gave CBC News in July 2025, or $300 to $600 per square foot depending on site access and finish. A commonly used worked example is 500 sq ft at $400/sq ft - about $200,000 for construction alone, before permits, utility connections and design fees. Permit review takes four to eight weeks; construction four to eight months; the honest end-to-end figure including design is eight to fourteen months.
Foundation choice is the first real engineering decision, made from soils and water table: a frost-protected shallow slab, a helical pile array where excavation is difficult, or a full basement where head height and storage justify the cost. Rear-yard access decides the rest of the budget, because a unit that cannot be reached by an excavator or served by a crane is built by hand.
Legally it is an additional residential unit under O. Reg. 299/19 as amended November 2024, permitted as-of-right under Bill 23 on most serviced lots already holding a detached, semi-detached or townhouse dwelling. Construction is to the Ontario Building Code with SB-10/SB-12 energy compliance, and conservation authority approval is mandatory inside TRCA or Credit Valley regulated areas since 1 April 2024. Toronto imposes no parking requirement for these units.
Detached ADU - Permits and Approvals by Municipality
What approval typically costs, and what the lots look like, in the GTA municipalities we build in most.
| Municipality | Typical approval fees | Lot typology |
|---|---|---|
| Toronto | $8,000-$14,000 in permit, development and plan-review fees | Narrow downtown lots with rear public laneways - Toronto has over 300 km of them, more laneway frontage than any other Canadian city. |
| Brampton | $5,500-$10,000 including Brampton registration and Peel charges | Deep newer-subdivision lots, many with an existing unregistered basement apartment that must be brought to Ontario Building Code fire-separation standard. |
| Mississauga | $6,500-$11,000 in City of Mississauga and Region of Peel charges | Large 1970s-90s subdivision lots with attached garages; garage conversions and rear coach houses are both common outcomes. |
| York | $8,000-$14,000 under the City of Toronto fee schedule | Older narrow semi-detached lots on a laneway grid, with frequent shared-driveway conditions that must be resolved before permit. |
| Etobicoke | $8,000-$14,000 under the City of Toronto fee schedule | Split personality - laneway-served lakeshore grid in Mimico and New Toronto, versus large treed lots in The Kingsway where garden suites dominate. |
| Ajax | $7,000-$12,000 including Durham Region charges | Compact 1990s-2000s subdivision lots where the required 1.2 m side-yard construction access sets the maximum module width we can crane in. |
| King | $9,000-$16,500 including York Region and septic charges | Estate and agricultural parcels, many over an acre, on private well and septic with moraine core-area restrictions. |
| North York | $8,000-$14,000 under the City of Toronto fee schedule | Deep post-war bungalow lots, commonly 50 ft × 120 ft, with rear yards large enough for a detached garden suite plus the required 1.5 m separation. |
Fee bands are indicative, drawn from project experience - confirm current tariffs with the municipality before budgeting.
Related Unit Types
Frequently Asked Questions
Everything you need to know about our services.
Free-standing backyard dwellings that are neither laneway nor garden-suite specific - a detached unit sized to whatever the lot and by-law allow. Concretely that means: maximum permitted footprint calculation; slab, crawlspace or full-basement options; fully separate services and metering; accessible single-storey layouts. One contract covers design, permit and construction, so there is no handoff between a designer and a builder halfway through.
Related service: Accessory Dwelling Units
On a 700 sq ft reference unit our estimate band runs $268,000-$359,500 in Brock up to $281,500-$377,000 in East York - roughly $383 to $402 per square foot. The spread is not a markup: this work involves a new foundation, new servicing and a full building envelope, and the per-municipality difference comes from approval fees, frost depth and snow load. Final pricing follows a site visit.
Related service: Accessory Dwelling Units
Yes - a building permit is required in every GTA municipality. Bill 23 (More Homes Built Faster Act, 2022) and O. Reg. 299/19 permit up to three residential units as-of-right on most serviced lots, so a rezoning application is usually not needed.
Municipal approval costs range from $5,500-$10,000 including Brampton registration and Peel charges in Brampton to $9,000-$16,000 including Peel Region and septic permit charges in Caledon, quoted separately from construction. Plan review typically takes four to eight weeks.
Related service: ADU Building Permit
All 30 municipalities of the Greater Toronto Area, from Toronto out to Clarington. Each one has its own by-law, fee schedule and review stream, and we file into the local one - the municipal page for your address carries that city's approval band, frost depth and building season.
Related service: Accessory Dwelling Units
Eight to fourteen months is the honest end-to-end range: design and drawings, four to eight weeks of plan review, then construction. Because this work is a new foundation, new servicing and a full building envelope, the build phase is the part that moves most between projects. Excavation is scheduled inside the local building season, and interior work carries on through winter.
Related service: Accessory Dwelling Units
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Ready to start your detached adu project? Send us your address and we will tell you what your lot allows, what it costs and how long the permits take.