Accessory Dwelling Units (ADUs) in Toronto & the GTA
Basement suites, garden suites, laneway houses and in-law units, designed, permitted and built by one team. Legal basement ADUs from $80 per square foot, backyard suites in Toronto from $199,999.
What an ADU is, and what Ontario calls it
An accessory dwelling unit, or ADU, is a second, self-contained home on a property that already has a house: its own kitchen, bathroom, sleeping area and entrance. It can be a basement apartment, a unit carved out of the main house, a suite above a garage, or a separate building in the back yard.
Ontario's law uses a different name. The Planning Act and Ontario Regulation 299/19 call them additional residential units, and each GTA city has its own terms: Toronto says secondary suite, garden suite and laneway suite; Markham says coach house and garden home; Mississauga and Brampton say additional residential unit. Ajax and Vaughan are the two that use "ADU" officially. They all describe the same thing.
Since November 28, 2022, every serviced urban lot in Ontario can have up to three units as of right: three inside the house, or two in the house and one in a backyard building. We help you work out which kind of ADU your property can hold, then design, permit and build it, with one contract and one itemized price.
The ADUs we build
Most GTA properties have at least one realistic option. The right one depends on your ceiling height, your lot, whether there is a lane, and who the unit is for.
Basement ADUs
The most common ADU in the GTA. A legal basement apartment built to the 2024 Ontario Building Code, with the separation, alarms, windows and exits a second unit needs. We build them across the GTA.
Garden suites
A detached backyard home on a lot without a public lane, up to 60 m² on one storey or 120 m² on two in Toronto. We design and build garden suites across Toronto.
Laneway houses
A detached home at the back of a Toronto lot with at least 3.5 m of frontage on a public lane, up to 10 m long and 8 m wide.
In-law suites
A private suite for a parent or adult child inside the house, often on the main floor with an accessible bathroom. It can be built as a full second unit or as a family suite without a separate kitchen.
Addition-based ADUs
When the house has no room to spare, a rear or above-garage addition can create the space for a new unit, designed together with the rest of the house.
Legalizing an existing unit
Many GTA basement units were built without permits. We bring them up to the Building Code under a new permit, using the compliance alternatives available for houses at least five years old.
What Ontario allows on your lot
These provincial rules apply on every serviced urban residential lot in Ontario. Each city then adds its own zoning details on top.
Up to three units as of right
A city cannot prohibit two units in a detached house, semi or townhouse plus one in a backyard building, or three units inside the house. Several GTA cities, including Toronto and Ajax, now allow four.
Parking capped at one space per ADU
A city cannot require more than one parking space for each additional unit, and the space can be tandem. Toronto and Mississauga require none at all.
No minimum unit size, no owner rule
Cities cannot set a minimum floor area for an ADU. Under Ontario Regulation 299/19 the owner does not have to live on the property, and the tenant does not have to be related.
More room for backyard units
Since November 2024, a building containing an ADU can exceed angular planes, is not limited by floor space index, and gets up to 45% lot coverage, subject to the city's height and setbacks.
No development charges
The second unit, a third unit in the house and one unit in a backyard building are exempt from development charges under the Development Charges Act.
The Building Code still applies
Every ADU needs a building permit and must meet the Ontario Building Code for fire separation, alarms, ceiling height, windows, exits and sound. Some cities also require registration.
Backyard ADUs are now permitted in Mississauga, Brampton, Vaughan, Markham, Richmond Hill, Oakville and Ajax as well as Toronto, each with its own size, height and setback limits. Our guide What Is an ADU in Ontario? sets out the rules city by city.
Which ADU fits your property?
A quick way to see where to start. We confirm it on site before you spend anything on drawings.
| ADU type | Usually works when | Where we build | Our pricing |
|---|---|---|---|
| Basement ADU | The basement has, or can get, 1.95 m of clear height and room for bedroom windows and an exit | Across the GTA | From $80 per sq ft |
| Garden suite | A deep enough back yard, no public lane, and a workable fire-access path from the street | Toronto | Complete packages from $199,999 |
| Laneway house | At least 3.5 m of the lot runs along a public lane | Toronto | Complete packages from $199,999 |
| In-law or interior suite | A main floor, upper floor or attic with space to spare | Across the GTA | Quoted after a site visit |
| Addition-based ADU | The lot has room to build out or up, within the zoning | Across the GTA | In-law suite additions typically $80,000 to $200,000 |
What an ADU costs
A legal basement ADU is usually the least expensive way to add a unit, because the structure, foundation and services already exist. Ours start at $80 per square foot, and most legal basement apartments in the GTA cost $80,000 to $175,000. Lowering the floor, adding a below-grade entrance and enlarging windows are what push a project toward the top of that range.
A backyard suite is a small house, with its own foundation, roof and servicing. Our complete garden suite and laneway house packages start at $199,999 for a compact one-storey suite on a straightforward lot, and most Toronto backyard suites cost about $200,000 to $400,000.
Every project gets an itemized, fixed quote after we review the property. For a side-by-side breakdown, read How Much Does an ADU Cost in Toronto and the GTA?
Paying for an ADU in 2026
The financing options that actually exist today, and one tax point most owners miss.
CMHC's 90% refinance
An owner-occupier adding a legal suite can refinance with mortgage insurance up to 90% of the home's value after the work, on properties worth under $2 million with up to four units, amortized over up to 30 years. Rentals under 90 days are not allowed. Our suite financing guide walks through an example.
Multigenerational Home Renovation Tax Credit
If the ADU is for a family member who is 65 or older, or an adult eligible for the disability tax credit, the federal credit covers up to $50,000 of costs: 14.5% (up to $7,250) for 2025, and 14% (up to $7,000) from 2026.
The $80,000 suite loan does not exist
The federal Canada Secondary Suite Loan Program was cancelled in the 2025 federal budget before it launched. Content that still advertises it is out of date.
HST on rented backyard suites
Under CRA guidance, an owner who builds a detached suite and rents it to someone who is not a relative is generally treated as a builder and must self-assess HST on its fair market value, with a partial rebate that may be available. Speak to your accountant before you start.
How an ADU project works
One team from the first site visit to the final inspection.
1. Property assessment
We check zoning, ceiling height, windows, exits, servicing, fire access and parking, and tell you which ADU options your property can actually hold.
2. Design and drawings
Drawings by a qualified designer, architect or engineer, using the Building Code's compliance alternatives for older houses, or a city's pre-approved plans where they fit.
3. Permits and approvals
The building permit, any minor variance, conservation authority or tree permits, and the ESA notification for electrical work.
4. Construction
Built to the approved drawings, with every required inspection booked and passed in sequence.
5. Close-out and registration
Final inspection, permit closed, and registration or licensing where your city requires it, such as Brampton, Mississauga, Markham and Pickering.
6. Ready to live in or rent
A legal, insurable unit you can rent with confidence or hand over to family.
ADU questions
What is an ADU in Ontario?
An accessory dwelling unit is a self-contained second home on a property with an existing house, such as a basement apartment, garden suite, laneway house or in-law suite. Ontario's Planning Act calls them additional residential units.
How many ADUs can I build on my lot?
On a serviced urban lot, Ontario lets you have up to three units as of right: three inside the house, or two in the house and one in a backyard building. Some cities, including Toronto and Ajax, allow four.
How much does an ADU cost?
Our legal basement ADUs start at $80 per square foot, and most legal basement apartments in the GTA cost $80,000 to $175,000. Our garden suite and laneway house packages start at $199,999, and most Toronto backyard suites cost about $200,000 to $400,000.
Do I need a permit to build an ADU?
Yes. Every ADU needs a building permit and must meet the Ontario Building Code, and electrical work needs a separate ESA notification. Some cities also require the unit to be registered after the permit is closed.
Do I have to live on the property?
No. Ontario Regulation 299/19 says a city cannot require the owner to live on the property, and the person living in the ADU does not have to be related to the owner. CMHC's 90% refinance is a separate matter and is for owner-occupiers.
Do I need parking for an ADU?
A city can require at most one parking space for each additional unit, and it can be tandem. Toronto and Mississauga require no additional parking, and Ajax requires none for the first additional unit.
Are ADUs exempt from development charges?
Yes. Under the Development Charges Act, the second unit, a third unit in the house and one unit in a backyard building are exempt from development charges.
Can I build a backyard ADU outside Toronto?
Yes, in most GTA cities. Mississauga, Brampton, Vaughan, Markham, Richmond Hill, Oakville and Ajax all now permit a detached backyard unit, each with its own size, height and setback limits. We build backyard suites in Toronto and basement and in-house ADUs across the GTA.
Is there a government grant for building an ADU?
There is no province-wide ADU grant open in Ontario in 2026, and the federal $80,000 suite loan was cancelled. The main supports are CMHC's 90% refinance, the development charge exemption and, for family members who qualify, the Multigenerational Home Renovation Tax Credit.
How long does it take to build a basement ADU?
A legal basement suite typically takes 8 to 12 weeks on site, after about 2 to 3 months of design and permits. Lowering the floor or adding a new below-grade entrance takes longer.
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