Garden Suite & ADU Cost in Ontario (2026 Guide)
If you are considering building a garden suite, converting your basement into a legal apartment, or adding any type of accessory dwelling unit to your property in Ontario, understanding the real costs involved is the first step to making a smart decision. ADU pricing varies significantly depending on the type of unit, the size, your municipality’s requirements, and how you plan to use the space.
This guide breaks down the actual cost of building a garden suite or ADU in Ontario for 2026, covers every major cost factor, and explains why pricing varies so much across the Greater Toronto Area. Whether you are in Toronto, Markham, Vaughan, or anywhere in the GTA, here is what to budget for.
How Much Does a Garden Suite Cost in Ontario?
A detached garden suite in Ontario typically costs between $200,000 and $400,000 depending on size, finishes, site conditions, and your municipality’s specific requirements. At the per-square-foot level, most garden suites in the GTA come in between $250 and $350 per square foot for standard construction.
Small Garden Suite (400–500 sq ft): $200,000 to $275,000
A compact one-bedroom unit with a kitchen, bathroom, and living area. This is the most affordable option for homeowners looking to add rental income or house a family member. At this size, you get a functional self-contained unit without the premium cost of a larger build.
Mid-Size Garden Suite (500–650 sq ft): $275,000 to $350,000
This is the sweet spot for most Ontario homeowners. A mid-size suite comfortably fits a one-bedroom or large studio layout with a full kitchen, four-piece bathroom, and enough living space to feel like a real home. Most garden suites built in Markham, Toronto, and Vaughan fall in this range.
Large Garden Suite (700–1,100 sq ft): $350,000 to $450,000+
A larger unit that can accommodate two bedrooms, a full kitchen, and separate living and dining areas. Two-storey garden suites with higher-end finishes or custom architectural designs sit at the top of this range. Premium projects with basements or custom features can exceed $500,000.
ADU Cost by Type
Garden suites are the most common type of ADU in Ontario, but they are not the only option. Here is how costs compare across the main ADU types:
Detached Garden Suite
Cost: $200,000–$450,000+
Per sq ft: $250–$350
Timeline: 6–12 months from design to occupancy
This is a standalone unit built in your backyard. It requires its own foundation, utility connections, and full construction. It is the most expensive ADU type but also offers the most independence and highest rental income potential. If you’re weighing a garden suite against expanding your main home, our guide to home addition services covers that side of the equation.
Basement Apartment Conversion
Cost: $60,000–$120,000
Per sq ft: $90–$140
Timeline: 3–5 months
Converting your existing basement into a legal secondary suite is the most affordable way to add an ADU. The space already exists, so you are primarily paying for finishing, a separate entrance, plumbing, electrical upgrades, and fire separation to meet code. If your ceiling height is too low, underpinning adds $30,000 to $50,000+. For a deeper look at basement project pricing, read our basement renovation cost guide or explore our basement renovation services.
Garage Conversion
Cost: $80,000–$150,000
Per sq ft: $150–$250
Timeline: 3–5 months
Repurposing an existing attached or detached garage into a living unit. Costs depend on whether the structure needs foundation work, insulation, and utility connections. This preserves your backyard space while creating a functional unit.
Laneway House
Cost: $350,000–$550,000+
Per sq ft: $300–$400+
Timeline: 8–14 months
A custom-built unit accessed from a rear laneway, most common in urban Toronto neighbourhoods. Laneway houses are premium projects that often involve complex site access, custom architectural design, and higher permit costs.
What Drives Garden Suite and ADU Costs
The final price of an ADU project in Ontario depends on several specific factors. Understanding these helps you plan realistically and avoid budget surprises.
Size and Layout
This is the single biggest cost driver. Every additional square foot adds $250 to $350 in construction cost for a garden suite. A two-bedroom layout costs more than a studio not just because of size but because of additional plumbing, walls, doors, and finishes.
Foundation Type
Garden suites can be built on full poured foundations, helical piles, or slab-on-grade. A full foundation costs more but adds longevity and the option for below-grade storage. Piles are faster and cheaper to install but limit your design options. Foundation costs alone can range from $15,000 to $50,000.
Site Conditions
Every backyard is different. Costs increase if you need tree removal, significant grading, retaining walls, or if utility connections (water, sewer, hydro, gas) require long runs from the main house. Difficult access for construction equipment also adds labour time.
Utility Connections
Connecting water, sewer, electrical, and gas to the garden suite is a significant cost. Short runs from the main house might cost $10,000 to $20,000. Longer distances, municipal connection fees, or the need for a separate hydro meter can push this to $30,000+.
Municipal Requirements
Permit fees, site plan approval costs, and required professional drawings vary by municipality. In Toronto, permit fees and drawings might total $8,000 to $15,000. In Markham, site plan approval for larger suites adds 6 to 8 weeks and additional fees. Vaughan requires a parking space for the garden suite in addition to the main dwelling.
Finishes and Fixtures
Standard builder-grade finishes keep costs at the lower end. Upgraded flooring, custom cabinetry, premium appliances, and high-end bathroom fixtures can add $30,000 to $60,000+ to the project. Most homeowners building for rental income opt for durable, mid-range finishes that look good and hold up to tenant use.
Design and Architecture
Architectural design fees range from $10,000 to $20,000 depending on complexity. Custom designs cost more than adapting pre-approved plans, which some municipalities like Toronto now offer to streamline the process and reduce design costs.
Is Building a Garden Suite Worth It?
From a financial standpoint, garden suites are one of the strongest investments an Ontario homeowner can make right now. Here is the math:
A mid-size garden suite in the GTA rents for $1,500 to $2,500 per month depending on location, size, and finishes. That is $18,000 to $30,000 per year in rental income. On a $300,000 build, you are looking at a 6 to 10 percent annual return on investment before factoring in property value appreciation.
Properties with legal ADUs also command premium valuations, often 15 to 25 percent higher than comparable homes without secondary units. So you are building equity while generating income. For context on how other renovation types affect home value, see our bathroom renovation cost guide — bathrooms are another high-ROI project for GTA homeowners.
Beyond the financial return, a garden suite gives you flexibility. Use it for aging parents now, rent it out later. House an adult child while they save for their own home. Convert it to a home office or studio. The use case can change as your life changes, but the value remains.
The Canada Secondary Suite Loan Program also provides up to $80,000 in financing for qualifying homeowners creating a new secondary suite, which can offset a meaningful portion of your upfront costs.
Garden Suite Costs in Toronto, Markham, and the GTA
Garden suite construction costs are broadly consistent across the Greater Toronto Area, but municipal requirements create some variation. Toronto’s pre-approved garden suite designs can save on architectural fees. Markham’s site plan process adds time but allows larger units up to 100 square metres. Vaughan’s parking requirements add modest cost for driveway or pad construction.
At The Renovators of Canada, we build garden suites and ADUs across Toronto, Markham, Vaughan, Richmond Hill, Scarborough, Mississauga, and the wider GTA. We handle design, permits, construction, and inspections as a turnkey service so you are not coordinating multiple contractors and consultants.
To understand the full scope and cost for your specific property, explore our ADU and garden suite construction services or see how our renovation process works from start to finish.
Ready to explore your options? Request a free consultation and we will assess your property and walk through the numbers together.
Garden Suite & ADU Cost FAQ
How much does it cost to build a garden suite in Ontario?
A detached garden suite in Ontario typically costs $200,000 to $400,000 depending on size, finishes, and site conditions. A small 400 to 500 square foot unit starts around $200,000, while a larger 700+ square foot suite with premium finishes can exceed $400,000. Per-square-foot pricing runs $250 to $350 in the GTA.
Is a basement apartment cheaper than a garden suite?
Yes, significantly. A basement apartment conversion typically costs $60,000 to $120,000 since the structure already exists. You are primarily paying for finishing, a separate entrance, fire separation, and code compliance. If underpinning is needed for ceiling height, add $30,000 to $50,000.
How long does it take to build a garden suite in Ontario?
Most garden suites take 6 to 12 months from design to occupancy. That includes 2 to 4 months for design and permits, then 4 to 6 months of construction. Basement apartment conversions are faster at 3 to 5 months total. Timelines vary by municipality — Toronto and Markham have different permit processing speeds.
Can I get financing to build a garden suite?
Yes. you can get pre-approved for up $100,000 through Financeit, one of our approved partners. The Canada Secondary Suite Loan Program provides up to $80,000 for qualifying homeowners building a new secondary suite. Traditional home equity lines of credit and refinancing are also common options. Some homeowners also use the projected rental income to qualify for additional financing.
How much rent can I charge for a garden suite in the GTA?
Garden suites in the Greater Toronto Area typically rent for $1,500 to $2,500 per month depending on size, finishes, and location. A well-finished mid-size suite in Markham or Toronto can command $2,000+ per month. That is $24,000 or more per year in rental income.
Do I need a permit to build a garden suite in Markham?
Yes. A building permit is required for all garden suites in Markham. Under Ontario’s Bill 23, garden suites are permitted as-of-right on most residential lots, meaning no zoning amendment is needed. However, Markham requires site plan approval for suites over 75 square metres, which adds 6 to 8 weeks to the process. T-ROC handles all permitting.