ADU & Garden Suite Construction in Ontario
Ontario’s housing crisis is driving unprecedented demand for accessory dwelling units (ADUs) and garden suites. Whether you’re looking to build a detached garden suite in your backyard, convert your basement into a legal secondary apartment, or renovate a garage for additional living space, T-ROC has the expertise to guide you from design through permit approval to turnkey construction.
Since Ontario’s More Homes Built Faster Act (Bill 23) passed in 2022, garden suites and secondary units are now permitted across most of the province as-of-right, meaning no costly zoning amendments are required. However, building permits, code compliance, and municipal regulations still require expert navigation — and that’s where T-ROC excels.
We’ve helped dozens of GTA homeowners unlock the potential of their properties by building ADUs that generate rental income, accommodate aging parents, increase property values, and provide housing flexibility. Let’s explore your options.
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Types of ADU’s We Build
Garden Suites (Detached Backyard Units)
A garden suite is a small, self-contained dwelling unit located in the backyard of a residential property. Typically 500–1,100 square feet, garden suites can be one or two storeys and include all essential amenities: bedroom, kitchen, bathroom, and living area. Under Ontario's current zoning rules, garden suites are legally permitted on most residential lots.
Best for: Multi-generational families, rental income, guest accommodations, or maximizing underutilized backyard space
Basement Apartments & Secondary Suites
Converting your basement into a legal secondary suite is often the most affordable ADU option. A basement apartment includes a separate entrance, egress (emergency exit window), kitchen, bathroom, and living/sleeping areas — all to Ontario Building Code standards.
Best for: Budget-conscious homeowners, existing homes with established basements, or quick ROI.
Garage Conversions
Transform an existing garage or carport into a functional living unit. While slightly more constrained than new construction, garage conversions preserve your backyard space and use existing structures efficiently.
Best for: Properties with unused garage space, minimal lot disruption, creative multi-use designs.
Laneway Houses & Side Yard Units
Where applicable in municipalities like Toronto and portions of the GTA, laneway houses provide access from rear laneways. These are increasingly popular in urban neighbourhoods and offer unique design opportunities.
Best for: Urban properties with rear lane access, maximum density on constrained lots.
Pro Tip: Most homeowners recover their ADU investment in 3–5 years through rental income alone. At $1,500–$2,500/month rental rates (standard for GTA ADUs), you’re generating $18,000–$30,000 annually while building permanent property value.
ADU & Garden Suite Costs in Ontario (2026)
ADU costs vary significantly based on type, size, finishes, and whether existing structures are repurposed. Here’s what homeowners in Ontario typically invest:
Garden Suite Construction
- Range: $180,000–$350,000+ for a standard 600–1,100 sq ft detached garden suite
- Cost per sq ft: $250–$350/sq ft depending on finishes and site conditions
- Premium projects: Custom 2-storey suites with high-end finishes can reach $400,000–$600,000+
- Timeline: 6–10 months from permit approval to occupancy
Basement Apartment Conversion
- Standard conversion: $63,000–$120,000 for a 700 sq ft basement suite
- Cost per sq ft: $90–$140/sq ft for code-compliant secondary suites in the GTA
- With underpinning: Add $30,000–$50,000+ if ceiling height requires excavation
- Professional fees & permits: $2,500–$8,000 (drawings, permits, inspections, site plan)
- Timeline: 3–5 months for straightforward conversions
What Affects ADU Costs
- Site conditions (soil type, tree removal, grading, servicing)
- Municipal requirements and site plan complexity
- Utilities (hydro, gas, water, sewer connection distances)
- Finishes and appliance selections
- Permit timelines (varies by municipality; can delay projects 2–8 weeks)
ADU Regulations in Ontario (2026)
Ontario’s regulatory landscape for ADUs has shifted dramatically over the past three years. Here’s what you need to know:
Provincial Framework: More Homes Built Faster Act
Under Bill 23, Ontario now permits up to three residential units per residential lot as-of-right, meaning:
- No zoning amendment required (saves time and money)
- Garden suites are legally permitted on most residential properties
- Secondary suites in the principal residence are permitted
- Second and third units are exempt from Development Charges and Site Plan Control in most cases
- Municipal water and sewer services must be available
Municipal Regulations: Key GTA Cities
Markham
- Garden suites permitted on detached residential lots (min. 15m frontage, 465 sq m area)
- Max. 100 sq m (1,076 sq ft) with 6.5m height limit (accommodates 2-storey units)
- Site plan approval required for suites over 75 sq m (adds 6–8 weeks)
- T-ROC navigates Markham’s permitting process — we know the checklist
Toronto
- Garden suites permitted in R, RD, RS, RT, and RM residential zones
- Footprint limited to 40% of rear yard or 60 sq m (646 sq ft), whichever is smaller
- Combined ancillary structure coverage cannot exceed 20% of lot area
- No parking required; 2 bicycle parking spaces minimum
- Emergency fire access: 1.0m minimum width, 45m max distance from public street
- Toronto offers pre-approved garden suite designs that streamline permits
Vaughan
- Garden suites permitted in R1, R2, R3, R4 zones (min. 15m frontage, 450 sq m area)
- Max. 80 sq m (861 sq ft) with 6m height restriction
- Unique requirement: 1 parking space required for the garden suite in addition to principal dwelling parking
Permits & Building Code
Regardless of zoning, all ADUs require:
- Building permit from your municipality
- Compliance with Ontario Building Code (electrical, plumbing, structural, egress, ventilation)
- HST clearance certificate
- Inspection at rough-in and final completion stages
- Occupancy permit
T-ROC handles all permitting. We prepare architectural drawings, manage municipal correspondence, and shepherd your project through inspections — so you don’t have to navigate the bureaucracy alone.
Why Build an ADU or Garden Suite?
Rental Income & Cash Flow
Garden suites and basement apartments in the GTA typically rent for $1,500–$2,500/month. That’s $18,000–$30,000 annually in passive income, helping you offset mortgage costs and building long-term wealth.
Multi-Generational
House aging parents, adult children, or extended family members on your property while maintaining privacy and independence. It’s more affordable than assisted living and keeps families connected.
Increased Property Value
Properties with legal ADUs command premium valuations — often 15–25% higher than comparable homes without secondary units. You’re not just generating rental income; you’re building equity.
Housing Flexibility
Life changes. An ADU gives you flexibility: rent it out during peak earning years, use it for guests or hobby space later, or create a mortgage helper while you’re paying down debt.
Solving Ontario’s Housing Crisis
By building an ADU, you’re part of the solution to Ontario’s severe housing shortage. Garden suites increase housing density without sprawl, preserving green space while meeting growing demand.
Homeowners Across the GTA Love Their New Spaces
Jason Murray
TROC came recommended to me from a trusted source. I can see why he uses them. Professional, clear communication, quality results in a reasonable time frame. If you’re tired of chasing after solo operators, use TROC. They are run like a professional business
Dan C.
Renos are always stressful; but we honestly can say that David, William and the T-ROC team have made this as easy and painless as it possible could have been.
Paul G., Whitby
Professional from start to finish. Their team guided us through every detail and delivered exactly on time.
Why Choose T-ROC for Your ADU Project?
Deep ADU Expertise
We've built dozens of garden suites, basement apartments, and garage conversions across the GTA. We understand each municipality's unique requirements, building inspectors' expectations, and common pitfalls.
End-to-End Service
From initial design consultation through occupancy, we handle everything:
- Feasibility assessment and cost estimation
- Architectural and structural design
- Permit applications and municipal coordination
- Construction management and inspections
- Code compliance and quality assurance
Turnkey Construction
You don't coordinate multiple trades. We manage framing, electrical, plumbing, HVAC, finishes, and inspections. You get a ready-to-occupy unit on schedule and on budget.
Warranty & Peace of Mind
All T-ROC ADU projects include our comprehensive warranty covering workmanship, materials, and code compliance. You're protected.
Local Market Knowledge
We know Markham's Site Plan Process, Toronto's Pre-Approved Designs, Vaughan's parking requirements, and the GTA's permitting timelines. That expertise saves you months and thousands in unnecessary revisions.
ADU & Garden Suite Service Areas
T-ROC builds ADUs throughout the Greater Toronto Area, including:
- Markham (our headquarters — we know every detail of Markham’s regulations)
- Toronto (East York, Scarborough, North York, Etobicoke)
- Vaughan
- Richmond Hill
- Mississauga
- Brampton
- Ajax & Durham Region
If your municipality isn’t listed, contact us — we may still be able to help.
Frequently Asked Questions About ADUs & Garden Suites
How much does a garden suite cost in Ontario?
A standard garden suite (600–1,100 sq ft) in Ontario typically costs $180,000–$350,000 depending on size, finishes, and site conditions. Custom projects or those requiring underpinning can exceed $400,000. Timeline is 6–10 months. We provide free estimates after site assessment.
Do I need a permit to build an ADU in Markham or Toronto?
Yes, always. Under Ontario law, garden suites and secondary suites are permitted “as-of-right” in most zones (no zoning amendment needed), but a building permit is mandatory. Permits ensure code compliance and protect your investment. T-ROC handles all permitting paperwork and municipal coordination.
How long does it take to build a garden suite in Ontario?
Typical timeline: 3–4 weeks for design, 6–8 weeks for permits (varies by municipality), 4–6 months for construction. Total: 6–10 months from initial concept to occupancy. Basement conversions are faster (3–5 months total).
Can I rent out my ADU or garden suite in Ontario?
Yes. Legal ADUs built to code can be rented. In fact, rental income is one of the biggest benefits. Expect $1,500–$2,500/month for a garden suite in the GTA, generating $18,000–$30,000 annually. Ensure your lease and property tax situation are clear — consult a real estate lawyer.
What size can an ADU be in Ontario?
Size limits vary by municipality. Toronto allows garden suites up to 60 sq m (646 sq ft), while Markham permits up to 100 sq m (1,076 sq ft). Secondary suites in basements or other locations aren’t size-limited, only by your lot and building code. We’ll clarify your specific limits during the consultation.
Will an ADU increase my property taxes?
It may. A legal ADU increases assessed property value. Contact your municipal assessment office about implications. However, the long-term property value increase and rental income typically offset any modest tax increase. Consult a real estate accountant for specifics.
What if my lot is too small for a garden suite?
Consider a basement conversion or garage conversion instead. Most properties can legally add a secondary suite without extensive lot space. We’ll assess your property during the free consultation and recommend the best option for your situation.
Ready to Build Your ADU?
The first step is a free consultation. We’ll assess your property, explain your options (garden suite, basement conversion, garage conversion), outline costs and timelines, and answer all your questions about Ontario’s regulations and Markham’s specific requirements.
Whether you’re looking to generate rental income, house family members, or unlock your property’s potential, we’re here to guide you from concept to occupancy.
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