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Secondary Suites
Secondary Suites designed, permitted and built across the 30 municipalities of the Greater Toronto Area - zoning review, permit drawings and construction handled by one team.
Secondary Suites - Overview
Key Takeaways
- Key features: Main-floor, upper-level and above-garage units, Second-unit registration with the municipality, Sound and fire separation between units
Secondary suites carved out of an existing house - main-floor, upper-level or above-garage units built to the Ontario Building Code second-unit standard.
Features & Specifications
- Main-floor, upper-level and above-garage units
- Second-unit registration with the municipality
- Sound and fire separation between units
- Kitchen, bath and laundry rough-ins
- Parking and entrance compliance review
Key takeaways
- Secondary suites are Ontario's legal category for a second self-contained dwelling inside an existing house - a regulatory classification, not a physical style. A basement apartment, a converted upper floor and a rear addition all qualify.
- What makes it a secondary suite is the definition, not the location: independent kitchen, bathroom, sleeping area and its own means of egress, registered as a distinct dwelling unit.
- Compliance is where these projects succeed or fail - fire separation of the required rating, interconnected smoke alarms across both units, carbon monoxide detection, egress per sleeping room, and an entrance that does not pass through the other dwelling.
- Because Bill 23 permits three units, a secondary suite and a detached garden or laneway suite can generally coexist on the same lot - which is how owners reach two rental incomes from one property.
Secondary suites are what Ontario legally calls a second self-contained dwelling inside an existing house - a regulatory category rather than a physical style. A basement apartment is a secondary suite. So is a converted upper floor, a rear addition with its own door, and a unit carved out of an oversized main floor. What makes it a secondary suite is not where it sits but that it satisfies the definition: independent kitchen, bathroom, sleeping area and its own means of egress, registered as a distinct dwelling unit.
This is the form owners search for when they want the paperwork right rather than the renovation pretty. The provincial framework is O. Reg. 299/19 on additional residential units, amended in November 2024, layered over Bill 23 - the More Homes Built Faster Act (2022) - which requires Ontario municipalities to permit up to three residential units as-of-right on most lots already holding a detached, semi-detached or townhouse dwelling on full municipal services. Before Bill 23, most second units required a rezoning application taking six to twelve months, with no guarantee of approval. That bottleneck is gone; the Building Code requirements are not.
What this includes
- Registered as a distinct dwelling unit under O. Reg. 299/19, not finished as an unpermitted apartment
- Rated fire separation between dwellings with interconnected smoke alarms and CO detection in both units
- Compliant egress window or second exit serving every sleeping room, plus minimum ceiling height verified before quoting
- Entrance independent of the other dwelling, designed as a side, rear or walk-out access
- Retroactive legalisation assessment for suites a previous owner built without a permit
- Bill 23 three-unit planning - secondary suite and a detached garden or laneway suite on the same lot
- ESA electrical filing and inspection on all new circuits and the second kitchen supply
- Low end of the $40K-$450K ADU cost span, against $200K-$350K for a detached 500-600 sq ft unit
Compliance is where secondary suite projects succeed or fail. Every unit needs a fire separation of the required rating between dwellings, interconnected smoke alarms across both units, carbon monoxide detection, a compliant egress window or second exit serving each sleeping room, minimum ceiling height, and an entrance that does not pass through the other dwelling. Electrical work is filed with the ESA. Where a suite is created inside an existing house, the work is renovation-class, so HCRA builder registration and Tarion enrolment generally do not apply - though we confirm that classification project by project instead of assuming it.
Who builds them: owners financing a mortgage with rental income, multigenerational families, and investors legalising a unit that a previous owner built without a permit. That last case is common in Brampton, Mississauga and Scarborough, and it is the one where an honest assessment matters most - an unpermitted suite is uninsurable, and a fire claim on one is a catastrophe.
Cost sits at the low end of the ADU category, which spans $40,000 to $450,000 overall, far below the $200,000 to $350,000 a detached 500-600 sq ft unit costs in the GTHA. Permit review runs four to eight weeks. Because Bill 23 permits three units, a secondary suite and a detached garden or laneway suite can generally coexist on the same lot - which is how owners reach two rental incomes from one property.
Secondary Suites - 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.
Secondary suites carved out of an existing house - main-floor, upper-level or above-garage units built to the Ontario Building Code second-unit standard. Concretely that means: main-floor, upper-level and above-garage units; second-unit registration with the municipality; sound and fire separation between units; kitchen, bath and laundry rough-ins. One contract covers design, permit and construction, so there is no handoff between a designer and a builder halfway through.
Related service: Our ADU services
On a 700 sq ft reference unit our estimate band runs $91,000-$147,500 in Brock up to $95,500-$155,000 in East York - roughly $383 to $402 per square foot. The spread is not a markup: this work involves no new envelope - the money goes into fire separation, egress windows, ceiling height and a second kitchen, and the per-municipality difference comes from approval fees, frost depth and snow load. Final pricing follows a site visit.
Related service: Our ADU services
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: Our ADU services
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 no new envelope - the money goes into fire separation, egress windows, ceiling height and a second kitchen, 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: Our ADU services
Ready to Get Started?
Ready to start your secondary suites project? Send us your address and we will tell you what your lot allows, what it costs and how long the permits take.