A-506 Additions & New Builds
Houses converted to legal multiplexes in Toronto
A multiplex conversion turns one house into two to four legal units. Toronto has allowed up to four units on residential lots city-wide since 2023, and conversions typically cost $150,000 to $700,000.
- Typical cost
- $150,000–
$700,000 - Timeline
- 3–5 months (duplex)
- Permit
- Yes, building permit
- Prices checked
- 2026
- In-house engineering and permits
- Free on-site estimate
- MKC Guarantee: on time, within budget
Free, no-obligation estimate. We typically reply within 24 hours.
A-506.1 Why MKC
Why choose MKC for legal multiplexes
Each unit in a multiplex needs its own kitchen, bathroom, exit and fire separation, so a conversion is mostly work you won’t see: rated floors and walls, new stairs, plumbing stacks, and heating and power for every unit. Our engineering department prepares the drawings and files the permit, and the same company builds it. We only use ECRA/ESA-licensed electrical contractors to perform any electrical work. That work is done under an ESA permit.
Up to four units, without rezoning
Since May 2023, Toronto’s zoning has permitted multiplexes of up to four units city-wide. Fiveplexes and sixplexes are allowed only in Toronto and East York District and Ward 23. The City charges no development charges on the second to sixth unit in projects of up to six units.
A-506.2 Scope
What’s included
- A-506.1Feasibility and zoningUnit count, exits, ceiling heights and zoning checked against your house before design starts.
- A-506.2Drawings and permitsArchitectural and structural drawings and the building permit application, prepared in-house.
- A-506.3Fire and sound separationRated floor, ceiling and wall assemblies between units, with protected exits and smoke alarms.
- A-506.4Kitchens and bathroomsA full kitchen and bathroom for each unit, with plumbing by a City-licensed plumbing contractor.
- A-506.5Heating, cooling and powerSeparate systems for each unit by a contractor with a City heating licence, and upgraded electrical service.
- A-506.6Basement and entrancesBasement units, new walkout entrances and, where the ceiling is too low, underpinning.
A-506.3 Cost guide
What it costs
in Toronto & the GTA
Converting a Toronto house to two to four units typically costs $150,000 to $700,000, renovation only. Additions and underpinning are extra.
House of 1,800–2,800 sq ft converted to 2–4 units; no addition or underpinning
Toronto reviews complete permit applications within 10 business days for a house with up to two units, and 15 business days for three or more. A duplex conversion takes about three to five months to build. Triplexes and fourplexes take longer, and we set the schedule in writing.
Every project is different, so your estimate comes with its own written schedule, and we aim to beat the usual industry timeline on every job.
| Level of work | Typical cost |
|---|---|
| Duplex (2 units)A second unit created inside the house, usually in the basement. | $150,000– |
| Triplex (3 units)Three self-contained units with fire separations, extra kitchens and bathrooms and upgraded services. | $250,000– |
| Fourplex (4 units)Four units, with new stairs and exits and separate mechanical systems for each unit. | $400,000– |
| Fourplex with a major additionFour units plus a rear or third-storey addition to make room for them. | $700,000– |
| Item | Typical price |
|---|---|
| Conversion construction cost, GTA | $250– |
| Rated floor and ceiling between units | $8– |
| Fire separation assemblies, whole building | $25,000– |
| Plumbing for four units | $35,000– |
| New basement walkout entrance | $12,000– |
Worked examples
- Example 1
Detached Toronto house made a duplex by legalizing the basement
$100,000–$280,000 - Example 2
Design, engineering, permits and other soft costs on a fourplex conversion
$48,000–$126,000 - Example 3
Fourplex with full basement underpinning and an addition (and up)
$1,000,000–$1,500,000
What moves the number
- 01Number of units
A duplex runs $150,000 to $280,000, a triplex $250,000 to $420,000 and a fourplex $400,000 to $700,000, because each unit adds a kitchen, bathroom and exit.
- 02The basement
A legal basement suite is usually the first added unit. If the ceiling is too low, underpinning adds $50,000 to $120,000 on a footprint of about 1,000 sq ft.
- 03Fire and sound separation
Rated assemblies across the building cost $25,000 to $60,000. Floors and ceilings between units run about $8 to $14 per sq ft of floor.
- 04Separate services
Plumbing for four units runs $35,000 to $80,000, and heating and cooling for four units $25,000 to $70,000.
- 05Additions and soft costs
An addition to fit the fourth unit moves the total to $700,000 and up. Design, engineering, permits and insurance take 12% to 18% of the budget.
Rebates, subsidies and tax credits
- No charge on units 2 to 6City of Toronto development charge exemption for additional units
No development charges on the second to sixth unit in developments of up to six units, in effect July 24, 2025, where provincial law does not already exempt them. The owner must show the City that the project qualifies.
Program rules - Up to 90% of improved valueCMHC Refinance for building secondary suites
Insured refinance through a CMHC-approved lender for owner-occupied properties with up to 4 units. The as-improved value must be below $2,000,000, the new unit must be self-contained and it cannot be rented for periods under 90 days.
Program rules - Up to $7,500Multigenerational Home Renovation Tax Credit (federal)
15% of up to $50,000 of qualifying costs when the work creates a self-contained unit so a senior (65 or older) or an adult eligible for the disability tax credit can live with a qualifying relative. Your own labour does not count; keep contracts and invoices.
Program rules - Loan up to $125,000City of Toronto Home Energy Loan Program (HELP)
Low-interest City loan for energy work such as heat pumps, insulation and windows, repaid on the property tax bill. For Toronto houses and low-rise buildings up to six units; lender consent is needed. 2026 fixed rates are 3.83% to 5.12%, plus a 2% charge.
Program rules
Renovation-only totals with soft costs and permits, before HST. They leave out the purchase price, additions, underpinning and financing. Triplex and fourplex totals rest on one published source. Prices checked in 2026. Not a quote: your estimate is built from your own measurements and choices.
Where these numbers come from
- Multiplex Conversion (building permit application guide), City of Toronto (2026)
- Expanding Housing Options in Neighbourhoods, City of Toronto, City Planning (2026)
- Building Permit Fees, City of Toronto (fees effective January 1, 2026)
- Building Permit Review Streams, City of Toronto (2026)
- Development Charges Overview, City of Toronto (2026)
- CMHC Refinance for Building Secondary Suites, CMHC (2026)
- Multigenerational Home Renovation Tax Credit, Canada Revenue Agency (2024)
- Home Energy Loan Program, City of Toronto (2026)
- Building By-law Schedule “B”: 2026 Classes of Permits and Fees, City of Mississauga (2026)
- Published 2026 price guides and GTA contractor price pages (2026)
G-003 How we work
How we deliver your multiplex conversion
- 1
Free Estimate
Tell us what you have in mind. We review your space and goals and give you a clear estimate at no cost.
- 2
Design + Permits
Our in-house designers model your project in 3D so you can see it and settle every choice. Our in-house engineering team prepares drawings, engineering letters and permit applications.
- 3
Material Procurement
We order cabinets, tile, stone, pavers and decking from trusted suppliers such as Unilock, Techo-Bloc, TimberTech and Trex, and schedule deliveries around the work.
- 4
Construction Process
Our crews build to code with site supervision and regular updates, so you always know where things stand.
- 5
Project Completion
Final inspection, walkthrough and clean-up. On time, within budget and beyond expectations. That is the MKC Guarantee.
Plan your project
with a free estimate.
We review your space and goals and give you a clear estimate at no cost.
A-506.4 Questions
Questions about legal multiplexes
Don’t see your question? Call (647) 637-6052 or ask in your estimate request.
How much does a multiplex conversion cost in Toronto?
Typical cost in Toronto and the GTA: $150,000 to $700,000 (House of 1,800–2,800 sq ft converted to 2–4 units; no addition or underpinning). By level of work: Duplex (2 units): $150,000 to $280,000; Triplex (3 units): $250,000 to $420,000; Fourplex (4 units): $400,000 to $700,000; Fourplex with a major addition: $700,000 to $1,200,000. The number of units moves the price most, because each one adds a kitchen, a bathroom, an exit and fire separation. The basement, separate heating and plumbing, and any addition come next. These are typical ranges, before HST, with prices checked in 2026; your estimate is built from your own measurements and choices.
How many units can I have on my lot?
Up to four in one building on residential lots across Toronto, under the zoning changes Council adopted in May 2023. Five and six units are permitted only in Toronto and East York District and Ward 23. The building still has to meet the zoning for height, setbacks and lot coverage, and we check those for your address before design.
Do I need a building permit to convert my house?
Yes. The City of Toronto requires a building permit to convert a house to a duplex, triplex, fourplex, fiveplex or sixplex. In 2026 the fee is $11.53 per square metre of interior alterations, $18.56 per square metre of new floor area and $56.33 for each new unit. For a 2,400 sq ft house converted to four units with no addition, that is about $2,740 before plumbing and HVAC permit fees.
Will I pay development charges?
For most conversions, no. Toronto’s development charges by-law exempts the second to sixth unit in developments of up to six units, in effect since July 24, 2025, where provincial law does not already exempt them. The owner has to show the City that the project qualifies. We put that paperwork in with the permit application.
Can the basement become one of the units?
Often, and it is usually the first unit added. A legal basement unit on its own costs about $90,000 to $150,000. If the ceiling is too low, the floor can be lowered by underpinning or bench footing, which needs an engineer and its own permit drawings. We measure the ceiling height and look at the drains on the first visit.
What if tenants live in the house now?
Tell us early. Tenants have rights under Ontario’s Residential Tenancies Act when work needs their unit empty, and Toronto has its own rules for some rental renovations. We check which apply to your house before the permit application goes in, because they affect both the schedule and the budget.
Can I finance a conversion through my mortgage?
Possibly. CMHC insures refinancing of up to 90% of the as-improved property value to add units, on owner-occupied properties with up to four units and a value below $2,000,000. It is arranged through a CMHC-approved lender, and the new units cannot be short-term rentals. The lender, not MKC, decides approval and terms.
Can I see my multiplex in 3D before work starts?
Yes. We model each unit in 3D with its layout, stairs and entrance, so you can see how the units share the house and approve the plan before the drawings are finished.
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