Multiplex Toronto | Duplex, Triplex & Fourplex Design

Multiplex Housing in Toronto: Duplex, Triplex & Fourplex Design

By Sara Rahgozar, M.Arch, OAA – Principal, Quadrant Architects

What can you legally build on a residential lot in Toronto today?

In most neighbourhoods, a detached house can now contain up to four residential units. That means many Toronto homeowners can convert a house into a duplex, triplex, or fourplex without a rezoning application – a significant shift in what’s possible on a standard residential lot. Quadrant Architects designs and permits multiplex buildings across Toronto. We’re licensed by the Ontario Association of Architects (OAA) and work with the specific constraints of Toronto’s Zoning Bylaw 569-2013 — lot coverage, angular plane, setbacks, and Ontario Building Code fire separation requirements – on every project we take on.

Key Terms: What Each Housing Type Means

Duplex – a residential building containing exactly two self-contained dwelling units under one roof, each with its own kitchen, bathroom, and entrance.
Triplex – a single building with three separate residential units, each legally self-contained and meeting Ontario Building Code egress and fire separation standards.
Fourplex – a residential building with four dwelling units; the maximum permitted as-of-right under Toronto’s current residential zoning in most zones.
As-of-right zoning – a permitted use that does not require a rezoning application, Committee of Adjustment hearing, or minor variance; the project complies with existing zoning rules as written.
Missing middle housing – medium-density residential building types (duplexes, triplexes, fourplexes, townhouses) that sit between detached houses and high-rise apartments. Toronto’s zoning reforms specifically target this housing type to address the gap in the city’s housing supply. When planners, media, and developers refer to ‘missing middle housing in Toronto,’ they mean the same category of buildings this page covers.
Residential intensification – the process of increasing the number of dwelling units on an existing residential lot through conversion, addition, or new construction.

2026 POLICY UPDATE – TORONTO HOUSING LEGISLATION

Two overlapping pieces of legislation govern multiplex permissions in Toronto:
Ontario Bill 23 (More Homes Built Faster Act, 2022) – provincial legislation directing municipalities to permit up to three residential units as-of-right on most residential lots. Applies across Ontario including all GTA municipalities.

Toronto EHON (Expanding Housing Options in Neighbourhoods) – Toronto’s own zoning bylaw amendment, going beyond Bill 23 to permit up to four units as-of-right. Applies within the City of Toronto boundary only – not to Mississauga, Markham, Vaughan, or other GTA municipalities, which operate under their own by-laws.

If your property is outside Toronto’s city limits, we confirm applicable municipal permissions during the feasibility review.

Where Are Multiplexes Permitted in Toronto?

The City of Toronto amended its Zoning Bylaw in 2023 – following Ontario’s Bill 23 – to permit up to four residential units in all residential zones city-wide. This includes the RD (Residential Detached) zones that cover most of Toronto’s low-rise neighbourhoods: areas like Leslieville, Riverdale, the Danforth, the Annex, East York, High Park, Scarborough, and Etobicoke that were previously limited to single-family houses.

In practical terms: if your property sits in a residential zone in Toronto, it likely qualifies for a multiplex conversion or new build without triggering a rezoning or minor variance application. The as-of-right permissions have removed much of the approval risk that previously made these projects slow.

That said, individual properties vary. What determines what’s actually buildable on a specific lot:

Lot size and frontage – minimum dimensions apply per zone designation
Existing building footprint, structural condition, and ceiling heights
Parking requirements – reduced or eliminated near transit corridors, but not everywhere
Setback and lot coverage restrictions specific to the zone
Heritage designation or proximity to a Heritage Conservation District
Servicing capacity – water, sewer, and electrical connections for multiple units

A proper feasibility review is the only way to confirm what your specific property can support. That’s the first thing we do on every multiplex project.

When a Multiplex May Not Be Feasible on Your Property

Not every Toronto property can support a multiplex. Before investing in design, these are the conditions that typically disqualify a site or significantly constrain the project:

Lot width under 6 metres (approximately 20 feet) – most fourplex configurations require more frontage to meet setback requirements on both sides
Lot depth under 30 metres – shallow lots restrict unit layout options; rear yard setback requirements eat into buildable area, sometimes making a three-unit configuration more realistic than four
Existing structure with ceiling heights under 1.95 metres in the basement – legal basement units require minimum ceiling height; older bungalows often don’t meet this without underpinning
No rear lane or limited rear yard depth – affects garden suite eligibility and rear access for parking
Active heritage designation – may restrict exterior alterations, additions, or demolition
Inadequate servicing – properties on older water or sewer mains may require upgrades that affect overall project economics

What Designing a Multiplex Actually Involves

Multiplex design is more involved than dividing a house into units. Every project has to satisfy zoning, building code, and livability requirements simultaneously – and the decisions made early in design have significant cost implications later.

Zoning Compliance

We review the specific zoning designation and overlay conditions for your property before any design begins – angular plane restrictions, maximum building height, rear and side yard setbacks, and the permitted Floor Space Index (FSI). On a recent four-unit multiplex conversion in East York, the angular plane requirement measured from the rear property line was the binding design constraint – it limited the third-floor massing in a way that a lot coverage or FSI calculation alone would not have revealed. Getting this right before concept design prevents permit rejections and avoids costly redesigns mid-process.

Ontario Building Code: Part 3 vs. Part 9

Multiplexes with more than two units, or buildings exceeding certain area thresholds, fall under Part 3 of the Ontario Building Code rather than the more permissive Part 9 that governs detached houses. Part 3 triggers more rigorous fire separation, egress, and structural requirements. We design to the correct code path from the start – not as a revision after the permit examiner flags it.

Unit Layouts and Livability

Each unit needs to function as a real home: adequate natural light, minimum ceiling heights, accessible egress windows, and private outdoor space where the site allows it. A well-designed fourplex commands better rents and appraises higher than one squeezed together purely to hit the unit count. We’ve seen the difference play out in resale values.

Parking and Servicing

In many Toronto neighbourhoods with good transit access – particularly those within 500 metres of a subway station or 800 metres of a light rail stop – parking requirements for multiplex buildings are reduced or eliminated. We confirm this in the feasibility phase, since parking determines whether a three-storey fourplex is even achievable on the lot.

Structural and Mechanical Coordination

Multiplex projects typically require structural engineering (for new builds or significant additions), mechanical and plumbing coordination for separate unit services, and sometimes geotechnical reports. We coordinate these consultants and integrate their requirements into the permit drawings – so the submission is complete on first review rather than triggering rounds of additional information requests.

Common Mistakes Homeowners Make When Planning a Multiplex

Most multiplex projects that run into trouble do so before design begins. The issues we see most often:

Starting without feasibility: Assuming the lot qualifies without a proper zoning check.
Underestimating servicing costs: Adding two or three units to a property often means upgrading water, sewer, and electrical connections to handle the increased load. These costs are real and can reshape the project economics significantly.
Treating conversion and new build as equivalent: Converting an older house into a triplex is sometimes the right call. But older structures often have framing, ceiling height, or foundation conditions that make a new purpose-built multiplex more cost-effective over a 10-year horizon. We look at both paths honestly.
Ignoring parking rules until late in design: In areas where parking requirements aren’t waived, surface parking can consume lot area that would otherwise support the unit count. Discovering this after layouts are drawn means redesigning from scratch.
Using the wrong code path: Permit drawings for a building with three or four units fall under Part 3 of the Ontario Building Code. Drawings prepared to Part 9 standards – appropriate for single-family homes – will be rejected at submission.
Not stress-testing the financial model: Permit timelines, contractor availability, and material costs shift. Projects designed to a budget from 18 months ago may not pencil out today. We flag this in the feasibility phase.

A thorough feasibility review addresses all of these before any design fees are committed. It’s the most efficient use of time and money on a multiplex project.

How to Convert a House to a Multiplex in Toronto

When homeowners ask how to convert a house into a multiplex in Toronto, the process breaks down into seven stages – from confirming what zoning permits on your specific lot through to construction. Here’s the sequence:

Confirm as-of-right eligibility – verify that your property’s zoning designation permits the number of units you want without a variance or rezoning application. This requires reviewing the specific zoning bylaw conditions for your lot, not just the general city-wide policy.
Commission a feasibility study – an architect reviews lot dimensions, existing building conditions, servicing capacity, parking requirements, and heritage constraints to determine what’s realistically achievable and at what approximate cost.
Develop concept designs – layout options exploring unit configurations, floor plans, and building massing. For conversions, this typically involves two to three schemes that trade off unit size against unit count.
Retain required consultants – structural engineer, mechanical engineer, and sometimes a geotechnical engineer and energy modeller depending on project scope. Your architect coordinates these.
Prepare and submit permit drawings – a complete building permit set including architectural drawings, structural drawings, and required supporting documentation. Submitted to the City of Toronto’s Building Division.
Respond to examiner comments – the city’s permit examiner reviews the submission and may issue a Zoning Review or Building Code deficiency list. Your architect responds with revised drawings or written clarifications.
Receive building permit and begin construction – once the permit is issued, construction can begin. Your architect remains available for site questions and to review contractor requests for information (RFIs).

Why Toronto Homeowners Are Converting to Multiplexes

The financial case for multiplex development has strengthened as Toronto’s rental market has stayed persistently tight and mortgage carrying costs have increased. The most common reasons clients pursue these projects:

Rental income from additional units to offset mortgage payments
Long-term property value – multi-unit buildings are appraised on an income basis, often significantly above equivalent single-family market value
Housing family members or adult children while maintaining privacy between units
Estate planning – creating income-producing assets within an existing property rather than selling
Reducing reliance on a single income stream in an uncertain economic environment

The as-of-right zoning changes have reduced the approval risk that previously made these projects slow or unpredictable. For straightforward conversions or new builds on qualifying lots, the permit process is more predictable than it was three years ago – though permit review timelines at the City of Toronto still run 8 to 16 weeks for complete submissions on typical residential intensification projects.

Multiplex vs. Garden Suite: Which Is Right for Your Toronto Property?

Many Toronto homeowners qualify for both – a multiplex in the main building and a garden suite in the backyard. They’re different products serving different needs. Here’s how they compare:

	Multiplex (Duplex / Triplex / Fourplex)	Garden Suite
Location	Within the main building on the lot	Detached structure in the backyard
Max Units (Toronto)	Up to 4 units as-of-right under EHON	1 unit; can combine with multiplex in main building
Lot Requirement	Minimum width and depth apply per zone	Rear yard access required; minimum setbacks from all property lines
Typical Use	Rental income, multigenerational living, long-term investment	In-law suite, rental unit, home office, guest accommodation
Construction Type	Conversion of existing house or purpose-built new build	New detached construction only
OBC Code Path	Part 3 (3–4 units) or Part 9 (2 units)	Part 9 typically; size and configuration dependent
Permit Complexity	Moderate to high depending on unit count and scope	Moderate; rear yard access and servicing are key variables
Can You Have Both?	Yes - a triplex plus a garden suite is possible on many standard Toronto lots	Yes - additive, not exclusive to a multiplex

Many properties support both – a triplex in the main house plus a garden suite can create four or five units on a standard 25-foot lot. We assess the full potential of each property during the feasibility review.

Frequently Asked Questions About Multiplexes in Toronto

Q: Can I turn my Toronto house into a fourplex?
A: In most cases, yes. Toronto’s 2023 zoning bylaw amendment permits up to four residential units on most residential lots city-wide – including the RD zones that cover the majority of the city’s detached housing stock. Whether your specific property can support four units depends on lot size, existing building conditions, servicing capacity, and zone-specific setback requirements. A feasibility review typically takes one to two weeks and confirms what’s achievable before any design fees are committed.

Q: Do I need an architect to build a multiplex in Toronto? 
A: For buildings with more than two units, or where the project falls under Part 3 of the Ontario Building Code, an architect is required to stamp and seal the permit drawings. Even for two-unit duplexes, working with an OAA-licensed architect substantially reduces permit rejection risk – drawings prepared without understanding Toronto’s specific zoning bylaw requirements and OBC compliance standards are frequently deficient. An architect also coordinates structural and mechanical consultants, manages permit submissions, and responds to city examiner comments, which homeowners managing this independently often underestimate.

Q: How long does it take to get a multiplex building permit in Toronto?
A: Permit review for a straightforward residential intensification project with a complete submission typically runs 8 to 16 weeks at the City of Toronto Building Division. Projects involving heritage properties, Committee of Adjustment variances, or complex structural conditions take longer. The most common cause of extended timelines is an incomplete initial submission – examiner comments require revised drawings, which reset parts of the review clock. We prepare submissions specifically to minimize the frequency and number of deficiency responses.

Q: How much does it cost to design a multiplex in Toronto? 
A: Architectural fees for multiplex design are typically structured as a percentage of construction value or a fixed fee based on project scope. A duplex or triplex conversion of an existing house will have different fee implications than a purpose-built fourplex new construction. We provide a clear fee proposal once we’ve reviewed the property and confirmed the project scope – we don’t quote fees before understanding what’s actually involved.

Q: Can I convert my property into a multiplex? 
A: Up to four units are now permitted as-of-right in many Ontario municipalities. We confirm zoning compliance before starting design.

Q: What’s the difference between a multiplex conversion and a new build in Toronto? 
A: A conversion involves adapting an existing house into multiple units – adding separate entrances, separating mechanical systems, and meeting fire separation requirements within the existing structure. A new build demolishes the existing structure and constructs a purpose-built multiplex from scratch. Conversions are often less expensive upfront but can be constrained by existing ceiling heights, framing, and foundation conditions. New builds offer more design flexibility and typically result in better long-term livability across all units. We assess both options during feasibility and give you a realistic comparison.

Q: What neighborhoods in Toronto work best for multiplex projects? 
A: The as-of-right permissions apply across the city, so neighbourhood matters less than property-specific conditions. Lots with lane access, adequate width, good transit proximity (which affects parking requirements), and no heritage constraints tend to be the best candidates regardless of location. We’ve completed multiplex projects and feasibility studies in East York, Scarborough, Etobicoke, the Annex, Leslieville, Riverdale, along the Danforth, and in High Park – the property conditions vary more by lot than by neighbourhood.

Q: How much rental income can a Toronto multiplex generate?
A: Rental income depends on unit size, location, configuration, and current market conditions. A duplex conversion produces one additional rental unit; a fourplex can generate three separate rental income streams simultaneously. In many Toronto neighbourhoods – Leslieville, Riverdale, East York, along the Danforth – three-bedroom units command rents that, combined, can offset a significant portion of the carrying costs on the property. The financial model depends heavily on construction cost, financing terms, and achievable rents for your specific location and unit mix. We can speak to realistic unit configurations during the feasibility review; a mortgage broker or financial advisor is the right person to model the returns.

Start With a Multiplex Feasibility Review

Before designing a duplex, triplex, or fourplex, you need to know what your property can legally support. We review zoning, lot conditions, servicing, and building constraints to determine what’s realistically achievable – before any design fees are committed. Contact Quadrant Architects to book a feasibility review for your property.

Meet Our Team

Every member of our team has advanced education in architecture and design

What’s Clients Say

I’ve had the great pleasure of collaborating with Studio Quadrant on several projects, interior and architectural design for 3 town house, 4 semi-detached and my own detached house in Ottawa. Studio Quadrant, the driving force behind the firm has a unique way of balancing environmental stewardship, great design, and realistic budgets. They never cease to impress me with their ability to come up with ideas on unique design, weaving them together in beautiful, creative ways. The studio’s attention to detail doesn’t stop at design, they stay with the project through construction and add real value to the process. They made working together enjoyable and brought an intense committed work ethic to the team. I look forward to our next opportunity and highly recommend them to those who are looking for a fresh take on their projects. They will bring ideas to the table that have real meaning.

Studio Quadrant designed my modern, new house in Scarborough Bluffs. The final product is above an beyond expectations! Studio Quadrant was creative, detailed and thorough. They also helped during the committee of adjustment process, and the result was more than my expectation. Studio Quadrant designs were very creative and responded directly to my needs. and I would highly recommend them to others looking for both commercial and residential architecture and interior services, and I would pass their information on to friends and family without hesitation.

We were particularly excited about the creative solutions from Farzad, which were always developed anew on the basis of our ideas. Right the first planning distinguished itself by an excellent and individual design. The various 3D display variants always gave us a very detailed feeling for the planned living space. The adjustment and coordination during the planning process was always a pleasure – despite the distance (from Germany), we experienced simplicity here. The matching, consulting, and tuning of the plans was possible any time and was characterized by a high level of engagement and absolute flexibility. Thank You Farzad!!