Fourplex vs. sixplex vs. multiplex: which is right for your lot?

The three categories, in plain English

Fourplex. Four self-contained dwelling units in a single building. The 2023 city-wide bylaw made this the as-of-right baseline on most Toronto residential lots. Typically three storeys, sometimes with a basement unit and/or a garden suite at the rear to push the door count to five or six on a fully developed site. See our fourplex page.

Sixplex. Six units, generally in the same massing envelope as a fourplex but with smaller individual units. Now largely as-of-right in Toronto — for most lots there's no Committee of Adjustment hearing, no public process; the application goes straight to the Building Division like a fourplex does. The building looks much like a fourplex from the street — same height, same footprint — but the per-square-foot economics are different. See our sixplexes page.

Larger multiplex. Seven to twenty units, usually requiring a deeper lot, a corner lot, or an assembly of two adjacent lots. At seven units the building changes category twice at once. On the zoning side, the City treats it as an apartment building — floor space index applies, a constraint fourplexes and sixplexes never face. On the building-code side, you enter a thicket of interlocking decisions where each one moves cost, rentable area, and timeline: elevator or a layout engineered so you don't need one (a fourth storey does not automatically mean an elevator — but avoiding it has to be designed in from the first sketch); sprinklered or not, and what that choice does to your stair and corridor strategy; wood stud, metal stud, or a hybrid structure, each with its own fire-rating, acoustic, and trade-pricing consequences; egress counts; fire-rated corridor design that doesn't eat your rentable floor plate. Get two of those calls wrong in combination and a viable building becomes a marginal one. Most schemes at this scale also need a minor variance or a rezoning on top. This is exactly where we operate — it's the segment we know better than anyone in the city, and frankly it's the segment where you want someone who's already made these trade-offs eleven, thirteen, eighteen units at a time. See our large multiplexes page.

Lot requirements at a glance

These are rules of thumb, not bylaw thresholds — and the frontage numbers are softer than people assume. A sixplex-and-up works on a 25-foot frontage; for the seven-plus-unit buildings we specialize in, depth is what does the heavy lifting. Our project at 91 Barton sits on a 25′ × 160′ lot and carries eleven units. Every lot is its own answer.

How cost actually moves

The instinct is to think of cost on a per-square-foot basis. In our experience that's the wrong unit, because PSF varies wildly across the three programs for reasons that don't show up in a simple comparison:

• Fixed costs amortize differently. Excavation, foundation, roof, mechanical rough-in, and the building permit application have similar absolute costs whether you're building four units or six in the same envelope. A sixplex spreads those over more rental doors, which generally improves PSF.
• Large multiplexes add building-code decisions, not just costs. Once you cross certain unit-count and storey thresholds, the Ontario Building Code shifts you into "Part 3" — and almost nothing in Part 3 is a fixed bill. Elevator vs. an elevator-free layout, sprinklered vs. unsprinklered strategies, wood stud vs. metal stud, how many egress stairs and where — each is a fork where the right answer depends on the lot, the program, and the other forks. The spread between a well-played hand and a default one is enormous, and it's invisible on a PSF comparison.
• Finishes are the variable, not the constant. A four-unit and a sixteen-unit building can have the same kitchen package, the same flooring, the same windows. Finish spec drives a much larger share of cost variation than unit count does.

In rough terms: a fourplex is the smallest total cheque, a sixplex generally produces the best PSF for a small site, and a larger multiplex delivers the lowest land-cost-per-door but the highest absolute capital requirement.

Returns dynamics

Denser is generally better — until it isn't. The reason: rental revenue scales close to linearly with unit count (six units rent for roughly 1.5x what four units rent for), while a lot of the costs scale more slowly than that. So as you move up the density ladder, returns tend to improve.

The constraints that bend this curve:

• Permitting risk. If you need to clear a Committee of Adjustment hearing, you're carrying months of schedule and soft costs that an as-of-right project doesn't. But the risk is smaller than it used to be: under recent provincial reforms, a neighbour can no longer appeal a Committee approval — only the applicant can appeal a refusal. The risk is mostly schedule now, not outcome.
• Construction complexity. Adding an elevator and the structural steel to support a fourth storey doesn't just cost more — it lengthens the build, which compounds carrying cost on the construction loan.
• Lease-up risk. Twelve units don't lease as quickly as four. The vacancy assumption you use in underwriting matters more on the larger building, especially if the lease-up window straddles a soft rental season.

The honest answer — and where we land as builders: denser almost always wins, and the ceiling is usually higher than the lot's owner assumes. A site that looks like a fourplex lot will often carry a sixplex; a sixplex lot, pushed through a variance or sitting on a major street, can frequently carry a true multiplex. The as-of-right fourplex is the floor, not the target. Our work is finding the real ceiling and building to it — because that's where the returns that justify a ground-up development actually live.

We'll be candid about our own bias: the fourplex and the sixplex are rarely where we choose to spend our effort. The economics that move the needle live at the larger end, and most of our work is convincing a lot to give up more than its zoning first suggests it will. Challenging what a "single residential lot" can support is, more or less, the entire point of the company.

Permitting timelines

Rough orientations, all measured from a complete design package to permit issuance, on a typical Toronto site:

• Fourplex or sixplex, as-of-right: months, not quarters. Both are now largely as-of-right in Toronto — no Committee hearing, no public process; the permit application is straightforward and the building official's review is bounded.
• Multiplex with a minor variance: add a Committee of Adjustment hearing cycle. The framing has changed in the applicant's favour: a Committee approval can no longer be appealed by neighbours — only the applicant can appeal a refusal. For what it's worth, we've taken five of our own approvals through appeal and prevailed in all five.
• Large multiplex with rezoning: measured in quarters and sometimes years. Add public consultation, planning staff review, council, and possible appeal.

Carrying cost matters here. A site you've bought at market with a construction loan accruing interest doesn't care whether you're waiting on a permit or a hearing — the meter is running either way. Faster paths are worth real money. (Once shovels are in the ground, our builds run seven to ten months, regardless of which approval path got us there.)

How to think about your specific lot

The decision framework we use, in order of importance:

1. What's the most this lot can support? We start at the ceiling, not the floor. Before defaulting to the as-of-right fourplex, we map what a minor variance, the lot's depth, laneway access, or a Major Streets frontage could actually unlock. The gap between the as-of-right floor and the real ceiling is where the value of a development is created.
2. What does the lot physically support? Frontage, depth, soil, servicing, and tree-cover constraints can rule out programs that look fine on paper.
3. What's your timeline and risk tolerance? A homeowner-developer who wants a finished building in eighteen months is in a different program than an owner who can wait for a rezoning to pay off — and the denser the program, the more that patience is rewarded.
4. How will you hold or exit? Purpose-built rental held long-term and condominium sale are different optimization problems. They lead to different programs even on the same lot.

Where we focus is the larger end — see large multiplexes — though we cover fourplexes and sixplexes too. Our project portfolio includes examples across the range.