In Toronto, multiplex is the zoning term for a residential building holding two, three or four separate dwelling units, and duplex, triplex and fourplex are just the names for how many units are inside. Two units make a duplex, three a triplex, four a fourplex, and the city files all of them under the single category of multiplex.
There is one more condition in the definition. At least one unit has to sit entirely or partly above another. Units arranged side by side instead of stacked are treated as a townhouse or a semi-detached house, which answer to different zoning standards. This is where everyday language and the by-law part ways. Plenty of buyers say duplex when they mean two homes joined by a shared wall. Toronto's zoning by-law means two units in one building, one above the other.
Where you can find these buildings widened considerably in 2023, when council permitted up to four units across every low-rise residential neighbourhood, covering the R, RD, RS, RM and RT zones. A house already standing in one of those zones can be converted to hold two, three or four units as well. Council went further in June 2025 and permitted six units in nine wards, mostly in the older core, while leaving the remaining wards able to opt in through the chief planner. If you are weighing a specific address, it is worth confirming what the zoning actually permits rather than assuming.
The unit count also decides how you pay for the place. CMHC insures an owner-occupied two-unit purchase on the same footing as a single-family home, meaning five per cent down on the first 500,000 dollars and ten per cent on the balance, with the price capped below 1.5 million dollars. At three or four units the minimum rises to ten per cent of the full price. Buyers who will not live in the building are looking at 20 per cent down instead. Homeowner mortgage insurance stops at four units, so a fifth unit pushes the purchase into commercial lending.
One structural point surprises people. A multiplex is usually one property on one title, so individual units cannot be sold off separately unless the building has been registered as a condominium.
Related reading: What Makes a Basement Apartment Legal in Toronto?, What Is a Laneway Suite and Can You Build One in Toronto?, and Can You Use Rental Income to Qualify for a Mortgage in Canada?
