What Is a Triplex? Three Units on One Lot

Of all the small multi-unit buildings, the triplex is the one Canadian policy actually chose. When Ontario and British Columbia rewrote their planning rules, three units is the floor they set — which means that on most serviced residential lots in those provinces, a triplex is something you are entitled to build rather than something you have to argue for.

That shift is larger than it sounds, and it is widely misunderstood. This guide explains what a triplex is, what “as-of-right” actually means for a homeowner, what converting a house into three units involves, and how the financing works.

What is a triplex?

A triplex is one building divided into three separate, self-contained dwelling units. Each unit has its own entrance, kitchen, bathroom and living space, and each can be occupied independently of the others. All three sit on a single lot, normally under one owner and one title.

The arrangement varies. A triplex might be three units stacked over three floors, two units up and one down, or a main house with two additional units carved out of the basement and an upper floor. In older Canadian neighbourhoods, a great many triplexes are simply large single-family houses that were converted decades ago — sometimes legally, sometimes not.

Like a duplex, a triplex is one property. You cannot normally sell a single unit without a separate legal process to divide the land or register a strata or condominium.

Triplex vs duplex vs fourplex

The words are a count of units: two, three, four. What differs is the regulatory territory each one sits in.

A duplex is two units. Straightforward, permitted almost everywhere that permits a second unit at all, and financed as an ordinary residential property.

A triplex is three. This is the as-of-right ceiling in Ontario and the floor in much of British Columbia, which makes it the most permissive point in the range — the largest building you can generally proceed with on the strength of the zoning alone.

A fourplex is four. In Ontario the fourth unit usually needs municipal permission beyond the provincial floor, and it loses the automatic development-charge exemption that applies to the second and third units. It gains access to the federal GST rental rebate, which has a four-unit gate. Different trade-offs, covered in our fourplex conversion guide.

Above four, at five units, mortgage financing generally moves from residential to commercial underwriting — a much bigger step than any of the ones below it.

Why three units is the as-of-right number

This is the part worth understanding properly, because “as-of-right” is the single most misunderstood term in Canadian residential development.

What as-of-right actually means

As-of-right means the use is already permitted by the zoning bylaw. You do not need a rezoning, a minor variance, a committee of adjustment hearing, or a council decision. Nobody votes on whether you may proceed.

What it does not mean is that you can start building. You still need a building permit, and your project still has to comply with every objective standard in the bylaw — height, setbacks, coverage, parking — and with the building code. The difference is that compliance is checked rather than debated. If your drawings meet the standards, the permit follows; no one can decline on the grounds that they’d prefer you didn’t.

For a homeowner, this converts the most unpredictable part of a project — discretionary approval, with its hearings, timelines and possible refusal — into a technical review. That is why the reform mattered.

Ontario: three units under Bill 23

The More Homes Built Faster Act, 2022 (Bill 23, Royal Assent November 28, 2022) requires most residential lots to permit up to three units without a rezoning. The configuration can be three units within the primary building, or two within the primary building plus one in an ancillary structure — a laneway or garden suite, for example.

Two details that matter and are often left out. First, this applies to urban residential land served by municipal water and sewer — not to every lot in the province. Second, as BLG and other firms summarising the legislation note, the exemption from development charges and parkland dedication attaches to the second and third units. A fourth unit does not get it automatically.

British Columbia: three to six under SSMUH

The Province of British Columbia’s small-scale multi-unit housing rules under Bill 44 require most municipalities to permit a minimum of three units on parcels of 280 m² or smaller and four on larger parcels, within urban containment boundaries in municipalities over 5,000 people. Near frequent bus service — a stop served at least every 15 minutes on average between 7 a.m. and 7 p.m., Monday to Friday — the minimum rises to six. A further round of changes under Bill 25 is due in local bylaws by June 30, 2026.

Alberta: municipal, and in Edmonton’s case more permissive

Alberta has no provincial equivalent. Edmonton’s Small Scale Residential zone under Zoning Bylaw 20001 permits up to eight units on a sufficiently large mid-block lot, which puts a triplex comfortably inside the envelope. Calgary and other municipalities set their own rules.

The consistent caveat: provincial rules set a floor that municipalities implement in their own bylaws, and the local bylaw is what a building official actually applies. Confirm your address rather than relying on the provincial headline. Our zoning and bylaws guide covers what that check involves.

Converting a house into a triplex

Most Canadian triplexes start as houses. Permission is now the easy part; the building code is where the real work is.

The items that consistently bite:

• Egress from every unit. Each dwelling needs a compliant way out, which for basement units usually means enlarging window openings and sometimes excavating a window well. On upper floors it can mean a second stair.
• Fire separation between units. Rated wall and floor assemblies between all three units and any shared spaces. In an existing house, this generally means opening up floors and ceilings rather than adding a layer.
• Sound separation. Distinct from fire separation, and frequently the thing that determines whether the units are actually rentable at a good price.
• Ceiling height. A common failure in older basements. Gaining height means underpinning or lowering the floor — structural work with structural cost.
• A second means of egress from shared stairs, where your code requires it at three units.
• Servicing and electrical capacity. Three kitchens, three sets of appliances and possibly three meters. A 100-amp service usually will not carry it.
• Parking, where your municipality still requires it — though several have removed minimums, particularly near transit.

Building codes differ by province. Ontario, Alberta and B.C. each set their own requirements for egress, fire separation and sound transmission, and guidance written for one province is not reliable in another.

What does a triplex cost?

We don’t publish a figure, because the honest range is too wide to be useful. A conversion of a large, structurally sound house with good ceiling height is a fundamentally different project from a conversion of a low-basement bungalow, and both differ from a new build.

What drives it:

• Existing ceiling height and structure. The single biggest variable in a conversion. Underpinning changes the budget category.
• Number of new kitchens and bathrooms. Plumbing and ventilation, repeated per unit, is the expensive part.
• Fire and sound separation across three units.
• Electrical service capacity and metering arrangement.
• Servicing. Whether the existing water and sewer connections carry three units.
• Provincial cost base. B.C. charges 7% PST on many construction inputs; Alberta has neither a provincial sales tax nor Ontario-style development charges.

One real, documented saving in Ontario: because the second and third units are exempt from development charges and parkland dedication under Bill 23, a triplex conversion avoids fees that a fourth unit would not automatically escape. On a GTA lot, development charges are a meaningful number, not a rounding one.

How is a triplex financed?

A triplex sits comfortably on the residential side of Canadian mortgage lending. CMHC’s multi-unit insurance programmes begin at five or more self-contained units; at one to four units, a property is generally handled under homeowner mortgage rules.

In practice that means underwriting against your personal income and credit rather than purely against the building’s operating income, with residential rates and amortisations. Lenders will typically consider some portion of projected rental income when qualifying you, though how much varies.

The common routes are refinancing the existing property to fund the conversion, construction financing drawn in stages, or conventional refinancing once the units are complete and tenanted. CMHC’s refinance product for secondary suites, introduced January 15, 2025, supports properties with up to four units to a maximum of 90% of as-improved value, subject to conditions including owner or close-relative occupancy and the funds going to construction rather than being taken out as equity.

Note what a triplex does not get: the federal GST rental rebate requires four or more stand-alone apartments, so three units falls below that gate. Confirm current terms with CMHC or a mortgage professional. Our financing page covers the funding routes in more detail.

Find out whether three units fit your property

Because three units is now permitted as-of-right across much of Ontario and British Columbia, the binding question is usually no longer whether you’re allowed — it’s whether your building can be brought to code economically, and whether your servicing carries three units.

HouseLyft’s free property assessment answers both for your specific address. Our multiplex development page covers the larger end of the range. When you want a straight answer for your own lot, request your free report.