Building Types | Triplex
Building a Triplex in Ottawa
A triplex is three dwelling units in one building. Three units is exactly Ontario's Bill 23 as-of-right floor, so a triplex is permitted on any serviced residential lot without a rezoning. Ottawa's By-law 2026-50 goes one unit higher, to four — which makes the triplex-versus-fourplex call a question of what fits.
When a Triplex Beats a Fourplex
When a fourplex will not fit
If lot area, frontage, or the size envelope caps you at three units to the zone standards, a triplex is the as-of-right form that actually fits — no variance needed.
When the third unit is the easy one
Adding a garden suite to a duplex reaches three units without rebuilding the main house. The fourth unit may need far more work for less return.
When you want to clear the Bill 23 floor cleanly
Three units is the provincial baseline. A triplex hits it without leaning on Ottawa's extra fourth-unit allowance.
The fourth unit is not free. It needs the lot area, the frontage, and the size envelope to fit to the zone standards. When those run out at three, a triplex is the form that stays as-of-right. Run the feasibility check before you decide three versus four.
Three Common Triplex Configurations
Three stacked units
One unit per floor over three levels. Common on narrow lots where you build up rather than out. Each unit gets its own entry, often off a shared stair.
Two in main + one ancillary
Two units in the main building plus a garden or laneway suite in the rear. This is the configuration Bill 23 explicitly names as meeting the three-unit floor.
Side-by-side plus a unit
A side-by-side pair with a third unit carved from a basement or upper level. Works when the lot is wide enough for two ground-floor doors.
The "two in main plus one ancillary" form is the one Bill 23 names directly — two units in the main building plus a garden or laneway suite counts as the three-unit floor (More Homes Built Faster Act, 2022). If you already own a house with a buildable rear yard, that is often the cheapest path to three units.
Where the Triplex Sits in Ottawa's Rules
Ottawa's Neighbourhood (N) zones replaced the old building-type R-zones with size-based zones. The base N1 zone allows up to four units, and the count climbs in N2 and N3 (City of Ottawa zoning). A triplex sits under all of those caps, so the unit number is rarely the limit — the lot's size envelope usually is. Check your zone and standards on geoOttawa before you design around three units.
Best For
- ✓ Lots that fit three units cleanly but cap out before a fourth to the zone standards.
- ✓ Owners adding a garden suite to a duplex to clear the Bill 23 three-unit floor.
- ✓ Builders who want the full provincial as-of-right count without depending on the extra Ottawa unit.
Usually Fails When
- ✕ The lot easily supports four units — you may be leaving a unit of value unbuilt.
- ✕ Your lot is on septic or partially serviced, which limits units before the zoning does.
- ✕ Frontage or lot area is too small to fit even three units without a minor variance.
What To Verify Before Spending Money
- → Your lot is fully serviced with municipal water and sewer.
- → Your N-zone and its lot-area, frontage, height, and coverage standards on geoOttawa.
- → Whether your chosen triplex form fits the size envelope, or whether four would fit just as well.
Frequently Asked Questions
Can I build a triplex in Ottawa as-of-right?
What is the difference between a triplex and a fourplex in Ottawa?
How can I configure a triplex on a narrow Ottawa lot?
Is a triplex a multiplex in Ottawa?
Official Sources Referenced
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