How Many Units Per Lot in Ontario? Three by Law, Four in Some Cities
Since November 28, 2022, Ontario law lets most urban lots with full municipal water and sewer hold up to three homes. Several cities now allow four, and Toronto allows six in parts of the city. The catch: “allowed as of right” means you skip the rezoning, not the setbacks, the fire route, the sewer capacity or the Building Code.
At a glance
Provincial numbers are a floor, not a ceiling. Your town can allow more; it can’t allow fewer on a qualifying lot.
On a “parcel of urban residential land” (inside a settlement area, zoned residential, on municipal water and municipal sewer), Ontario allows up to 3 units: three in the house, or two in the house plus one in a backyard building. Toronto, Mississauga, Barrie and Kitchener allow up to 4. Rural lots on well and septic follow local zoning, usually one added unit.
What Bill 23 Actually Says, In Plain English
Bill 23, the More Homes Built Faster Act, 2022, took effect on Royal Assent on November 28, 2022. It changed the Planning Act so that on qualifying lots, a town’s zoning by-law can’t stop up to three residential units, even if the by-law doesn’t list them. The government’s own summary is on the Environmental Registry, notice 019-6197.
The lot has to pass three tests. It must be in a settlement area (a town, village or urban area in the official plan). Residential use must be a permitted use. And it must be serviced by both municipal water and municipal sewage. A lot with town water and a septic tank does not qualify. Neither does a cottage on a lake with a well.
On a lot that passes, you get one of two layouts:
- Three units in the house (detached, semi or townhouse), with no unit in any backyard building; or
- Two units in the house plus one unit in a backyard building, which is the garden suite, coach house or laneway suite.
Notice what’s missing. The provincial rule does not guarantee two backyard units, and it does not guarantee a garden suite on a lot with no house. Cities can allow those. The province just doesn’t force them to.
The Local Rules Your Town Is No Longer Allowed to Use
Three rounds of provincial changes stripped out the most common reasons ARUs used to get refused. These apply only to qualifying urban serviced lots.
| Rule | What changed | Source and date |
|---|---|---|
| Number of units | Up to 3 units permitted as described above | Bill 23, in force Nov 28, 2022 |
| Parking | A town cannot require more than 1 parking space per additional unit | Bill 23, Nov 28, 2022 |
| Minimum unit size | Towns cannot set a minimum size; only the Building Code applies | Bill 23, Nov 28, 2022 |
| Development charges and parkland | None on a 2nd or 3rd unit in the house, or a 2nd unit in a backyard building, where the house has no more than 2 units | Bill 23, Nov 28, 2022 |
| Angular planes and FSI | Zoning angular plane and floor space index limits no longer apply to ARU parcels | O. Reg. 299/19 amendments, decision Dec 4, 2024 |
| Lot coverage | At least 45% coverage for all buildings on an ARU parcel | O. Reg. 299/19 amendments, Dec 4, 2024 |
| Minimum lot size | No extra lot size rule just because the lot has ARUs | O. Reg. 299/19 amendments, Dec 4, 2024 |
| Building separation | A town can’t require more than 4 m between the house and the ARU building | O. Reg. 299/19 amendments, Dec 4, 2024 |
| Setbacks | A proposal within 10% of a required setback is allowed without a minor variance, on urban residential lands outside the Greenbelt (not hazard, shoreline or rail-adjacent lands) | O. Reg. 545/06 amended, decision Nov 24, 2025 |
Last checked October 2026 · Sources: ERO 019-6197, ERO 019-9210 (O. Reg. 299/19 amendments), ERO as-of-right 10% variation
Do the arithmetic on that 10% rule before you get excited. A 1.5 m rear setback becomes 1.35 m. That’s 15 cm. It rescues a design that’s a hair over; it doesn’t rescue a design that ignored the setback.
Where You Can Have Four (or More)
A lot of Ontario cities have gone past the provincial three. These are the ones we checked on their own official pages this month.
| Municipality | Units allowed (as the city states it) | Detail worth knowing |
|---|---|---|
| Toronto | Four-unit multiplexes citywide; six-unit multiplexes in Toronto and East York District and Ward 23 (adopted June 2025) | Garden suites are allowed in most residential zones. DC exemptions cover developments of up to 4 units; parkland exemption up to 5 units. Multiplex page |
| Mississauga | Fourplexes as of right on low-rise residential lots citywide (approved Dec 7, 2023) | Up to three storeys, including a partly above-grade basement unit. City release |
| Barrie | Up to four residential units per lot, so up to three ARUs plus the house | 1 parking space per ARU, at least 5.5 m by 2.7 m, stacked or tandem allowed. City page |
| Kitchener | Up to four dwelling units on residential lots | A backyard home can hold 1 or 2 of them. Some lots get fewer because of width, servicing or hazards. City page |
| Burlington | Applications for one, two or three ARUs on a property | The main home needs 2 parking spaces, the first ARU needs none, each extra ARU needs one. City page |
| Guelph | One or two ADUs in a detached structure | One water meter per property. City page |
Last checked October 2026 · Sources: municipal pages linked in each row. Other towns: check with your town.
Watch the fourth unit. The provincial development charge exemption covers the 2nd and 3rd units. Some cities extend it (Toronto exempts up to four units), some use grants instead, and some may charge. Ask for a written DC estimate before you design unit number four. More in our development charges guide.
On Well and Septic, the Province Steps Back
This is the part most province-wide articles skip, and it’s where we build. If your lot is on a private well, a septic system, or both, it is not a parcel of urban residential land. The three-unit guarantee does not apply, and neither do the 2024 relief rules on coverage, angular planes and separation. The province said so plainly in the O. Reg. 299/19 decision.
On those lots your local zoning by-law decides. Many townships allow one additional unit, either in the house or detached, with a maximum distance from the main house and a septic review. Some still use the temporary garden suite route under section 39.1 of the Planning Act. Ottawa’s coach house page, for example, limits rural lots on private services to one additional unit.
The real limit out here is usually the septic bed, not the by-law. A system sized for a three-bedroom house does not quietly absorb a second kitchen and bathroom. You may need a bigger tank, a bigger bed, or a second system, and a designer has to prove it fits on the lot with the required clearances to the well. That design work goes through our partner at SepticReplacement.ca, and our septic guide walks through it.
Farm lots: up to two ARUs
In prime agricultural areas, Ontario’s ARU guidance for prime agricultural areas lets municipalities permit up to two ARUs on a lot where a house is allowed. If you have two, at least one must be inside or attached to the main house. Each must be close to the house or farm building cluster, have proper sewage and water, and meet the Minimum Distance Separation formulae from livestock barns. They can’t be severed off. The Greenbelt and Oak Ridges Moraine plans are stricter. See garden suites on a farm.
Find out how many units your lot can really hold
Send us your address and survey. In 48 hours you get a $399 + HST lot report: unit count, size and setback limits, servicing, fire route and the costs that usually get missed. The fee is credited toward plans or a build.
“As of Right” Is Not “Anything Goes”
The province took away the reasons to say no to the use. It left almost every reason to say no to the building. These are the eight that stop projects on lots that are “allowed” three or four units.
Setbacks and height
Still in the zoning by-law, still enforced. Toronto’s Committee of Adjustment refused a garden suite in 2026 for being 10 cm over the height limit, among other things.
Fire department access
Toronto wants a clear path 1.0 m wide and 2.1 m high, no more than 45 m from the street to the suite door. Many side yards fail this.
Sewer and water capacity
Towns can still require upgraded laterals or meters, and Barrie says the owner pays for service upgrades. See servicing costs.
Trees
City tree by-laws protect large trees, including your neighbour’s tree whose roots cross your yard. A tree permit can take longer than the building permit.
Conservation authorities
Near a creek, ravine, shoreline or floodplain, a conservation authority permit comes first, and some lots get no ARU at all.
The Building Code
Each unit needs its own fire separation, exits, smoke and CO alarms. The 2024 Code gives some relief for houses with up to two secondary suites; past that, expect a stricter review.
Heritage and site-specific rules
Heritage districts and site-specific by-laws can still add design limits. Check the zoning map, not just the general zone.
Registration
Some cities require ARUs to be registered, with fees and penalties. Brampton, for example, runs a garden suite registration process.
How Many Units Per Lot? Five Ways to Count Them Wrong
Counting the existing basement apartment as zero
If the house already has a legal second unit, it counts. A garden suite would be unit three, and a fourth unit only works where the city allows four.
Assuming town water means urban rules
The test is municipal water and municipal sewer. Plenty of Simcoe County lots have one without the other, and they fall under local zoning.
Planning two backyard units under provincial rules
The province guarantees one unit in a backyard building. Two is a city choice, as in Kitchener and Guelph. Read your by-law before you draw a duplex garden suite.
Forgetting the main house still needs its parking
The one-space cap is for the added units. The main house may still need its own spaces, and Burlington, for one, still wants two for the main home.
Thinking more units means more lots
Extra units stay on one title. You can’t sever the garden suite off and sell it. The value shows up as rent, family housing or a higher appraisal, not a second deed. See resale value.
Financing note: CMHC’s refinance product for adding suites covers properties with up to four units in total. If you’re planning unit five somewhere that allows six, that’s a different conversation with your lender. See CMHC secondary suite refinance.
Three units on paper. How many on your lot?
The by-law gives you a number. Your setbacks, sewer, trees and fire route decide whether you can use it. We check all of that in a $399 + HST report, delivered in 48 hours.
Units Per Lot, Answered
How many units can I build on my lot in Ontario?
If your lot is in a settlement area, zoned residential, and on both municipal water and sewer, Ontario law allows up to three units: three in the house, or two in the house and one in a backyard building. Some cities allow four or more. On rural lots with a well or septic, your local zoning by-law decides, and one added unit is common.
Does Bill 23 allow four units per lot?
No. Bill 23 set the provincial floor at three units on qualifying urban lots. Four units comes from city by-laws. Toronto, Mississauga, Barrie and Kitchener are examples that allow four, and Toronto allows six-unit multiplexes in Toronto and East York District and Ward 23.
Can I have a basement apartment and a garden suite?
On a qualifying urban lot, yes. Two units in the house (the main home plus the basement unit) and one unit in a backyard building is one of the two provincial layouts. You still have to meet setbacks, height, fire access and Building Code rules for each unit.
Does the three-unit rule apply to rural properties?
Not automatically. It only applies to lots on full municipal water and sewage in a settlement area. Lots on private well or septic follow the local zoning by-law, and septic capacity is usually the real limit. On prime farmland, provincial policy lets towns allow up to two ARUs, with at least one in or attached to the house.
How much parking does an ARU need?
A town cannot require more than one parking space per additional residential unit on a qualifying lot. Some require none. Burlington, for example, requires zero for the first ARU and one for each extra ARU. Barrie requires one per ARU, at least 5.5 m by 2.7 m, and allows tandem spaces.
Do I pay development charges on a garden suite?
Under Bill 23, no development charges or parkland fees apply to a second unit in a backyard building where the house has no more than two units. A fourth unit may be treated differently depending on the city. Toronto exempts developments of up to four units. Ask your town for a written estimate.
Can my town refuse a garden suite if three units are allowed?
It can refuse a design that breaks zoning or the Building Code. Setbacks, height, fire access, tree protection, conservation authority rules and servicing all still apply. What it can no longer do on a qualifying lot is say the use itself is not permitted, require more than one parking space per unit, or set a minimum unit size.
Can I sever the garden suite onto its own lot?
Generally no. Additional units stay on the same title as the main house. Toronto states that a severance separating a garden suite from the main house is not permitted, and the provincial farm ARU guidance says the same for agricultural lots.