Guide · Updated September 10, 2026
What Makes a Basement Apartment Legal in Ontario — and What Your Municipality Adds
"Legal" means three separate things at once: the Province's Building Code says what the unit must physically be, your municipality's zoning by-law says how many units a lot may carry and where the door can go, and some municipalities then require the unit to be registered or licensed. This guide sets out the provincial floor, then puts the municipal rules we have verified side by side — each row links to the page where the sources are listed.
What the Province requires everywhere
Ontario's Planning Act permits up to three residential units as-of-right on a lot where residential uses are allowed — three in the main building, or two in the main building and one in an ancillary building such as a garage — but only in settlement areas with full municipal water and sewage services. The Province's own regulatory notice says the permission does not reach land on partial or private servicing and names rural areas as the example. Municipalities may allow more than three; they may not allow fewer where the provincial rule applies.
The Ontario Building Code sets the physical standard, and for a second unit in a house more than five years old its retrofit provisions apply. The recurring numbers: a ceiling height of 1.95 metres over the required floor area of the unit (municipal guides commonly allow 1.85 metres under beams and ducts); a 30-minute fire separation between units and between each unit and common areas, reduced to 15 minutes where interconnected smoke alarms serve every unit; a self-closing rated door where the unit opens onto a shared area; a bedroom egress window with 0.38 square metres of unobstructed opening and no dimension under 380 millimetres; interconnected smoke alarms on every level and in each bedroom, and carbon monoxide alarms where there is a fuel-burning appliance or an attached garage; and a compliant exit — a door directly outside, or a shared exit fire-separated from the rest of the house.
A unit that existed on or before 14 July 1994 is treated differently: it is assessed against the Ontario Fire Code's retrofit section 9.8 through a fire department inspection rather than against the Building Code, which is usually a lighter path for a genuinely old apartment and irrelevant for a new one.
What your municipality adds
Above the provincial floor, each municipality decides the unit count on serviced lots, the parking, where an entrance may go, whether a detached unit is allowed and how big, and whether units must be registered. These are the rules we have verified, as of September 2026, from each municipality's own by-law, handout or fee schedule. By-laws are amended often; the linked page for each place lists the consolidation date relied on and every source.
| Municipality | Units permitted | Parking for the unit | Entrance or path rule | Registration or licence | Key by-law |
|---|---|---|---|---|---|
| Milton (serviced) | Up to 3 additional units on a lot with a detached, semi or townhouse (4 total); at most one in an accessory building | 1 space per dwelling unit on the lot | Unobstructed path 1.2 m wide, 2.1 m high from the street line to the unit's entrance | Mandatory, $340 per unit, annual renewal (By-law 032-2025) | 016-2014 s.4.10 (March 2026 consolidation) |
| Milton, rural (Campbellville, Moffat, Brookville) | Outside the Escarpment Plan: 1 unit in the house or an accessory building; inside it, Escarpment Rural Area 1 unit in the house only, none in Natural or Protection areas; accessory-building unit on private services needs 1.5 ha | As urban Milton | As urban Milton; NEC Development Permit first where development control applies | As urban Milton | 144-2003 s.4.25 (By-law 004-2026) |
| Halton Hills (Georgetown, Acton) | 2 on a fully serviced lot: two inside (together ≤60% or 220 m²) or one inside (≤40% or 110 m²) plus one detached (≤40% or 90 m²); a unit wholly in the basement may use the whole basement | 2 for the house plus 1 per unit, 2.75 × 5.5 m, all on one driveway | Detached unit in the interior or rear yard with clear access to the rear yard; no unit on the front | Mandatory before occupancy (By-law 2023-0060): $1,252.54 stand-alone or $262.47 with a permit (2026) | 2024-0098 (in effect 2 January 2025) |
| Mississauga | 2 additional units (two attached, or one attached plus one garden suite) in the RL, RS, R12–R14, R16, RM3, RM5 and RM6 zones; the City states up to 4 units total with its fourplex by-law | None required (Art. 4.1.1.2); one driveway per lot | No placement rule for an attached unit; a garden suite needs a hard-surfaced 1.2 × 2.1 m fire path no more than 45 m from the street | Mandatory, no fee (By-law 114-16); the ARU permit fee is refunded after final inspection | 0225-2007 s.4.1.1 via 0174-2023, amended 0048-2025 and 0114-2025 (June 2026) |
| Oakville | 2 additional units: two attached, or one attached plus one detached in an accessory building | 2 for the house plus 1 per unit; tandem permitted | The unit's entrance may not face a yard narrower than 1.0 m | No registration by-law; a Zoning Certificate of Occupancy is required for a basement-to-suite change of use ($273, 2025) | 2014-014 s.4.1 (consolidated 4 December 2025) |
| Burlington | 3 additional units on a serviced lot (4 total); up to two detached, in one accessory building of ≤80 m² | 0 for the first unit, 1 for the second or third | 1.2 m unobstructed path from the street for a rear or side-yard unit; one exterior entrance per street-facing elevation (By-law 2020) | No registration step; the Occupancy Permit closes the file | 09-2026 s.5.14 (in force 2 March 2026); By-law 2020 outside the LN zones |
| Hamilton (urban) | A single detached house may hold 2 additional units plus 1 detached; a lot is capped at 4 dwelling units; conversion to a fourplex permitted | None in Parking Rate Areas 1–3; 1 per unit elsewhere | 1.0 × 2.1 m path from the street to a detached unit; the 2022 amendments limited front-façade entrances — confirm against the current text | No registry; a Rental Housing Licence in Wards 1, 8 and parts of 14 ($734.86 plus $135, January 2026) | 05-200 s.4.33 (August 2026 posting; 24-051, 25-075) |
| Hamilton, rural (Flamborough) | 1 additional unit inside the house in the A1, A2 and S1 zones; 1 detached unit only on a lot of at least 1.5 ha | Per Section 5 of By-law 05-200 | One entrance on the front façade (By-law 22-132 text); 1.0 m path to a detached unit | Licence as above where the ward applies | 05-200 s.4.33 via 22-132 and 24-039 |
| Waterdown (former Flamborough by-law) | 1 secondary unit inside the house plus 1 detached unit | None additional, provided the spaces that existed on 12 May 2021 are kept | Maximum one entrance on the front façade; no outside stair above the first floor except a required exit | As Hamilton | 90-145-Z via 22-135 (June 2022) |
| Toronto | 4 dwelling units as-of-right on RD, RS and RT lots; 6 in detached buildings in the Toronto and East York district and Ward 23; plus one garden suite or one laneway suite | None for a garden or laneway suite | Fire-access path 1.0 m wide (0.9 m sprinklered or laneway) and 2.1 m high, no more than 45 m from the street | No registration found; building permit and Zoning Applicable Law Certificate | 569-2013 ch.150.7 and 150.8; multiplex amendments May 2023; 654-2025 (June 2025) |
| Cambridge | 2 additional units on urban residential land (3 total): two attached, or one attached plus one detached; none in the Floodway or Floodplain Overlay zones | 1 per unit, may be tandem; no new driveway | Entrance within 30 m of the street; a side-yard door 1.2 m from the lot line; 0.9 × 2.1 m path from a side or rear door to the street | No registration by-law; building permit and occupancy approval | 26-007 s.4.19 (in effect 3 February 2026) |
Where a unit is not allowed at all
Four situations stop a basement apartment before the drawings start. Hazard land and floodplain: Milton's by-law prohibits additional units on land a conservation authority identifies as hazard land or regulatory floodplain unless the authority specifically permits it, and Cambridge's by-law bars them outright in the Floodway and Floodplain Overlay zones. The Niagara Escarpment: in Milton's rural area no unit is permitted in the Escarpment Natural or Protection areas, and where the Commission's development control applies its permit comes before the municipality's. Private services: Burlington allows additional units only on a parcel of urban residential land, meaning municipal water and sewer; Halton Hills requires a detached unit on a septic lot to share the house's system with an assessment showing it can; Milton's rural by-law and Hamilton's rural zones allow units on private services with a servicing test. Zoning that excludes the lot: standard condominium townhouses in Mississauga, Rural and Open Space zones in Hamilton, lots under Cambridge's transition rules still governed by the old by-law.
None of these is obvious from the street. They are why the first thing we do on any address is pull the zone, the conservation authority's map and, where it applies, the Escarpment Commission's map — before anyone measures a room.
Registration, licensing and legalizing an existing unit
Where a municipality registers units — Milton, Halton Hills, Mississauga — the unit is not legal until it is on the registry, and renting an unregistered one carries fines: Milton's run from $500 to $50,000 with a $600-a-day administrative penalty, Mississauga's up to $25,000 for an individual and $50,000 for a corporation, Halton Hills' up to $50,000 for an individual. Burlington, Oakville, Toronto and Cambridge rely on the building permit and occupancy record instead; Hamilton has no registry but licenses rental units in three wards.
An existing, unpermitted apartment can usually be made legal, and the path depends on its age. A unit that existed on or before 14 July 1994 is inspected against the Fire Code's retrofit section through the fire department; anything newer is inspected against the Building Code, with the retrofit compliance alternatives available to a house more than five years old. Expect upgrade work — separation, alarms, egress, sometimes headroom — and a permit for that work before registration. Halton Hills' process, described on the Georgetown page, is typical: municipal law enforcement checks zoning and property standards, then fire or building inspectors depending on the unit's age.
How this plays out on a real house
The order matters. Zoning first — the unit count, the parking, whether the lot is even eligible. Then the measurements that decide feasibility: the ceiling under the lowest beam or duct against 1.95 metres, the side yard against the path rule, the driveway against the parking count. Then the separate entrance, which is where most projects physically start and which HMH builds in three days once the permit is in hand: excavation, stairwell, opening, door, drain and waterproofing. Then the suite behind it — separations, alarms, egress, kitchen, bath — through inspections to occupancy, and the registration package where the municipality requires one.
Our multi-unit conversion stories in Hamilton show what the middle of that process looks like on century houses; the separate entrance versus walkout guide covers the first physical step in detail.
Sources this guide relies on (11) →
- ero.ontario.ca/notice/019-8366
- www.haltonhills.ca/work/development/additional-residential-units
- www.mississauga.ca/wp-content/uploads/2024/05/29163554/by-law-0174-2023.pdf
- www7.mississauga.ca/Departments/PB/ZoneBylaw/DZBR1/Part%204%20-%20General%20Provisions.pdf
- www.oakville.ca/getmedia/ae93a884-590a-46bc-8a05-070522d8357f/zoning-by-law-2014-014-part-
- www.burlington.ca/en/planning-and-development/resources/Zoning-Clearance-Certificates/Zoni
- www.hamilton.ca/sites/default/files/2026-08/zoningby-law05-200-section4-generalprovisions-
- www.hamilton.ca/sites/default/files/2024-04/24-039.pdf
- www.hamilton.ca/sites/default/files/2022-07/22-135.pdf
- www.toronto.ca/city-government/planning-development/planning-studies-initiatives/multiplex
- media-003-ca.cdn.govstack.com/cambridge-ca/media/jhijomn5/certified_26-007-zba.pdf
Questions This Guide Answers
How many units can I legally have in my house in Ontario?
At least three on a serviced lot in a settlement area — that is the provincial as-of-right rule — and more where your municipality allows it. Milton and Burlington permit three additional units (four total), Hamilton caps a lot at four with fourplex conversions permitted, Toronto allows four as-of-right and six in parts of the city, and Mississauga states up to four with its fourplex by-law. Oakville, Halton Hills and Cambridge sit at two additional units. The table above has the by-law for each.
Do I need a parking space for a basement apartment?
It depends entirely on the municipality. Mississauga requires none for an additional unit; Toronto requires none for a garden or laneway suite; Burlington requires none for the first unit; Hamilton requires none in Parking Rate Areas 1 to 3. Milton requires one space per dwelling unit, and Halton Hills, Oakville and Cambridge require one per additional unit on top of the house's own — Cambridge and Oakville allow it to be tandem. Every municipality limits you to the existing driveway or one driveway per lot.
How high does a basement ceiling need to be for a legal apartment?
1.95 metres over the required floor area of the unit under the Ontario Building Code's second-unit provisions, and municipal guides such as Milton's allow 1.85 metres under beams and ducts. That is roughly six feet five. Many pre-1970s basements miss it by a few centimetres, and whether the height can be recovered by reworking ducts and bulkheads or only by lowering the floor is the first thing we measure.
Do I have to register my basement apartment?
In Milton, Halton Hills and Mississauga, yes — the unit is not legal until it is registered, and Milton and Halton Hills charge a fee while Mississauga does not. Oakville requires a Zoning Certificate of Occupancy for the change of use rather than a registration. Burlington, Toronto and Cambridge rely on the building permit and occupancy approval. Hamilton has no registry but requires a Rental Housing Licence for rented units in Wards 1, 8 and parts of 14.
What is the fine for an unregistered basement apartment?
Where registration is mandatory, it is steep. Milton's registration by-law sets fines from $500 to $50,000 and a first administrative penalty of $600 a day. Mississauga's fines run to $25,000 for an individual and $50,000 for a corporation. Halton Hills exposes an individual renting an unregistered unit to a fine of up to $50,000. Beyond the fine, an unregistered unit is a problem at sale, at insurance renewal and in any dispute with a tenant.
Can I have a basement apartment on a septic system?
Sometimes. The Province's three-unit permission does not apply to private services, so the municipality decides. Burlington does not permit additional units on well and septic at all. Halton Hills allows a detached unit on a septic lot only if it shares the house's system and an assessment shows the system can serve both. Milton's rural by-law allows a unit on private services with a septic evaluation, and requires 1.5 hectares for a unit in an accessory building. Hamilton's rural zones allow one unit inside the house with a servicing test.
My basement apartment has been there for years. Can I make it legal?
Usually, yes. If it existed on or before 14 July 1994 and you can show that with leases, tax records or affidavits, it is inspected against the Fire Code's retrofit section through the fire department. If it is newer, it is inspected against the Building Code, with a house more than five years old able to use the retrofit compliance alternatives. Expect some upgrade work — fire separation, interconnected alarms, egress windows, occasionally headroom — under its own permit, and then registration where the municipality requires it.
Does a legal basement apartment need its own entrance?
It needs its own compliant exit, and a separate exterior entrance is the cleanest way to provide one. The Building Code also accepts a shared exit that is separated from the rest of the house by a 30-minute fire separation with interconnected smoke alarms in every unit and the common area. Municipal zoning then decides where the door may go — Oakville bars an entrance facing a yard under 1.0 metre, Cambridge and Milton set path widths, Waterdown and Burlington limit front-facing entrances — which is why the door usually ends up on the side or the rear.