What Is a Basement Apartment? Ontario and the GTA, Explained

In Ontario the below-grade rental is a “basement apartment” — not a basement suite, which is the Alberta and BC term. The vocabulary difference matters when you go searching for rules, because you’ll land on the wrong province’s code.

Ontario is also the jurisdiction where the permission question has largely been settled. Since Bill 23, most serviced residential lots must permit up to three units without a rezoning. What remains is the building code, and that’s where basement apartment projects actually succeed or fail.

What is a basement apartment?

A basement apartment is a self-contained dwelling unit occupying the below-grade level of a house, capable of being lived in independently of the main home.

Self-contained means the four elements: its own kitchen, its own bathroom, a sleeping area, and an entrance that doesn’t require passing through the main dwelling. Miss any one and it isn’t a second dwelling unit — it’s finished basement space.

In Toronto, secondary suites are governed by Section 150.10 of Zoning By-law 569-2013, and in residential zones one secondary suite is generally permitted within a dwelling unit in a detached house, semi-detached house or townhouse, subject to the performance standards in that section.

Are basement apartments legal in Ontario?

Yes — and the permission is unusually strong.

Under the More Homes Built Faster Act, 2022 (Bill 23, Royal Assent 28 November 2022), most residential lots zoned for a single home must permit up to three residential units as-of-right: three within the primary building, or two within it plus one in an ancillary structure. This applies to urban residential land served by municipal water and sewer.

As-of-right means no rezoning, no committee of adjustment, no council decision. It does not mean no permit — you still need a building permit, and your project still has to meet every objective zoning standard and the Ontario Building Code. The difference is that compliance is checked rather than debated.

There’s also a real financial consequence: the second and third units are exempt from development charges and parkland dedication. In much of the GTA, development charges per unit are substantial, so that exemption is often worth more than any grant programme in other provinces ever paid out.

A fourth unit does not automatically get the exemption, and is a municipal question rather than a provincial entitlement.

What makes one legal

The Ontario Building Code items, in the order they tend to matter.

Ceiling height

The OBC permits a minimum finished ceiling height of 1.95 m in basements — notably lower than the 2.1 m required on upper floors — over the required floor area. Beams, ducts and bulkheads may drop to 1.85 m in places.

This is usually the make-or-break measurement, because raising it means underpinning the foundation or lowering the slab. Measure first, before you commission any drawings.

Egress

Every bedroom needs an egress window or door. The OBC sets the minimum unobstructed openable area at 0.35 m² with no dimension less than 380 mm, and the sill no more than 1.5 m above the floor.

Note that 1.5 m sill height is more permissive than some other provinces allow, which is worth knowing if you’re reading guidance written elsewhere.

Below grade, meeting this usually means enlarging the opening — cutting concrete — and often excavating a window well with proper drainage.

Fire separation

New construction requires a minimum 45-minute fire-resistance rating between units.

Existing homes more than five years old get meaningful flexibility: the OBC permits either a 30-minute or 45-minute separation depending on the specific circumstances of the house and the alarm arrangement.

That five-year provision is a genuine Ontario advantage for anyone converting an older house, and it’s frequently overlooked. It can materially reduce what the separation work costs. Establish which route your house qualifies for before pricing the job.

Sound transmission, alarms and electrical

A second unit also triggers sound transmission requirements between units, interconnected smoke alarms, carbon monoxide alarms, and an ESA electrical permit for the electrical work. A second kitchen commonly means a service capacity review.

Permits and registration in Toronto and the GTA

A building permit is required for interior alterations to add a second dwelling unit to an existing house. Toronto is explicit that this work has historically often been done without City review — which is precisely why so many existing GTA basement apartments are unpermitted.

In Toronto, applications go through Toronto Building’s online services. The suite must be permitted by the zoning bylaw and comply with both the Building Code and the Fire Code. Toronto Fire maintains specific guidance for two-dwelling-unit houses, and inspections form part of the process.

Across the wider GTA, the process differs by municipality. Some operate registration or licensing regimes for second units in addition to permits; others rely on permits and inspections alone. Mississauga, Brampton, Markham, Vaughan, Oakville, Oshawa and the rest each run their own systems, and fees and requirements vary.

The practical advice: call your municipality’s building department before you design anything. One conversation establishes what your specific municipality requires, and it’s faster than reading. Our Toronto building guide covers the City process in more detail, and our zoning and bylaws guide covers what’s being assessed.

On grants, be accurate. Ontario has no provincial homeowner basement apartment grant. The Home Efficiency Rebate Plus (HER+) closed to new applicants in February 2024; its replacement, Home Renovation Savings, funds energy efficiency rather than suite construction. Peel Region’s “My Home” programme has been on hold since its pilot ended in June 2024. The federal $80,000 loan was cancelled.

What it costs and earns

We don’t publish a figure. The gap between a basement that already has the height and one needing underpinning is wide enough that a single number misleads.

What drives cost: ceiling height and whether underpinning is needed; enlarging egress openings below grade; the separate entrance, where a shared stairwell won’t serve; fire and sound separation; and electrical capacity for a second kitchen.

What offsets it: the development charge exemption on the second and third units, which in the GTA is a meaningful figure — look up your municipality’s DC rate schedule to see what you’re avoiding.

On rent: a below-grade unit rents for meaningfully less than an equivalent above-grade one. Quality matters more below grade — light, sound separation and a private entrance move the number materially. And any projection ignoring vacancy, maintenance and tax on rental income isn’t one.

One tax point worth raising before you build: creating a self-contained suite is generally a structural change, which can affect how the principal residence exemption applies to the rented portion when you sell. Worth an accountant’s time up front.

Landlord basics

Briefly, because this is a construction guide rather than a tenancy one.

Renting a basement apartment in Ontario makes you a landlord under the Residential Tenancies Act, with the obligations that carries — a written tenancy agreement using the province’s standard lease form, rules on rent increases, and a defined process for ending a tenancy. Rental income is reportable, and you may deduct a proportional share of property expenses.

These rules are detailed, they change, and getting them wrong is expensive in a different way from getting the code wrong. Read the province’s own guidance or take advice before your first tenant moves in, rather than after.

Find out whether your basement can carry a legal apartment

Ceiling height, egress and servicing decide this, and all three are measurable before you spend anything.

HouseLyft’s free property assessment establishes what your property supports and what bringing a unit to code would involve. Our secondary suites overview covers the category more broadly. When you want an answer for your own address, request your free report.