Same idea, a dozen names.
ADU, ARU, second suite, in-law suite, garden suite, laneway house: everyone researching this ends up confused by the terminology before they’ve even started. Most of these words describe the exact same thing. Here’s what each one actually means, and which one your municipality uses on the permit application.
9 names. One permit term.
Pick the word you’ve heard. We’ll show you what it means on paper.
ADU
Additional Dwelling UnitThe term most people search for online. Not an official Ontario term: it’s the general label for a second, self-contained home on a property that already has one.
- Who says it
- What people type into Google
- Where it sits
- Anywhere on the lot
- On your permit
- ARU
Learn these two first.
Additional Dwelling Unit
The term most people search for online. Not an official Ontario term: it’s the general label for a second, self-contained home on a property that already has one.
Additional Residential Unit
Ontario’s official term. This is the word your municipality’s zoning bylaw and building permit application actually use.
We use ADU because it’s what people look for, and ARU because it’s what gets typed on your permit.
Interior, attached or detached.
Most location terms fit into one of these three groups.
See the difference in one glance.
Basement apartment
The most common interior unit: a self-contained suite in the basement, with its own kitchen, bathroom, sleeping area and entrance.
Garden suite
A detached unit in the backyard. Does not need to face a public laneway: the general term for a standalone backyard unit. Also called a coach house when it’s built above or beside a garage.
Laneway house / laneway suite
A detached unit specifically on a lot with frontage on a public laneway, accessed from that laneway. A garden suite that happens to face a lane.
Everyday language, same meaning.
Second suite / secondary suite
Everyday term for any additional unit, interior or detached. Interchangeable with ADU or ARU in normal conversation.
In-law suite / granny flat
Same physical thing, described by its use: built or set aside for a parent or relative rather than a paying tenant.
Accessory apartment
Older municipal-bylaw language, now largely replaced by “additional residential unit” in Ontario’s provincial framework.
The words on the paperwork.
- As-of-right
- Allowed under the existing zoning bylaw without a rezoning application or committee hearing. Ontario requires most urban residential lots to permit up to three units (main house, basement suite, garden suite) as-of-right.
- Egress window
- A window or door in a basement bedroom large enough for a person to climb out in an emergency and a firefighter to climb in. A required minimum size under the Building Code.
- Fire separation
- The fire-rated wall and ceiling assembly required between an interior unit and the rest of the house, so a fire in one unit is contained long enough for both households to get out.
- Setback
- The minimum required distance between a building and the property line. Governs whether a garden suite fits, and where.
- Servicing
- Connecting a detached unit to water, sanitary sewer and hydro, usually with its own dedicated connections trenched across the yard. The main reason garden suites cost more than basement conversions.
- BCINBuilding Code Identification Number
- The qualification the person or firm preparing your permit drawings must hold. Ask to see it before hiring anyone.
Pick the question closest to yours.
Basement Apartment vs. Garden Suite
Cost, timeline, zoning path and servicing, compared side by side.
Does my property qualify?
A self-check on space, lot rules and servicing before you call.
For Homeowners
Adding a legal unit to help carry the mortgage, start to permit.
We’ll translate the bylaw for your address.
Which unit types your lot allows, what your municipality calls them, and what the permit will ask for.