Converting a Garage to a Garden Suite in Ontario: What’s Worth Keeping
A garage already has a roof, walls and a slab, so converting it feels like a head start. Sometimes it is. But a garage was built to keep a car dry, not a person warm, and the slab, footings, walls and the distance to the lot line all get judged again as if it were a new home.
At a glance
Changing a garage into living space is a change of use. That alone triggers a permit, even if you don’t move a wall.
Yes, you can usually convert a garage into a legal garden suite in Ontario. A detached garage becomes the one unit allowed in a backyard building on an urban serviced lot; an attached garage becomes a unit in the house. You need a building permit, and the conversion has to meet today’s Building Code for foundation, insulation, fire separation, exits and windows. The slab and footings decide whether it’s a conversion or a rebuild.
The Zoning Answer Is Usually Yes. The Building Answer Is “Show Me”.
On a lot in a settlement area with full municipal water and sewer, the Planning Act changes from Bill 23 allow up to three units, including one unit in a building ancillary to the house (see the provincial summary). A detached garage is an ancillary building. So the use is generally permitted. Some cities make it easy on purpose: Burlington publishes a Garage Conversion Kit for turning a garage into a separate dwelling unit.
An attached garage is different. Once it’s living space, it’s part of the house, so it counts as one of the units in the house. That’s fine for a second unit. It changes the arithmetic if you were also planning a garden suite out back.
Then comes the building. Toronto’s permit page lists changing a building’s use as needing a permit even with no construction. A garage is not a dwelling, so turning it into one means it has to meet the Building Code for a dwelling. Nothing about the old garage is grandfathered just because it’s already standing.
Seven Places a Garage Falls Short of a Home
We open up a lot of garages. These are the items that decide the budget, in roughly the order we find them.
The footings
Many detached garages, especially older ones, sit on a thickened-edge slab or shallow footings. That’s acceptable for an unheated garage. A heated home needs a foundation that won’t heave with frost, which usually means proper footings below frost depth or a designed frost-protected shallow foundation. If the existing footings can’t be confirmed, expect a designer or engineer to want a test hole.
The slab
Garage slabs slope to the door, usually have no insulation or vapour barrier, and are often cracked. To make it a floor you can live on, you either build up an insulated floor on top, which eats ceiling height, or break it out and pour a new insulated slab with a soil gas barrier. Some cities require soil gas protection outright; Guelph, for example, requires it on detached ADUs over 20 m².
The walls and roof
Typical garage walls are 2×4 with no insulation, and the roof may be trusses that were never designed for an insulated ceiling, drywall weight or snow drift against a new addition. Everything gets insulated and air-sealed to current energy rules, and the heating has to be sized with a heat loss calculation. A BCIN designer such as OntarioHeatLoss.ca does that part.
Distance to the lot line
Garages are often built tight to the side or rear lot line. As a garage that may have been fine, or legal non-conforming. As a dwelling, the Code’s spatial separation rules limit or ban windows in a wall close to the line and can require a fire-rated wall and non-combustible cladding. And zoning may want a bigger setback for a dwelling than it did for a garage. This is the item that kills the most conversions.
Windows and exits
Bedrooms need a window that can be used to get out in a fire, and the unit needs a proper exit door. The big garage door opening usually gets framed in with a wall, a door and windows, which is a chance to fix this and a structural job in its own right.
Plumbing to the sewer
Drains have to run downhill. If the garage floor is lower than the sewer connection, or the run is long, you may need a pump. Trenching across a driveway and yard for water and sewer is often the single biggest line in the budget. See servicing costs.
Fire separation, smoke and CO alarms
For an attached garage, the wall between garage and house was built to keep exhaust out. Now it separates two homes, and the 2024 Building Code’s rules for houses with secondary suites apply, including interconnected smoke alarms and carbon monoxide alarms. For a detached garage, the fire department still needs to reach the door: Toronto, for example, wants a path 1.0 m wide and 2.1 m high, no more than 45 m from the street (City guide).
Have a garage and a hunch?
Send us photos, the survey and a rough sketch. We reply with a fixed quote for a permit package that covers the drawings, site plan and heat loss, so you know what the conversion needs before anything gets torn out.
When Keeping the Garage Costs More Than Losing It
Here’s the honest part. By the time you’ve replaced the slab, underpinned or rebuilt the footings, reframed the door opening, re-insulated every wall, reworked the roof and trenched in the services, the original garage you’re “keeping” may be some studs and a few sheets of roof sheathing. Sometimes the walls aren’t worth saving either.
The thing that’s actually valuable about an old garage is often not the lumber. It’s the location. If it sits where zoning would still allow a dwelling, with a clear fire route, a short run to the sewer and no big trees in the way, you’ve already got the hard part of a garden suite: a buildable spot.
| Signs it’s a good conversion | Signs it’s a rebuild |
|---|---|
| Footings confirmed below frost depth, slab sound | Floating slab, frost cracks, doors that stick every February |
| Meets dwelling setbacks with room for windows | Within a metre or so of the lot line on the side that needs windows |
| Roof can take insulation and drywall, or is easy to replace | Undersized or modified trusses, sagging ridge |
| Short, downhill run to the sewer or septic | Long run under a paved driveway, or below the sewer |
| Ceiling height to spare after an insulated floor | Already low; an insulated floor would put you under code height |
| Clear fire path to the street | Only route is a narrow side yard with a meter and an AC unit in it |
Last checked October 2026 · Builder checklist. Rules source: ontario.ca: Add a second unit and your local building department
Rule of thumb: if the footings and the lot-line distance both pass, convert. If either fails, price a new garden suite on the same spot before you commit, because you’re probably building one anyway. Our cost calculator gives a starting number.
The Parts People Forget to Ask About
You’re losing parking
A town can’t require more than one space per additional unit on a qualifying lot. But the main house may still need its own required spaces. Burlington, for example, requires two for the main home, none for the first ARU and one for each extra ARU. If the garage was holding your required parking, the driveway now has to.
Development charges
Under Bill 23, no development charges or parkland fees apply to a second unit in an ancillary building where the house has no more than two units. Building permit fees and any registration fee still apply. See development charges.
Going up instead of in
A unit above the garage, the traditional coach house, keeps your parking. But the garage walls and footings now carry a whole second floor, and the height limit for backyard buildings applies. Expect a structural review, and often new footings.
Attached garage, family use
Converting an attached garage into a suite for a parent can qualify for the federal Multigenerational Home Renovation Tax Credit if the unit is self-contained. See the credit explained.
Converting a Garage to a Garden Suite, In the Right Order
Confirm the use and the unit count
Is your lot on full municipal services? How many units does the house already have? Run the Rules Checker or read units per lot.
Get the survey out
Measure the garage to the lot lines. Compare with your town’s setbacks for a dwelling in an accessory building, not for a garage.
Dig one test hole
Find out what the footings really are before anybody draws a floor plan. It’s a few hours with a shovel and it decides the whole project.
Plan the services route
Where do water, sewer and hydro come from, and what do they cross? On a septic lot, have the system checked through SepticReplacement.ca.
Design, heat loss and permit
Drawings, site plan, energy and heat loss go in together. Our permit packages bundle these with each stamped piece done by the right BCIN holder.
Build in sequence
Foundation and slab, services, framing and door infill, windows, insulation, inspections. Book the insulation inspection before the drywall shows up.
Find out if your garage is a head start or a teardown.
Our $399 + HST lot report checks zoning, setbacks, the fire path and servicing for your exact lot, in 48 hours. The fee is credited toward permit plans or a build.
Garage Conversions, Answered
Can I convert my garage into a rental unit in Ontario?
Usually yes, on a lot with full municipal water and sewer, because Ontario allows one unit in a building ancillary to the house. You need a building permit, and the conversion must meet the Building Code for a dwelling. Rural lots on well or septic follow local zoning. Short-term rentals have their own city rules.
Do I need a permit to convert a garage into living space?
Yes. Changing a building’s use from garage to living space needs a permit even if no walls move, and most conversions also involve structural, plumbing and heating work that need permits on their own. Zoning must be met too.
Is a garage conversion cheaper than building a new garden suite?
Sometimes. If the footings are below frost depth, the slab is sound and the garage meets dwelling setbacks, you save on foundation and framing. If the slab, footings or lot-line distance fail, you end up rebuilding most of it, and a new suite on the same spot can cost about the same.
My garage is close to the property line. Can it still be converted?
Maybe, but this is the most common deal-breaker. As a dwelling, the Building Code limits or bans windows in walls near a lot line and can require a fire-rated wall. Zoning may also need a larger setback for a dwelling than for a garage. Check both before you design.
Will I need extra parking if I convert my garage?
A town cannot require more than one parking space per additional unit on a qualifying lot, and some require none. But the main house may still need its own required spaces, so if the garage was providing them, the driveway has to. Burlington, for example, wants two for the main home and none for the first ARU.
Do I pay development charges on a garage conversion?
Under Bill 23, no development charges or parkland fees apply to a second unit in an ancillary building where the house has no more than two units. Permit fees still apply, and some cities charge a registration fee.
Can I build a suite above my garage instead?
Often yes, within the height limits for backyard buildings. The existing walls and footings must carry a second floor, which usually needs a structural review and may need new footings. The upside is you keep your parking.