Guide
Ontario's 10 m² rule: when a backyard studio or bunkie needs a permit
Ontario's building rules draw a line at 10 square metres. Here is what that line means for a small backyard studio, office or bunkie, where the better-known 15 m² figure fits in, and what still applies when no building permit is needed. General information, not legal advice.
The rules
What the Building Code Act says
Ontario's Building Code Act, 1992 decides what counts as a "building". Its definition starts with "a structure occupying an area greater than ten square metres", and it also covers a structure of 10 m² or less that contains plumbing. Section 8 of the Act requires a permit to construct a building.
So a structure that occupies 10 m² (107.6 sq ft) or less, has no plumbing and isn't otherwise designated is not a "building" under the Act. It doesn't need a building permit, and the Building Code doesn't apply to it, whatever it's used for: a studio, an office or a home gym. For anything other than storage, this is the one permit-free route that works across the whole province.
The 15 m² exemption is for storage sheds
Since April 2022 the Building Code has also exempted some sheds of up to 15 m² (161.5 sq ft) from permits. The current wording is in the 2024 Ontario Building Code, Division C, Article 1.3.1.1.(6). The shed must be no more than 15 m² in gross area, one storey, not attached to a building or any other structure, and without plumbing. It must also be "used only for storage purposes ancillary to a principal building on the lot".
Read plainly, a studio, office or gym isn't a storage shed. So for those uses the 15 m² figure usually doesn't help, and the 10 m² line in the Act is the one that matters.
Some municipalities read it more broadly
Your local building department applies the Code, and departments don't all read the shed exemption the same way. Burlington's chief building official allows accessory buildings of up to 15 m² without a permit when they're used for purposes ancillary to a house. Oakville's web page and an Ottawa advisory also describe the exemption without storage-only wording.
Others read it strictly. Toronto, Brampton, Hamilton, Vaughan, Markham, Kawartha Lakes, Tiny and Dysart treat the 15 m² exemption as storage-only, so a studio, office or gym over 10 m² needs a permit there. If your municipality isn't on either list, assume the strict reading until they tell you otherwise.
Has anything changed recently?
Not for the permit limits, as far as I can find. The provincial housing changes from 2022 to 2026, including Bill 23, Bill 185 and Bill 17, changed zoning and additional-unit rules, but none of them widened the permit exemption for small accessory buildings. Garden suites are homes, and they always need a permit. Rules do change, so check the current versions before you build.
Artist's rendering of the JPD design style
Size and measuring
How the area is measured
The Act doesn't say how "occupying an area" is measured, including whether roof overhangs count. The Code's 15 m² test uses gross area, measured to the outside faces of the exterior walls, and a loft floor would add to it. Municipalities differ, and some may count overhangs toward the 10 m² line. The careful approach is to ask your building department how they measure before you build.
Where JPD designs fit
JPD designs measure about 3.66 × 2.44 m (12 × 8 ft) to the outside of the walls: about 8.9 m². They're designed to stay under Ontario's 10 m² threshold: one storey, fully detached, no plumbing and not for sleeping. The roof overhangs extend beyond the walls and aren't included in the 8.9 m² figure. Zoning still applies, and your municipality has the final word on whether a permit is needed.
What can push a small building over the line
Plumbing of any kind, even a single sink, makes a structure of any size a "building". A loft or second level adds floor area and a storey. An attached deck, porch or pergola can join everything into one larger structure. And sleeping or living in it changes the use entirely. Keep the building simple, separate and dry.
What still applies
Zoning applies at any size
A permit exemption only takes a building out of the Building Code. Your municipality's zoning bylaw still applies: where accessory buildings can go, setbacks from lot lines, height limits (often 2.5 to 4.5 m in the GTA), lot coverage, how many accessory buildings you can have, and what they can be used for. Some towns, including Oakville, Milton, Muskoka Lakes and Huntsville, don't allow an accessory building to be used for a business. Many municipalities offer a zoning check before you build; in Toronto it's the Zoning Applicable Law Certificate.
Cottage and waterfront lots
Waterfront lots add their own layer. Shoreline setbacks of 20 to 30 m from the high-water mark are common, and site plan control or a community planning permit can apply near lakes, as it does in Muskoka Lakes and Huntsville. Conservation authorities regulate floodplains, shorelines and wetlands; Ontario Regulation 41/24 exempts non-habitable accessory buildings of 15 m² or less from their permits, as long as they're not in a wetland or watercourse. Keep well clear of the septic system too: the Code asks for at least 5 m between a leaching bed and a structure.
Power, heat and plumbing
Wiring always needs a notification to the Electrical Safety Authority, with or without a building permit. Only the homeowner (in their own home) or a licensed electrical contractor can do the work. Gas appliances need a certified gas technician, and wood stoves bring permits and inspections of their own, so electric heat is the simple choice. Plumbing is the one thing to leave out entirely.
What about a bunkie?
In Ontario, "bunkie" usually means a small cabin for guests at the cottage. If people will sleep in it, it's no longer a simple accessory structure: sleeping or living space is a dwelling use, which needs a building permit and is barred by most accessory-building zoning. A bunkie-style building used by day, as a studio, reading room or office, follows the same 10 m² rules as any other small building.
Artist's rendering of the JPD design style
Before you build
A short checklist
1. Ask your building department, in writing, whether your project needs a permit and how they measure the area.
2. Check zoning: setbacks, height, coverage, the number of buildings and the permitted use.
3. On a waterfront or rural lot, check site plan rules, the conservation authority map and where your septic system is.
4. Plan any electrical work with an ESA notification.
5. Keep the answers you get with your drawings.
About this guide
This guide is general information about Ontario's rules as of October 2026. It isn't legal advice, and it's awaiting legal review. Rules and local interpretations change, and your municipality has the final word on your property. If something here looks out of date, please write to john@johnpfeifer.design.
Artist's rendering of the JPD design style
General information, not legal advice. Check with your municipality before you build. Last reviewed October 2026.
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