What is the exact rule?
The City: Where accessory to a detached house, semi-detached house or row house, a Building Permit is not required for the construction or demolition of a detached accessory structure (garage, carport, gazebo) provided it is not more than 15 square metres, is not more than one storey and does not have plumbing.
(City of Hamilton, Building Permit, read November 5, 2026) For any other use the limit is 10 m².
| The building | Permit? |
|---|---|
| 15 m² or less, one storey, no plumbing | No |
| Over 15 m² | Yes |
| Any size with plumbing | Yes |
| More than one storey | Yes |
| Demolishing one of 15 m² or less | No |
| Turning it into a home (a detached ADU) | Yes: it becomes an additional dwelling unit |
A typical one car detached garage is well over 15 m², so it needs a permit.
What may an accessory building be used for?
Storage and uses that go with the house. The City says it cannot be used for commercial purposes or for habitation
, and its examples include garden sheds, gazebos, garages, pergolas, greenhouses, and shipping containers
(City of Hamilton, Accessory Building, read November 5, 2026). Living space in the yard is a detached ADU, a different permit with its own rules: see basement unit or garden suite.
What else applies with or without a permit?
The zoning by-law, for its size, height and distance from the lot lines. And with a permit, a professional grading plan is required for a residential accessory building unless it falls under the City's exemptions, which lot grading plans sets out. The site plan also shows any septic system on the lot (City of Hamilton, Accessory Building, read November 5, 2026).
What does the permit cost?
$6.58 a square metre for a garage or storage shed, $291 at the least (City of Hamilton, Building Permit Fees, read November 5, 2026). A 40 m² garage comes to $263 by the formula, so the $291 minimum applies; try other sizes in the permit fee calculator.
How does JDT build a garage?
Framed and roofed on its own slab, drawn on your lot first and priced in one written proposal; the garages page has more. A deck beside it follows other rules: does my deck need a permit? Under JDT Construction Inc.'s agreement the homeowner applies for the permit and pays the City's fees; who applies for a building permit explains how that works.