An Ottawa homeowner in Barrhaven bought a 10 x 12 foot shed kit at the big-box store last spring. Sticker on the box said "no permit required." They poured a slab, set the shed on it, and called it a weekend.
Three months later, a neighbour reported it to the City. The shed was 11.15 sq m (120 sq ft), set 0.4 m from the property line, and partially covered the rear-yard easement for the storm sewer. The bylaw officer issued an order: apply for permit, demonstrate compliance, or relocate.
The "no permit required" claim on the shed kit packaging is technically true for some sheds and entirely wrong for others. Here is exactly when you need a permit for an accessory structure in Ottawa, and why some homeowners pull the permit even when they do not have to.
The 10 Square Metre Threshold
The City of Ottawa, following the OBC, requires a building permit for any detached accessory structure with a footprint greater than 10 square metres (108 sq ft). The exact wording matters:
- The 10 sqm is the building area, measured at the largest exterior dimension
- It includes overhangs greater than 600 mm beyond the wall
- It includes any covered porch attached to the shed
So a "10 x 12" shed advertised as 120 sq ft is actually about 11.15 sq m and triggers a permit. A 10 x 10 shed at exactly 9.29 sq m falls under the threshold. The popular 8 x 10 (7.43 sq m) and 10 x 10 (9.29 sq m) sizes are typically exempt; a 10 x 12 or larger is not.
The threshold applies to a single accessory structure. If you have a 9 sqm shed and want to add a second 9 sqm shed, you generally still do not need a permit for either, but the cumulative footprint counts against your zoning lot coverage.
Permit Trigger Doesn't Mean Setback Exemption
Here is the rule that catches most homeowners. The 10 sqm building permit threshold is separate from the zoning rules, which apply to every accessory structure regardless of size.
Even an exempt 8 x 10 shed has to comply with Ottawa Zoning By-law 2008-250:
- Minimum setback from the rear lot line
- Minimum setback from the side lot lines
- Maximum lot coverage when added to the principal building
- Height limit
- No encroachment on easements (for utilities, drainage, access)
Setbacks are typically 0.6 m (2 ft) from a side or rear lot line for a small accessory structure under 10 sqm in most R1 zones. Larger structures often need a 1.2 m setback. Easements override both: a shed cannot sit on a registered drainage or utility easement, regardless of zoning setback.
The bylaw officer enforces zoning even on permit-exempt sheds. Build a 9 sqm shed against the property line, no permit needed, but a complaint from the neighbour will still result in an order to relocate.
Heads up
Easements are not always visible. Many Ottawa lots have storm sewer or drainage easements running through the rear yard, registered on title decades ago and forgotten. Before you set a shed in the back corner, check the title or order a SRPR survey. A shed on an easement can be ordered removed at the homeowner's expense, even years later when the City needs to access the line.
Height Maximum: 4.5 m in R1
For accessory structures in R1 (single-detached residential) zones, the maximum height is 4.5 m (14 ft 9 in), measured to the midpoint of a sloped roof or to the parapet of a flat roof.
Most pre-fab sheds are well under this. A typical 8 x 10 ft gable shed is 2.4-2.8 m tall. The 4.5 m limit becomes relevant when:
- You want a loft or second floor in the shed (then it usually counts as a coach house, not a shed, and falls under different rules)
- The shed is on a sloped lot and the height is measured from the higher side
- You are building a "garden suite" with a steep roof for storage or living loft
Other zones (R2, R3, R4) sometimes allow taller accessory structures, especially for legal coach houses under Bill 23 framework, which can go up to 6.5 m. Always check your specific zone before designing height into the shed.
Lot Coverage: The Quiet Limit
Most R1 zones in Ottawa cap total lot coverage by buildings (principal house + accessory structures + decks above 600 mm) at 40-45% of the lot area. Some zones go to 55%; some heritage zones cap at 35%.
For a 4,000 sq ft lot at 45% coverage, total building footprint maxes at 1,800 sq ft. Subtract the house at 1,400 sq ft, you have 400 sq ft for any accessory structure. A 10 x 12 shed (120 sq ft) and a 12 x 16 deck above 24 inches (192 sq ft) eats most of it.
Lot coverage is the limit that often surprises homeowners adding a second accessory structure. The first 100 sq ft shed is fine; the second one pushes the lot over its coverage cap and gets refused.
Why Pull a Permit on a Sub-Threshold Shed
You do not have to permit a 9 sqm shed. There are still three real reasons we sometimes recommend it:
Insurance
If a shed contains a lawnmower, gasoline storage, lithium batteries, or anything else that could start a fire, your home insurance treats it as an outbuilding. Outbuildings on the policy are usually covered, but the insurer can ask about construction quality, footings, and electrical at claim time. A permitted shed with documented inspections satisfies the question instantly.
Resale
Your buyer's lawyer will ask about every structure on the lot during the title search. An undocumented shed near a lot line, or one that might encroach on an easement, is a closing-day flag that can re-price the deal. A permitted shed clears the question.
Adding Electrical or Heat Later
If you decide to run electrical to the shed, a permit becomes mandatory regardless of size, and ESA gets involved. Same with running natural gas, water, or any heat source. Pulling the permit at construction lets you wire the shed properly the first time, with code-compliant conduit, breakers, and an ESA inspection. Retrofitting it later is more expensive and requires opening walls.
What's in the Permit Package
For a shed over 10 sqm, the City of Ottawa permit application requires:
- Site plan showing lot, principal building, proposed shed, all setbacks dimensioned
- Floor plan of the shed with overall dimensions
- Elevation drawings showing height, roof slope, door and window locations
- Foundation detail (slab, footings, or post-and-beam)
- Wall section showing framing, sheathing, and roofing
- Application form with project value
For a simple kit shed, you can usually use the manufacturer's drawings as the base, marked up with your specific site setbacks and any modifications. Drawing prep cost depends on whether a designer marks them up for you or you draft them yourself for a simple project.
The City's building permit application minimum is $117, with the shed permit fee scaled to the project above that floor.
Footings: The 1.2 m Frost Rule (Sometimes)
Sheds sit on one of three footing types:
- Skid foundation. Pressure-treated 4x4 or 6x6 runners on gravel. Allowed for small sheds in non-permitted size; not always allowed for larger sheds.
- Concrete slab. Slab-on-grade, 100 mm thick, on compacted granular base. Common for permitted sheds, but slab edges can heave with frost on poor soil.
- Pier footings. Concrete sonotube footings, 1.2 m deep below grade, with post saddles. Best for sloped lots and required for sheds with significant load (heavy equipment storage, second floor).
For a permitted shed, the inspector will look at the footing detail. Skids are not always accepted for permitted sheds; pier or slab is usually required.
"The smallest legal building you build is still a building. Insurance, easements, and resale don't care that it was a kit from Costco."
Decision Tree: Do You Need a Permit?
- Is the building footprint over 10 sqm (108 sq ft)? If yes, you need a permit. Stop.
- Will it have any electrical, plumbing, or fixed heat? If yes, you need a permit regardless of size.
- Does the lot have known easements in the proposed location? Check title; if yes, the shed may not be allowed at all.
- Will the shed plus all other structures exceed your lot coverage cap? Check your zoning by-law; if yes, you need to either reduce the shed or apply for a minor variance.
- Is the shed taller than 4.5 m or located within 0.6 m of any lot line? If yes, even a small shed may need approval.
If you answer "no" to all five, you can build without a permit. If you answer "yes" to any one, the permit is required.
For a feasibility check on your shed, including a same-day easement and zoning review, call 613-862-4555 for our free 48-hour assessment. Or read about the Ottawa permit process for the bigger picture on every City filing.