The Short Answer
In Ontario, a deck generally requires a building permit when it is more than 24 inches (600 mm) above grade, or when it's attached to the house in a way that affects the structure, or when it includes a roof, or when it exceeds the size thresholds in your municipality's zoning by-law.
Below that, a low, freestanding, ground-level deck may not need a permit — but "may not" is doing real work in that sentence, because the thresholds vary by municipality and by whether the deck is attached, covered, or serving an exit. Always confirm with your local building department before building.
When a Deck Definitely Needs a Permit
The reason the height threshold exists is falls. Below 24 inches, a fall is generally not life-threatening, so the code is relaxed. Above it, guard requirements, stair geometry, and structural adequacy all come into play — and those are exactly the things a permit review checks.
Zoning: The Check That Stops Decks Before Design
Even a deck that's structurally simple can fail on zoning. Before you design anything, confirm against your municipality's zoning by-law:
- Rear and side yard setbacks — a deck is a structure occupying your lot, and it must respect setbacks, though some municipalities allow reduced setbacks for unenclosed decks.
- Lot coverage — deck area usually counts toward permitted lot coverage, which matters if your house and any outbuildings already consume most of the allowance.
- Height limits — relevant for raised decks and anything with a roof.
- Privacy and screening — some municipalities regulate deck height near property lines for overlook reasons.
- Conservation authority jurisdiction — if you're near a ravine, watercourse, or regulated area, you may need approval beyond the building permit. This affects a meaningful number of properties in Caledon, Halton Hills, and parts of Toronto.
“A deck that violates a setback can be ordered removed — after you've built it. The zoning check costs an afternoon and prevents that outcome entirely.”
Where Engineering Comes In
A low ground-level deck is largely a carpentry project with prescriptive code provisions. A raised or elevated deck is a structural one, and this is where generic plans tend to fail.
A raised deck has to carry its own loads plus live loads from people and snow, and transfer them to footings that go below the frost line. In Ontario, frost depth is significant — typically around 4 feet in much of the GTA, deeper further north. A footing that doesn't reach below frost will heave seasonally, and heaving footings crack decks, twist framing, and pull ledger connections away from the house.
The specific things engineered drawings address:
- Footing size and depth calculated for the actual loads and the local frost depth.
- Beam and joist sizing for the real span and loading, including snow.
- Ledger attachment detailing — the connection between the deck and the house is the highest-risk element on most decks, and its detailing depends on your home's rim board and floor structure.
- Guard and stair design meeting current code requirements.
- Lateral load resistance — how the deck resists racking, which is frequently omitted in DIY designs.
What a Deck Permit Submission Includes
For a deck or porch that requires a permit, a typical submission includes:
- A site plan showing the deck's location, dimensions, and distance from property lines
- Construction drawings — footing locations and depths, beam and joist layout with sizes and spacing, stair and guard details
- Connection details, particularly the ledger attachment to the house
- Structural drawings sealed by a P.Eng., where the municipality requires them for raised or covered structures
- A zoning compliance summary addressing setback and lot coverage
Timing: Why Fall Is When to Plan
Deck permit applications face the same seasonal intake pattern as other permits — spring is the busiest review period, when everyone is getting ready for summer. Applying in the fall generally means faster review, and it puts you in a position to build as soon as conditions allow.
Fall is also a reasonable time to actually build, within limits. Footings require excavation and concrete, which gets difficult once the ground freezes — so if you want to pour this season, October is the practical window. Otherwise, do the drawings and permit now and build first thing in spring. Our foundation and drainage guide covers the freeze deadline in more detail, and our permit timeline breakdown gives the review ranges.
Deck and Porch Permits Across the GTA
Height thresholds, setback rules, and review practice vary by municipality. Find your city:
May Engineering Inc: Deck Drawings and Permits
May Engineering Inc prepares deck and porch permit submissions — site plans, construction drawings, footing and connection detailing, and P.Eng.-sealed structural drawings where required. We size footings to your local frost depth and detail the ledger connection to your specific house, which is what keeps the deck sound through Ontario's freeze-thaw cycles.
Building a deck, porch, or covered outdoor structure this season or next? Send us your dimensions and a photo of the area and we'll tell you what the permit requires.
Building a deck or porch?
Free initial consultation. Permit drawings and sealed structural drawings for decks across Ontario.