Ontario deck rules, in plain English
Every deck in Ontario has to meet the Building Code, permit or not. The rules people trip on: a guard on any side more than 600 mm above the ground, stair risers between 125 and 200 mm, footings 1.2 m deep, and a ledger bolted into the house rim joist, never into brick.
Guards (the railing)
Any open side of the deck that's more than 600 mm above the ground nearby needs a guard. That's the code's word for a railing that stops people falling.
- 900 mm high if the deck is no more than 1.8 m above the ground; 1,070 mm if it's higher (OBC 9.8.8.3).
- No opening big enough for a 100 mm ball to pass through (OBC 9.8.8.5).
- Nothing a kid can climb between 140 mm and 900 mm above the deck, which is why horizontal rails don't pass.
- A wood guard built to Supplementary Standard SB-7 is the simple route: 4×4 posts no more than 1.5 m apart, 2×4 rails, 2×2 pickets and a 2×6 cap.
- Aluminum and glass systems need the manufacturer's Canadian evaluation for the exact system.
Stairs
A 914 mm (3 ft) deck split into four steps gives 229 mm risers, which fails. Six equal risers of 152 mm pass, and that's what the app draws.
| What | Rule |
|---|---|
| Rise (each step up) | 125–200 mm, all within 5 mm of each other |
| Run (each step deep) | 255–355 mm |
| Width | At least 860 mm |
| Handrail | Needed with more than 3 risers, 865–1,070 mm above the nosings |
| Stringers | At least 235 mm deep, 90 mm left after notching, no more than 900 mm apart |
| Bottom | On a pad or patio stone, not on soil |
Footings and posts
- Footings sit on undisturbed soil at least 1.2 m below finished ground, below the frost line (OBC Table 9.12.2.2).
- Piers within 1.2 m of the house go down to the house footing level, so the deck doesn't heave against the foundation.
- Each pier is sized for its load (1.9 kPa live plus 0.5 kPa dead) at 75 kPa soil bearing.
- Posts are at least 6×6 and sit on a galvanized base anchored into the concrete.
- Deck blocks are only allowed for a small, low, freestanding, uncovered deck: up to 55 m² with joists no more than 600 mm above the ground.
Joists, beams and the ledger
- Joist and beam spans come from the 2024 code table (9.23.4.2) or your City's deck table, whichever is shorter.
- Joists can overhang the beam by up to 600 mm; beams overhang their end post by at most 305 mm.
- Rows of blocking go no more than 2,083 mm (6 ft 10 in) apart.
- An attached deck's ledger is bolted to the house rim joist with ½ in galvanized lags, staggered, no more than 406 mm (16 in) apart.
- Never fasten a ledger to brick or stone veneer. The deck stands on its own posts there instead.
- A freestanding deck with posts taller than 600 mm needs knee braces so it can't rack sideways.
Decking and materials
- Wood decking is at least 25 mm thick on joists no more than 406 mm (16 in) apart.
- Composite decking needs its Canadian evaluation (it'll say the span it's rated for).
- Framing is pressure-treated, and every nail, screw, bolt and hanger is hot-dip galvanized or stainless.
When it stops being a simple deck
A roof, a pergola, a privacy screen or a hot tub adds loads the standard deck isn't built for. Those need an engineered design, and DivineDesigner flags them instead of pretending.
Questions people ask
How high does a deck railing need to be in Ontario?
900 mm if the deck is no more than 1.8 m above the ground, 1,070 mm if it's higher. A guard is required on any side more than 600 mm above the ground.
How deep do deck footings need to be in Ontario?
At least 1.2 m below finished ground, on undisturbed soil, so frost can't lift them.
Are horizontal deck railings allowed in Ontario?
Not on a required guard. Horizontal rails are climbable, and the code doesn't allow anything that helps a child climb between 140 mm and 900 mm above the deck.
Can I use deck blocks in Ontario?
Only for a small, low, freestanding, uncovered deck: up to 55 m² with joists no more than 600 mm above the ground.
What stair rise is allowed for a deck?
Each riser is 125–200 mm, and all risers are within 5 mm of each other. Runs are 255–355 mm.
Sources
- Ontario Building Code, O. Reg. 163/24 (e-Laws)
- Ontario Supplementary Standard SB-7 (guards for houses)
- City of Kitchener: When you need a building permit
Checked 2026-10-06. Your City’s plans examiner has the final word. How we verify rules