✓ The Decision
- Assume you need a permit if the deck attaches to the house, sits more than ~600 mm (24″) above grade, has stairs or guards, or is over your municipality's size threshold. Most real decks tick at least one box.
- Attach with a ledger only if you'll do it exactly right — bolted through to the house rim joist, properly flashed, with lateral-load connectors. A bad ledger is the single most common cause of deck collapse.
- Go free-standing if you'd rather not cut into the house envelope — the deck carries itself on its own posts and beams, sidestepping the ledger and flashing entirely. It costs a bit more in framing and footings.
- Build to the guard and stair numbers from day one — guard height, the 100 mm gap, and stair rise/run are the items inspectors measure, and retrofitting them is miserable.
A deck is the project homeowners most often build without realizing it's inspected structure. The three things that decide whether it passes — and whether it's safe — are the permit, the connection to the house, and the guards and stairs. None of them are hard; all of them are measured. This guide walks the numbers and the one detail that quietly fails decks years later.
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Does Your Deck Need a Permit?
Across most of Canada, a deck needs a building permit once it's a real structure rather than a low platform on the ground. The common triggers:
- Height. A walking surface more than about 600 mm (24″) above grade almost always needs a permit — and that same height triggers a required guard.
- Attachment. Attaching to the house (a ledger) brings the connection and the house's structure into the inspection, and usually means a permit even for a lower deck.
- Size. Many municipalities exempt small, low, free-standing platforms (thresholds vary, commonly framed in the 10–15 m² / shed-sized range) but the exemption evaporates with height, stairs, or attachment.
- Stairs and guards. Once you add stairs or a required guard, you're into inspected territory regardless.
Zoning still applies even when no building permit does — setbacks and lot coverage don't care about exemptions. For the broad picture see Permits & Property Lines, and for the document package a permit application needs, see What Your Permit Application Actually Requires. Because deck thresholds are so local, the most valuable first step is confirming your municipality's exact trigger and required drawings up front — a quick feasibility check before you design saves the redraw.
The Ledger vs Going Free-Standing
How the deck meets the house is where safety is won or lost. You have two legitimate routes, and the right one depends on how confident you are in the detail.
Attached — the ledger, done right
A ledger transfers a big share of the deck's load into the house wall, so it has to be done to the letter:
- Fasten into the rim/band joist, never the sheathing or studs alone. Through-bolts or proper structural lag screws into solid framing — not nails, and not deck screws.
- Flash it. Flashing tucked behind the cladding and over the top of the ledger keeps water out of the wall. Rot behind an un-flashed ledger is exactly how "solid" decks let go years later.
- Add lateral-load connectors. Bolts resist the deck pulling down; lateral connectors resist it pulling away from the house. Modern practice (and many jurisdictions) expect them on attached decks.
Free-standing — no ledger at all
A free-standing deck carries its full load on its own posts, beams, and footings, with no connection to the house (or just a gap-spanning landing). It avoids the ledger and the flashing failure point entirely, which is why many builders prefer it on tricky walls (over masonry, brick veneer, or insulated cladding) or where the homeowner wants the house envelope left intact. The trade-off is more framing: typically an extra beam and an extra row of footings near the house. Our deck foundations & frost guide covers footing depth, and the foundation calculator prices the extra row.
Neither route is "the" right answer — a correctly built ledger and a correctly built free-standing deck are both code-compliant and safe. The wrong answer is a half-measure: a ledger nailed on without flashing or lateral connectors.
Guards & Railings: The Numbers Inspectors Check
| Requirement | Common Canadian figure |
|---|---|
| Guard required when surface is above… | 600 mm (24″) above grade |
| Guard height, deck ≤ 1.8 m above grade | ≥ 900 mm (35½″) |
| Guard height, deck > 1.8 m above grade | ≥ 1070 mm (42″) |
| Maximum opening (baluster gap, bottom rail) | < 100 mm (≈ 4″) — no 100 mm sphere passes |
| Climbability / "ladder effect" | Restricted in some provinces (e.g., Ontario) — confirm locally |
The 100 mm rule applies to every opening — between balusters, under the bottom rail, and beside the stairs — and it's the one inspectors check with an actual gauge. A few provinces also restrict horizontal members that form a "ladder" a child could climb; whether that applies depends on which code edition your province has adopted, so confirm before you choose a horizontal or cable design.
Stairs
Exterior deck stairs have their own dimensional rules, and consistency matters as much as the numbers — a single odd step is a trip hazard and a failed inspection:
- Rise: about 125–200 mm (5–7⅞″) per step.
- Run / tread: roughly 210–355 mm (8¼–14″), with treads commonly ≥ 235 mm (9¼″).
- Uniformity: risers and treads within about 5 mm of each other across the flight — inspectors measure the variation.
- Handrail: required on stairs with more than three risers, set about 865–1070 mm (34–42″) above the tread nosings, and graspable.
- Guard on stairs: required where the drop beside the stair exceeds 600 mm, to the same opening limits as the deck guard.
What Inspectors Actually Flag
From the field, the failures are predictable — build to this short list and most inspections are uneventful:
- Guard too low or gaps too wide. The 900/1070 mm heights and the 100 mm opening are measured every time. Composite and cable systems get extra scrutiny on the gap.
- Inconsistent stairs. A rise or run that drifts more than ~5 mm across the flight, or a missing/low handrail.
- Footings above frost. Footings that don't reach the local frost depth heave — see the frost guide. This is a structural fail, not a cosmetic one.
- Ledger problems. No flashing, nailed-on attachment, or missing lateral-load connectors — the trifecta behind most ledger failures.
- Undersized or over-spanned framing. Joists or beams spanning further than the span tables allow for their size and spacing.
✗ Deal-Breakers — Don't Build Past These
- A ledger you can't flash or bolt properly. Over brick veneer, foam-insulated cladding, or a wall you can't reach the rim joist through — go free-standing instead of forcing a compromised ledger.
- Skipping the permit on a raised or attached deck. Unpermitted decks surface at resale and in insurance claims, and a guard or ledger failure on one is a liability you don't want to own.
- Designing the guard or stairs by eye. "Looks about right" fails the gauge. Set the heights, gaps, and rise/run to the numbers before you cut.
- Footings that don't reach frost depth. No railing detail matters if the whole deck heaves and racks every spring.
The Safest Path Forward
- Call the building department with your deck's height, size, and whether it attaches — get the permit answer and the exact local numbers for your address.
- Choose your connection — a properly flashed, bolted, laterally-tied ledger, or a free-standing frame that avoids it.
- Get the footings below frost first (price them here); everything else rides on them.
- Build guards and stairs to the numbers — 900/1070 mm guards, <100 mm gaps, consistent 125–200 mm risers, a graspable handrail.
- Book inspections at the stages your permit lists and keep the paperwork — it's a resale asset.
Bottom Line
Most Canadian decks need a permit the moment they rise above ~600 mm, attach to the house, or get stairs. Win the build at the connection — a ledger done exactly right, or a free-standing frame that skips it — and pass inspection by building guards and stairs to the measured numbers. Price the structure with the Deck Cost Calculator and the footings with the Deck Foundation Cost Calculator, then confirm your local thresholds before the first cut.
Frequently Asked Questions
Do I need a permit to build a deck in Canada?
Usually yes once the deck is more than about 600 mm (24″) above grade, attaches to the house, or has stairs and guards. Small, low, free-standing platforms are often exempt (thresholds vary by municipality), but zoning setbacks always apply. Confirm with your local building department.
How high does a deck railing have to be?
In most of Canada, a guard must be at least 900 mm (35½″) where the deck is up to 1.8 m above grade, and at least 1070 mm (42″) where it's higher. Openings must be small enough that a 100 mm (about 4″) sphere can't pass. Some provinces also restrict climbable horizontal members — confirm locally.
Is a free-standing deck better than attaching to the house?
Both are code-compliant when built correctly. A free-standing deck avoids the ledger and flashing — the most common deck-failure point — at the cost of an extra beam and row of footings. An attached deck saves that framing but must be bolted into the rim joist, flashed, and fitted with lateral-load connectors. Neither is wrong; a poorly attached ledger is.
What are the deck stair code dimensions?
Exterior stairs typically run about 125–200 mm (5–7⅞″) rise and 210–355 mm (8¼–14″) run, with risers and treads consistent within roughly 5 mm across the flight. A graspable handrail is required on stairs with more than three risers, set about 865–1070 mm above the nosings. Confirm exact figures with your municipality.