What are the Ontario Building Code requirements for a raised deck?

The Ontario Building Code sets specific structural and safety requirements for raised decks, and Ottawa's climate adds practical considerations that go beyond the minimum code standards. Any deck attached to a dwelling that stands more than 600 mm above adjacent grade requires a building permit from the City of Ottawa and must comply with OBC Part 9 for residential construction.

Foundation requirements are where Ottawa's conditions have the most impact. The OBC requires frost-protected footings, which in Ottawa means a minimum depth of 1.2 metres below finished grade to get below the frost line. Most Ottawa contractors go to 1.5 metres for additional insurance against frost heave, particularly in clay-heavy soils common across Kanata, Barrhaven, and the east end. Footing diameter depends on the tributary load area but typically ranges from 200 mm to 350 mm diameter sonotubes for residential decks. The base must bear on undisturbed native soil or properly compacted engineered fill.

Structural framing requirements under the OBC specify minimum lumber grades, joist sizes, and spans. For a standard residential deck, pressure-treated SPF lumber rated No. 2 or better is the baseline. Joist spans are governed by species, grade, size, and spacing. A common configuration uses 2x10 joists at 16-inch centres, which provides spans up to approximately 3.6 metres depending on the specific lumber grade. Beams must be engineered for the loads they carry, and the OBC's span tables provide the sizing requirements based on post spacing and tributary width.

The ledger board connection to the house is one of the most scrutinized elements during inspection. The OBC requires a positive mechanical connection, typically using lag screws or through-bolts at specified intervals into the house's rim joist. Flashing above the ledger board to prevent water infiltration behind the house's cladding is mandatory. Ottawa inspectors pay close attention to this detail because moisture trapped behind a ledger board leads to structural rot that can compromise both the deck and the house.

Guard rails are required on any deck surface more than 600 mm above grade. The OBC mandates a minimum guard height of 1,070 mm, with openings that won't allow passage of a 100 mm sphere. This prevents children from slipping through gaps. Stair guards follow the same 1,070 mm height requirement, and stair treads must maintain uniform rise and run throughout the flight, with a maximum rise of 200 mm and minimum run of 235 mm.

Ottawa's substantial snow loads, rated at approximately 2.4 kPa for ground snow, mean your deck's structural design needs to account for winter accumulation even if you plan to shovel regularly. The OBC requires designing for the full snow load regardless of maintenance intentions. Combined with Ottawa's fifty-plus annual freeze-thaw cycles that stress fasteners and connections, using code-minimum materials and hardware isn't always the wisest approach.

For guidance on how these code requirements apply to your specific deck plans, the Patio IQ resource covers Ottawa-specific building considerations in detail.

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