Floating deck rules under the Ontario Building Code?

The 2024 Ontario Building Code includes a specific exemption for floating decks under section 9.12.2.2(7). It lets a deck sit on shallow or surface-level foundations, skipping the frost-depth rules that normally apply, but only when five conditions are all met at the same time.

The five conditions for the floating-deck exemption

• Not more than one storey
• Not more than 55 square metres in area
• The distance from finished ground to the underside of the joists is not more than 600 mm (24 in.)
• The deck does not support a roof
• The deck is not attached to another structure, unless it can be demonstrated that differential movement will not adversely affect the performance of that structure

Every one of those must hold. If your deck is attached to the house, the fifth condition is the one to read closely: an attached deck qualifies only if it can be demonstrated that differential movement will not adversely affect the performance of the house. Ask your builder or designer how they would show that, or whether the drawings use the table depths instead.

The exemption for post anchoring works the same way. Section 9.23.6.2 of the 2024 Ontario Building Code says posts on low decks must be anchored against uplift and lateral movement, but that requirement does not apply where the platform meets the same five conditions above.

A few things the exemption does not change. Zoning still applies: both Zoning By-law 2008-250 and Zoning By-law 2026-50 are in effect for Ottawa, and the most restrictive provisions of both apply to your lot. The 2024 Ontario Building Code's guard rules still apply: if any side of the deck has a drop of more than 600 mm within 1.2 m of the edge, a guard at least 900 mm high is required for a deck serving one dwelling unit at or below 1 800 mm above finished ground. Stair rise and run limits still apply. And the permit rules still apply: a deck attached to the house with a walking surface more than 600 mm above grade needs a permit regardless of size, and so does any deck that is the principal access to the building.

On soil, the floating exemption removes the frost-depth requirement, but it does not remove the need to think about what is under those footings. Where the ground is filled, peaty or contains sensitive clay such as Leda clay, section 9.15.1.1 of the 2024 Ontario Building Code directs the footing design to Section 4.2, which means an engineered design. A builder or engineer can tell you whether that applies to your lot.

Before any footing holes are dug, even shallow ones for a floating deck, a locate request through Ontario One Call is required by the Ontario Underground Infrastructure Notification System Act, 2012: submit it at least five business days before you plan to dig, and it is free.

If your deck will sit at or below 600 mm above grade and is freestanding, your next step is confirming the zoning setbacks with the City and checking whether your soil conditions are straightforward enough for the floating exemption to work cleanly.