Treated wood in ground contact on an Ottawa deck?

For posts and components that go into the ground, the 2024 Ontario Building Code says to use preservative-treated wood or the dark heartwood of a naturally durable species. That is the Code's own wording, and it applies to any deck post or structural member in ground contact.

Health Canada identifies the two treatments available for residential construction today as Alkaline Copper Quaternary (ACQ) and Copper Azole (CA-B). Chromated Copper Arsenate (CCA) is no longer available for residential projects. If your property has an older deck built before 2004, Health Canada says it is likely to have been made from CCA-treated lumber.

When you are working with ACQ or CA-B lumber, Health Canada recommends wearing a dust mask, eye protection, gloves and long sleeves when sawing or sanding, and says never to burn treated wood indoors or outdoors.

A few things shape how this applies to your specific deck. Whether a post sits in direct ground contact or on a concrete footing above grade changes what the Code requires of it. Where the soil is filled ground, peat or sensitive clay, including Leda clay, the 2024 Ontario Building Code requires an engineered foundation design under Section 4.2 rather than the standard prescriptive footing rules. A builder or engineer can tell you whether that applies to your lot. Before any digging starts, Ontario law requires a locate request through Ontario One Call at least five business days in advance; the request is free, and it covers both public utilities and any private lines you arrange to have marked yourself.

If the deck needs a permit, the City of Ottawa's permit drawings must show the footing or foundation type, size and location, and the post sizes and spacing. The City lists three inspection stages: excavation and foundations before backfill, framing at completion of structural framing and guards, and a final inspection. The homeowner or builder books each inspection 48 hours in advance.

On the finish side, the USDA Forest Products Laboratory notes that copper waterborne treatments may keep a brown colour for about two years. For above-ground decking boards, the FPL says the service lives of naturally durable and preservative-treated woods are quite comparable, and that splitting and checking, not decay, is the most common reason treated decks are replaced. Keeping water beading on the surface rather than soaking in is the best way to slow that process.

When you set two written quotes side by side for this job, look at what each one specifies for the foundation type and depth, the board species and treatment, the guard and stair details, and whether removal of an existing deck is included or priced separately.