Treated Wood on Decks: What the Updated 2024 IRC Now Required

Treated Wood on Decks: What the Updated Building Codes Now Require

If you're framing a deck with pressure-treated lumber, the 2024 IRC has specific things to say about what's acceptable - and where. The rules around decay-resistant and pressure-treated wood tightened up in this edition, and getting it wrong isn't just a failed inspection. It's rot, structural failure, and a warranty void in one package.

The Core Issue: Not All Treated Wood Is the Same

Pressure-treated lumber is graded by retention level - how much preservative is driven into the wood - and the 2024 IRC is more prescriptive about which retention level is required for which application. Ground-contact framing, posts embedded in concrete, and members closer than 6 inches to grade now require higher retention levels than above-ground framing. Using the wrong grade in the wrong place won't be visible at install, but it will be obvious in a few years.

Naturally Durable Wood Has New Rules Too

The 2024 IRC also updated its language around naturally decay-resistant species like redwood and cedar. These are still permitted for above-ground applications, but the code now distinguishes more clearly between heartwood and sapwood - only the heartwood of naturally durable species counts as decay resistant. If your supplier is selling mixed-grain cedar as a decay-resistant option, that's worth a closer look before it goes into the ground.

Hardware Compatibility Matters More Than Ever

Tighter treated wood standards also have implications for fasteners and connectors. The preservatives used in modern pressure-treated lumber are corrosive to standard steel hardware. The 2024 IRC reinforces requirements for hot-dipped galvanized, stainless steel, or specifically rated coated fasteners wherever treated lumber is used - including joist hangers, post bases, and ledger fasteners.

Worth Reading Before You Order Materials

This is a topic where the details matter and the full breakdown is worth your time before you spec anything out.

Read the full "2024 IRC Deck Code Changes: The New Rules on Treated Wood"