Whether to leave a gap between pressure treated wood deck boards depends on how dry the wood you’re using is.
- Leave Gap: If the pressure treated wood has been kiln dried after treatment (KDAT), leave a 1/8” gap (the thickness of an 8-penny nail) between the boards when attaching, since the wood will expand slightly over time.
- No Gap: If the pressure treated wood hasn’t been dried and is still wet with preservative, butt the deck boards together when attaching, since the wood will shrink some when it dries.
Watch this video to find out more.
- How to Build a Wood Deck (video)
- How to Install Wood Deck Boards (video)
- How Long to Wait Before Staining a New Wood Deck (video)
- Replacing a Wood Deck with Composite Decking (video)
Danny Lipford: When people are building pressure treated decks, they often ask whether they should space the boards apart or butt them tightly together. The answer really depends on the type of wood you’re using.
Regular pressure treated wood tends to be somewhat wet when it’s new. That means, as it weathers in the sun and the heat, it will dry out some and shrink slightly.
For this reason, I usually butt deck boards as tightly together as possible, so that they’ll leave a slight gap when they do shrink.
If the wood has been kiln dried after treatment, also called KDAT, most of the moisture has already been removed in a controlled environment, so very little shrinkage will occur after installation.
In this case, some space between the boards is a good idea because the wood can actually expand slightly over time. The folks at YellaWood, recommend using an eight penny nail between rows to create adequate consistent spacing.