each decking species will have different movement properties, but let’s use ipe as an example. if we install a typical 1×6 ipe decking board today using our weather conditions of 90% humidity and 96° while assuming the wood is 5.5″ wide, it will maintain that width through the heat and humidity; however, as we d into the fall season, both the heat and humidity begin to drop.
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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.
the sweet spot – most people agree that 3/16” is a good gap between boards. going more than a ¼” may get a little too wide. the width of a nail head is just about right. treated lumber – usually treated lumber will have some shrinkage so you can butt the boards almost right against each other during installation.
proper deck board spacing should have a 1/8-inch gap after the decking has dried out. if you install your decking using wet boards, pressure-treated decking that has not yet dried out, then you should install them with no gap as a gap will be created as they dry and shrink. deck spacing isn’t anything to take lightly.
how much room should you leave between treated lumber boards? if you’re building with kiln-dried lumber, make sure to leave boards ⅛’’ apart for the best results. you can use a framing nail or a 16d nail to make sure that each board is a uniform distance from each other.
this article explains proper gap size to leave between deck boards for drainage and drying, and extra steps to take to protect deck joists from rot. we include a description of tightly-butted tongue-and-groove pressure treated deck boards as well as typical 5/4" thick pressure treated deck boards that should be spaced for drainage.
adjust the spacing between deck boards gradually over the next 10 rows of decking until the distance to the house is equal. the last board won’t look good if it’s skinny or cut at an angle. in most cases, it’s best to start with a full board on the outside edge of the deck and work toward the house so the odd board is less visible.