Using a drill to attach pressure treated wood deck boards.
Leave a gap between pressure treated deck boards when the wood is wet.

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.

Further Information

VIDEO TRANSCRIPT
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.

12 COMMENTS

  1. Our deck was recently constructed with regular pressure treated wood that is still wet. The builder did not leave gaps in the wood and we now find ourselves with water pooling on the deck after it rains. Should we expect this to resolve with time or is this an indication that the builder did not take the proper pitch into account when constructing the deck?

  2. Decks should be level unlike a concrete patio for example . Concrete patios need pitch to let the water drain . Decks need proper spacing at about 1/8 ” for water drainage . As your ACQ ( pressure treated ) lumber starts to dry it will shrink and the pooling of water that you’re experiencing will drain through the spaces that will form over time . If the wood was dry during installation however , the builder made an error when butting them tightly . I would contact the builder , but chances are that the wood was wet during time of installation so your deck will probably be fine over time .

  3. Have a wooden deck. (20+years old}. To utilize the space below, had a shed build for outdoor equipment etc. Have continual problems with water draining into the shed. Not a super big problem but irritating. I’ve caulked the shed roof multiple times and other “resolution.” Should add that I have a canvas roof placed above the deck from spring through Sept/Oct. (No problems with water getting into the shed then). The late fall/winter months are a problem. Wondering if there is a product to place between the deck boards to close these gaps? Also wondering about products to place on top of the deck boards that are waterproof for the shed below.

  4. We have wood deck off the ground made mistake in painting it and don’t want to strip or sand it. Can you put marine board over top of original

    • Hi, Brenda!
      We would need more information, please. Are you saying you want to completely cover the deck with marine board? And how did you plan to install it?
      Also, is the deck flat, or are there railings or stairs in addition to the platform?
      Thanks for your question.

  5. I installed my pressure treated boards slightly touching. When it’s dry there’re about perfect width cracks between them but after a rain they swell until they are water tight for several days. In the winter they stay closed up about all the time. Any ideas?

  6. Yeah, that’s bollocks. When it rains, you want a gap. When it rains, the deck boards swell. If you’ve butted them up, there will be no gap when it rains. When it rains, the boards will not drain. In the winter, they will be tight and touch and rot.

  7. Our deck contractor placed the pressure treated deck boards too close and now we have issues with debris accumulating in the gaps which restricts water drainage. Is there a tool we could use to make the gap between the boards wider?

  8. i’ve built several decks. i’m in houston – so you know the texas weather is very hot. all of my deck boards were pretty much damp when i got them. i butted them up together and a week later – 1/4″ gap happened naturally, so i have the complete opposite situation. and hey don’t swell in the rain- they simply drain. i’ve had several homes in houston and done this quite a few times w/ exactly the same results. just thought i would share

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