Why don’t deck builders gap pressure treated decking?

When installing pressure treated decking boards, install them tight to each other.

Why?

Pressure treated lumber shrinks as it dries.

After the wood dries out, the resulting gap between decking boards will be too big.

[crhcarpentry]

As primarily a deck builder, always gap your boards. Those boards will not shrink enough to make that big of a difference. A 1/2” gap would still be fine. Just means your lumber will last longer.

You nail that catspaw into every joist like that, water will get in the holes you create with that catspaw, and it’ll rot.

Don’t give bad advice.

[Cardbordboxonfire]

As a Non Carpenter for the past 26 years, I can say “I didn’t know that”
Then go to the comments and see something I also didn’t know, then I realize you opened up a battle field full of carpenters, and self proclaimed carpenters. They are livid 😂
And now I don’t know what to believe

[garydail]

My Neighbors did this and, after 2 years, had to pay a fella to take every other board out and cut 1/2" off router the edge and reinstall . " looked like a lake on the deck when it rained"

[jmcguire]

So this is the guy who's decks I have to keep rebuilding.

[abacab]

As someone with 40 years experience, you can never predict how much they will shrink, and 1/8" is not enough. Even 1/4" a lot of tree debris and leaves will get caught. I leave an 1/8th inch, and end up with 1/4-3/8" but even 1/2" is fine, and is what I try to do on my own decks.

[IIIIIIPETEIIIIII]

And if the boards are partially dried out when you lay them, if you don’t leave expansion gaps, they will buckle! Also, narrow gaps trap rotting plant material which holds moisture. In icy conditions, damage may occur and despite being treated, the wood is more likely to rot.

Always leave 3-5mm gap when laying decking like this!!

[paulmryglod]

Ive done it both ways, and thankfully the customers were happy with the results. I think a larger gap up north is a better idea for leaves, snow, etc.

[arcadiagreen]

I can confirm this. I recently built my uncles deck this way with heavy "wet" boards and butted them all together. Now that it's dried out a few weeks later it has excellent gapping

[michaelmckay]

If the gap is too small, the boards will rot from the sides as water and debris is trapped between them. The gap should be large enough that the debris will fall through or be easily cleaned out.

[mr.fahrenheit]

That's not always true. I pulled deck boards tight to begin with and the rainwater tends to pool on the surface even on seasoned decks...i switched to using a 10d nail as a spacer and it hasn't failed me since. Rather have a quarter inch gap than no gap at all.

[ahamichiana]

Use a standard 16D framing nail as a gap on fresh PT green boards.

[erichilyard]

I've been in the trades for 25+ yrs. Always gap your boards! Installing them tight will result in improper/irregular gapping and cause more moisture problems, cupping/warping.

[alm]

well you keep on building them the way you like. Myself I use a Camo tool which gaps the boards uniformly and you don't see any screws.

[bryenlink]

Installed them nice and tight last summer. This summer it’s been hot without any rain, and some of the gaps are good 1/2”. Keep ‘em tight boys and girls.

[matthewmindler]

The end grain of this board is upside down, you should always put the arch up

[thanos]

Best advice ever. I’ve built hundreds of P/T decks. Ensure what side of the board goes up first to prevent cupping and it’s much better to toe nail then face nail, but this is actually better with no gaps if the moister content of the boards are very obvious. Face nailing of a dryer board may result in squeaking once expansion & contraction occurs multiple times and some small splitting. But over all yes it is better to bring the. Boards together tight. 👍

[davesuniverse]

Actually your gap size should take a couple of things into account. First is debris buildup from things like surrounding tree leaf & seed litter. So many forget to account for this simple, yet, most important aspect to keep from creating debris buildup which creates moisture issues & eventually contributes to rot. I also totally agree with the comments on using a cats claw or other tools that might tear up or score the wood surface in manner contributing to rot. Smooth wood vs. rough surfaces shed water more readily. With that said, if your gaps are not large enough debris can actually get easily stuck becoming wedged & at times extremely difficult to remove, contributing to moisture buildup & rot. Things like leaf & seed stems are notoriously problematic, even with blowers, brooms, & pressure washers…
Second is to account for zoning & whether there are impervious surface considerations. Gap sizing is sometimes taken into account in allowances to drop square footage impervious calculations on a site, with gaps large enough sometimes allowing for lowered square footage for impervious surface totals & thus allowing you to develop more area for construction if needed. This is, however, totally dependent on local codes & their interpretation.

[tomthumb]

Don't forget to turn the crown in the grain of the wood up . Years down the road it will cup up & hold water .

[amclaughlin]

Wouldn't they swell again when wet and make it so there is no gap

[BrianLawrence-vkpu]

#1. Gapping does not increase decking life for any lumber. All wood, treated or not, will shrink enough in 12 weeks to allow for water shed.

#2. You are correct about punturing joists. There is a joist pry tool made to utilize physics that straightens decking without damaging joists. It costs about $100 and requires only seconds to use.

#3. The most important step almost every installer ingnores is the most important. It is crowning the cup. Nearly all boards have a natural cup when examined by cut-end. This is due to wood growth in relation to rings and becomes more exaggerated as the wood dries. Almost every contractor orients decking with the wrong test. The aesthetic quality of deck boards should be secondary to cup orientation.