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pressure treated wood shrinkage

I'm building a raised patio deck using pressure treated 2x6x16 ACQ treated wood. I need to have a gap between adjoining wood planks. I don't want any more gap than is necessary for the rain to run off. The wood I'm using is quite wet. Salesman at home center wasn't sure of the amount of shrinkage.

Should I just butt them next to each other and count on shrinkage to give me a gap for rain runoff or should I use a nail for gapping them? I live in the Missouri Ozarks where we get plenty of rain.

Thanks for any advice.

Re: pressure treated wood shrinkage

Two years ago, I observed new homes being built next door. Occasionally I stop by to have a chat and advice. [real nice construction workers]
When they built the deck, they don't leave any gap between planks. Now there are approx 3/16" gap between planks.

I would say the pressure treated wood do shrink when dry.

Re: pressure treated wood shrinkage

Dennis1946 .... Typically the treated lumber purchased for consumer use is high in moisture ... >19% and is considered green .... not the treating but the moisture content is high.

Personally I recommend to use a nail space when laying the new decking. This does 2 things ... allows water drainage .... allows expansion of the decking .
The lumber will eventually dry somewhat and will shrink .... how much depends on how wet the lumber is new and how much it has a chance to dry.

Hope this helps. :)

Re: pressure treated wood shrinkage

I strongly suggest you to not use nail ...

If the wood is wet... Just put each wood plate one after each other without any space in between ...

When the plates will dried up, they will give you something like 1/8 of space between each one... Wich is good...

Re: pressure treated wood shrinkage

i say do what canuk says. that's the proper way to put down decking, pressure treated wood or not. besides, if the pressure treated wood shrinks, wouldn't it pull the planks together instead of apart? the last thing you want it to have some of the planks with gaps and some without.

Re: pressure treated wood shrinkage

I installed just delivered wet PT that were 5/4 by 6 by 16 footers that were extremely heavy about five weeks ago.
Took couple of weeks off, then built few sets of stairs, and now the railings are next. (It's summer, so family/R&R/vacation/etc. plays a hand here.)

And just today, while helping our toddler "build" an imense Thomas rail road tracks on the deck, I noticed my meticulously spaced 1/8" spaces are now at least 1/4" in most places, some as much as 3/8"!
As a matter of fact, after we moved on to do a giant floor puzzle on the middle of the deck afterwards, one of the puzzle piece actually fell into the dark "not even a crawl" space beneath while being gathered to put back in the box. These are LARGE pieces, mind you, measuring around 6 X 10 inches each.

Well, the good news is, since the gap is so wide, I'll be able to stick down a long metal skewer and push it out to the edge to retrieve it.

But, since I haven't installed the railing, yet, and will have several boards in excess even after figuring for top of the railing, I am actually going to unscrew all the boards, except the first board which is agenst the brick, and re-install each board using longer, 3" inch screws... and skinnier nail for "gap" guide tomorrow morning, and will retrieve the puzzle piece when I get to the middle deck board sometime tomorrow!

Re: pressure treated wood shrinkage

You guys that are buying "wet" pressure treated lumber must be getting it at one of the two 'large' national home centers and in addition to it being "wet' I would also bet that there are a fair number of knots and other defects in it as well - For comparison my local lumber yard sells kiln-dried, pressure-treated clear pine (no knots) for only 30-cents more than either the Lowes or Home Depot... plus, they deliver for free!

Re: pressure treated wood shrinkage

By far, you'll always get your bang for your buck at a local lumber yard, like the above poster said. Yes it does cost a little bit more, but the quality decking you can buy is worth the investment. That can be said for most all material bought outside the big box stores..

Re: pressure treated wood shrinkage

DO NOT add spacing to pressure treated deck boards. I recently built my deck and used a pry bar to draw any warped boards in as tight as i could to the board just screwed down. Within 2 weeks I had uniform gaps of 1/8" between every board which is exactly what I wanted…DO NOT SPACE THEM, THEY DO SHRINK.

Re: pressure treated wood shrinkage

I vote for using a nail as a spacer. Good thing you got a consensus.:rolleyes:
I guess it might depend on the quality of wood used.

Re: pressure treated wood shrinkage

Such an old posting.

In most cases, the planks will have tiny gaps between them when they are new.


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