I am building an outdoor deck with pressure treated lumber. Should the walkway lumber be spaced to allow air flow and water drainage? If so, what spacing?

Ideally you want to have enough space so that a womans high heel won't get caught but large enough for water to drain without collecting mid sized particulates.
If the PT decking is over 19% moisture content or feels very heavy for it's size it may be laden with moisture. If this is the case use a typical 16d common nail as your spacer... 1/8 ... as the deck dries it will widen the space to 3/16.
If the decking comes KD (kiln dried), has been sitting in the sun or feels light for it's size & you are installing in the summer heat, use upwards of a 1/4 inch spacer. These then will collect moisture in the cellular structure and close the gap to the 1/8 - 3/16.

http://www.altereagle.com/
http://decks-ca.com
http://kingofcrown.com

Alter Eagle Construction & Design

Simply butt the deck lumber and the normal drying process will take care of the rest.

In short, never space deck lumber at all.

We went back-and-forth about space between deck boards for a recent project. I don't recommend "zero" spacing between boards--at least in areas like mine (Colorado). With the previous decking, the thin gaps got jammed up with pine needles and other such over the years. They were not only frustrating and impossible to clean out, but there was more rot in areas where they'd built up.

I believe our deck builders did use common nails as spacers (ala Altereagle). I haven't measured exactly, but it appears to currently be about a 3/16" spacing (in synthetic decking) and are very happy with it.

Regards,
-k2 in CO

Moderator, Miscellaneous Forum

http://www.bobvila.com/BBS/Miscellaneous

It's very important not to place the decking with no spacing.

In the winter months which is the most moisture laden time of the year for most locations, the stock will expand with the content closing the spacing when it is most crucial.

Again though you need to asses the moisture content during installation.

..and k2 you are even more correct with composites, it's extremely important to refer to the manufacturers specifications when spacing that decking as the polymers used expand almost exponentially. :)
They do have a tendency to over do it sometimes though, for example butted (end to end) decking for the most part (depending on the mean temp. at installation as well) requires a 3/16 to 1/4 spacer. I rarely do that only if there is absolutely no room for expansion.

http://www.altereagle.com/
http://decks-ca.com
http://kingofcrown.com

Alter Eagle Construction & Design

i have built a few decks around my house, and have found that spacing the boards 'one nail' apart accomplishes many things. for me, i think it just plain looks better overall, 2, it really helps with drainage, and 3, ever sweep a deck that had all the boards butted up to one another? it's like sweeping a dirt floor.

also, as mentioned before, once these boards are down, they will move around when they get soaked/dry out, so better to give them some room to move around. also make sure to figure in a little pitch to the whole thing so water will better drain off of it.

Hi tom,

Long time!, glad to see you're still on the board (of course I'm not always on myself--no matter what people think! :)

How goes "THE PROJECT?" Just curious!

OK, I guess that's a subject for another post...but I can't help asking for a "reader's digest" version!

BTW, I like your comments about decking in general for this post. Take care!

Regards,
-k2 in CO

Moderator, Miscellaneous Forum

http://www.bobvila.com/BBS/Miscellaneous

project has been on hold for a bit, but will resume shortly.

i do roam the board every other day or so, and try to chime in where i feel i can help some.

see ya in the cellar soon, haha...

A quick note on spacing:

MOST of the claims I'm called out on revolve around decks that had been spaced when they shouldn't have. Each case really is different. On decking with high moisture content (freshly treated), it's a good idea to butt the pieces up (as homebild recommended). On decking that hasn't been freshly treated and has close to equilibrium moisture content (that of your surroundings), then it should be spaced.

There's no hard and fast rule to this- it's all about moisture content. When we treat lumber, we can swell it as much as 8 to 10 percent. Now that CCA is history, we don't have to let freshly treated lumber languish on drip pads waiting for fixation to occur. That means that lumber yards who traditionally keep low inventories often have lots of PT around that is freshly treated and of high moisture content. The old rules don't apply anymore.

Would that be insurance claims Jay?

In any case, if the decking has the very moisture content it will retain the same consistency during the wet months and expand to that (or more) width.
Placing that decking with no spacing is again, going to create problems, you need to space the decking to the moisture content as I mentioned...
If you feel the decking is an abnormaly wet and heavy at the very least use a 1/8.


http://www.altereagle.com/
http://decks-ca.com
http://kingofcrown.com

Alter Eagle Construction & Design