I’m going to be building a small deck with what Lowes Home Store calls ‘severe weather pressure treated” 5/4 x 6 x 8ft deck boards. The ‘details’ on Lowes’ website say to ‘install boards tight together’ (see attached). For any who build decks for a living–have you ever seen this rather than what I thought was normal to allow a (+- 1/8″) gap between boards for expansion when wet.
Thanks
Howard Smith
Newark, DE
Replies
You be the judge. If the treated decking is wet and heavy we lay it with no gap. If by chance you find DRY treated decking that isn’t twisted and curved, you could lay it with a gap and expect it to expand a bit.
How much? Hard to say w/o seeing the product.
Thanks Calvin,
Do you know if pressure treated lumber is or is not 'kiln dried' (to a 19% moisture content)?? I haven't used PT lumber much--but it is very wet even in the home improvement store-so assuming it is not kiln dried.
I have not used my meter as every stink’n time I’ve used PT decking it was damp to touch and HEAVY. Thus, my experience told me to not space it.
I would concur with oldhand and j .
If you have a moisture meter you can see how wet it is. I’ve always installed it tight, I hardly ever encounter a treated board dry enough that it will not shrink. I know it can be hard to believe, but the wood will shrink about 1/4” (sometimes more). If your PT is just as wet as the stuff I get, it’s going to shrink. With all the shortages of PT I would not doubt the stuff getting sent out of the mill is quite wet as they are probably starting to speed up production and not allowing for a lot of dry time. Treated wood is notoriously wet. So much so that you often need to let it set for a year to dry before any stain can be applied. There are some specialized stains that can work around the wetness a bit, but most stains will not work well until the wood is dry. I’ve been building decks off and on for just over 20 yrs, always installed treated tight and am happy that I did. When I go back to the same decks years later, there’s definitely enough gap.
Thanks jlyda
Do you know if pressure treated lumber is or is not 'kiln dried' (to a 19% moisture content)?? I haven't used PT lumber much--but it is very wet even in the home improvement store-so assuming it is not kiln dried.
Typically it is kiln dried before treating at which it swells up again. With syp if it dries out after treating [air] it very often goes to warp/ twist city. That's why you need to use it before it re dries.
There is a grade of kdat which is kiln died after treating but I've never seen or used it.