Treated plywood – overkill in this application?
Situation: concrete slab, 6-12″ of slab exposed above grade, resting on 4″ of gravel and a sheet of plastic. I’m putting down a plastic vapor barrier and screwing down 1/2″ plywood (all of this to get a little elevation for drainage where the door abuts on a brick patio). Screwholes will get a shot of poly caulk before the tapcons are driven. All of this inside an enclosed space.
Space will be used as a studio with occasional overnight guests. A floating laminate floor will go on top of the plywood, over the usual thin foam underlayment.
I was planning to put down treated plywood, but am wondering if this is overkill. I realized today that, if I trust the vapor barrier at all, it should be enough that regular CDX ply would be fine, with less outgassing of fumey junk in the occupied space.
Help!
Replies
no treated
I would certainly not use treated ply in an enclosed inhabited space. And I question the need for the vapor barrier below the floating floor. Wouldn't the vb under the concrete be sufficient to keep the slab dry?
I would agree to
"I would certainly not use treated ply in an enclosed inhabited space."
I subscibe to this philosophy as does my local building department.
However......................
I have been to New Orleans 5 times since Katrina, 4 of those trips we were building for H4H. Houses we worked on were all elevated roughly 4 feet above grade. All first floor subfloor framing was ACQ treated and the first floor subfloors were specified as.......drum roll....... 3/4" ACQ treated, T&G, plywood.
Go figure.
Jim
Side note ... replace all your words "vapor barrier" with "vapor retarder". With most e.g. poly plastics, it is NOT a barrier to moisture migration. It actually has a tested rate of moisture migration. Aluminum foil I believe is the only thing that could be considered a "vapor barrier". The industry has shifted from your term to the one I suggest ... and for good reason.
just an FYI as you think about moisture, etc. Other's will give you words of wisdom on the specifics of your question.
I used some pressure treated plywood exposed in my house. No mention by the BO about it. It wasn't a big area, but it was there non the less.
Perhaps
a hold over from CCA treatment days.
Our local BI's do not want any treated wood inside of a living space with the noted exception of the mudsills.
Don't really know the rationale behind this, paranoia about gases maybe; I just know it has been their policy for years and did not change with the advent of ACQ, MCA, MCQ, etc.
Jim
As far as I know, none of the common treatment methods in the past or present has an outgassing hazard to any degree. I can see restricting treated wood to non-finish areas, but I don't see the point in prohibiting it.
(I hope that, in addition to mudsills, they also allow it in bottom plates on concrete.)
Not very many
slab built houses in this county, but yes, bottom plates on concrete are OK / required.
Jim
No basements?
About
90% basements or 1/2 basement + 1/2crawlspace, 9% full crawlspaces, >1% slabs unless a garage or some other type of outbuilding in my county. Beach and coastal areas are usually raised crawlspace of some sort - some are raised pretty far too! - many of these are built on PT pilings.
New construction in my county = 80% poured concrete foundation walls; full crawlspaces are usually concrete footings and run up in block rather than poured. Minimum footing depth = 32" here.
Local BI's require PT wood in contact with masonry of all foundation types either poured or block. Also whether a sill or a bottom plate.
Jim