A few years ago, I had one of those “portable” storage sheds built in my backyard for housing my tools, lawn mowers, etc. and has a pressure treated plywood floor for all the obvious reasons. I’m now considering building another shed like this (only bigger – 16’x20′) to use as a hobby room and maybe even throw in a couch and tv just to “get-away-from-it-all-for-awhile”. A concrete pad is nearly logistically impossible (can’t get a cement truck anywhere close) and basically cost prohibitive. The the flooring system will like the other building; a standard joist system supported on blocks with about a 6″-10″ ground clearance. Since the underside of the plywood will be exposed to moisture, I’m assuming I should use pressure treated again. However, since I will be be spending much more time inside this building than the other one, I’m concerned about exposure to the PT chemicals and breathing any fumes the wood might give off. So my question is this: (finally!) 1) Do I even have to use PT plywood or can I use non PT and just treat the underside w/ a water sealer before installing it? 2)Assuming I have to use PT, if I put down a layer of standard plywood over the top of the PT, will it effectively block the exposure? What do you guys think of this? I value your ideas!!
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16x20 hmm. Sounds kinda big for a "shed" Any building code enforcement in your area? They might have something to say about your shed.
My 1st thought was to simply pump concrete for a standard slab, but the costs can mount.
Many a house has been built with PT foundation walls in the crawlspace (with and without vents) and I haven't heard any adverse comments. Put some underlayment flooring and a chunk of vinyl down and that would likely help significently.
But you know this is a shed and if you build it like a shed than it is going to be a shed (pretty deep, huh). It ain't gonna be living space.
Water sealers would probably not work out in the long run.
What kind of hobbies?
Thanks for the input guys!
The building codes here really aren't that restrictive. Just so long as it's so many feet from the property line, directly behind the house, etc., etc. As for size, any storage shed or garage can be up to 2,000 sq. ft. I believe before the restrictions get tighter. (Yeah, I was surprised too when I called and asked.) There's also that "portable" designation too - add a concrete floor and it's a whole new ballgame.
My first shed is a 12x16 that I bought from HeartLand Homes and is only a few years old. After watching 1 guy build this thing in a single day (albeit w/ many pre-cut pieces) I knew I could do the same thing only bigger and better in a few weekends.
Anyway, as for the PT question, I just assumed that since most of these buildings come w/ pt floors, that's what is needed. Given the ground clearance, there's decent airflow so moisture build-up shouldn't be a problem. Maybe what I'll do is just install the PT subfloor, cover it w/ a plastic vapor barrier, then add a 2nd non-pt floor system (2x4 joists w/ insulation.) That way I get the best of both worlds.
As for hobbies, mostly it's model trains and airplanes. The problem is, like most of the other homes in the neighborhood, I don't have a basement for this stuff which would be ideal. This way, I can have my private place to play w/ my toys, watch Nascar, etc. And as for future re-sale appeal, it can also be a great play room for kids on a rainy day. I'm certainly no tree hugger but you see my concern regarding exposure to this stuff.
Why will the bottom be exposed.
I don't know what your climate it, but what about insualtion?
i've been cutting treated & picking my teeth w/ it for 30 yrs, my bird houses are made out of it. bulk heads are made out of it. the whiners & enviro whacko's have got everyboby beleiving in the boogie man. g i v e m e a b r e a k, please.
sawman- they're comin' after the fiberglass in your walls...
tanks alot for de warning rez, beers in the cooler, burgers on the pit.
...and watch out for how much smoke yer barb pit puts inna da air. you must live out in da country where dey still let you smoke cigars in your own house.
Put in a 14x18 pad for a shed with concrete floor, pump cost about $350.
bobl Volo Non Voleo Joe's cheat sheet
The problem with the concrete idea is that access is hard, or so he said. My brother gets terrible migraines from cutting PT wood. We are builders and work in alot of indoor areas and he doesn't get those headaches at other times. The PT stuff smells really strong, and contains arsenic, which I hear isn't good for you. They are actually discontinuing use of it and will be using only copper based treatments on wood fairly soon i've recently read.
I don't think you need to use PT ply if you have a frame on blocks above grade. Treating the wood thats closer to the ground may be good though. Perhaps a vapor barrier below the traditional ply. Where do you live? What destroyed the previous shed?
My access was impossible for a truck too. That's why I pumped the concrete.bobl Volo Non Voleo Joe's cheat sheet
There are small concrete pumps that can be pulled behind trucks, that don't cost that much to rent. A concrete sub used one at my place to pour a slab in an "impossible" location. So maybe a slab is an option.
With that little ground clearance, unless you live in an arid area, yes I'd use PT joists and PT plywood.
The PT plywood I've seen, the foundation-grade 0.6 pcf CCA stuff, is usually pretty dry (maybe it's KD after treating?). I wouldn't worry about it outgassing anything. Remember, things like particle board and OSB outgas, too. And you're going to cover this with vinyl flooring are something similar anyway, right?
As long as you have this up off the ground and don't block the ventilation air flow under it, regular 3/4" ply should do fine. There are a multitude of homes from Florida to the Maine woods built like that and the greatest rot problems occur at poorly set and trimmed thresholds/doors, not from under neath.
However, in parts of the country, carpenter ants, powderpost beetles or termites make a good argument for using PT plywood.
The dangers from CCA PT are vastly over done but they absolutly have nothing to do with breathing fumes. Copper, Chromium, and Arsenic are heavy metals that leach down into the ground without floating around in the air for you to breathe. They ar ebound to the wood and each other in a way that they are not dangerous to humans unless a reaction caused by exposure to heat or acid releases the arsenic.
Friction from a dull saw blade can release it in dust particles small enough to breathe so some carpeners get reactions while working with it.
Children on playgrounds sometimes chew the wood so the acids in their saliva can release some arsenic. I suppose tooth picking falls into the same catagory but on the other side of the coin - cyanide and arsenic are elements used in some cancer treatments. They can be found in minute amounts in the seeds of fruit and some nuts you eat.
Acid from a manure pile or acidic soil in gardens can release the arsenic also.
I'm wishing they wouldn't pull the stuff off the market and that we could just learn to work a little smarter and choose where to use it a little more carefully.
Piffin, I agree. There are 2 PT plants near me (within 12 miles) so the stuff is plentiful. It's not a fume issue at all. The worst exposure is cutting it and handling it when it's fresh. Most of what is going to leach out is done in about 3 years. Like the big Asbestos furor, what isn't hype can be mitigated by common sense and using precautions.
My local inspector (who can be a hardass) lets me use it for subfloor in bathrooms, porches, laundry rooms, etc.
To the original post; a lot of of moisture damage can be prevented by a ground vapor barrier.
Measure it with a micrometer, mark it with a piece of chalk and cut it with an axe.
Edited 4/25/2002 9:23:25 PM ET by Notchman
Edited 4/26/2002 12:03:58 AM ET by Notchman
Now there could be a slight problem with fumes if you lived within a mile or so of the plant. I used to live near an LP plant. The problem was with formaldehyde in the glues though and not connected to the PT chemicals.Excellence is its own reward!
If this is going to be a big boys' hangout shed and you're concerned about exposure to arsenic from PT material, why not use something like Trex for the flooring ?
I would still use some sort of vapor barrier on the ground beneath the flooring.