Pressure treated wood or not?

ejb · Jun 9, 2007

Hi guys.

I am going to finally put a floor into an old outbuilding of mine that currently has gravel/dirt floor. Never gets wet in there except normal ground dampness (its on a high spot).

The building has cinderblock foundation so I am going to use thru bolts to attach a 2x10 ledger board all the way around the inside, and a couple of 4' piers in the middle to support a carrying beam, and then frame the joist much like you would a deck (2x10's 16oc). Question is, how bad would it be to NOT use PT wood? There would be no ground contact, and all the wood would end up being about 8-10" off the ground. I would cover the dirt floor with plastic to keep the moisture down, but wonder how well this would hold up for 40-50 years? Seems to me it shouldn't be a problem....opinions?

Of course PT is probably better, but the extra cost and weight(during construction) is a factor...

shvl73 · Jun 9, 2007

I would vent it by knocking out a couple of blocks and install 8x16 vents on opposite sides to get some cross ventilation.

Cliff_Johns · Jun 10, 2007

I would suggest you use PT for the ledger board at least. Personally, I'd use PT for the joists too. For the floor itself, regular stuff will last just fine. If you use plywood, it will contain the moisture though, so venting it would be a good idea.

Cliff

VABlue · Jun 10, 2007

I'd also put a vapor barrier over the floor. Even with cross venting you could get some mold growing on the non-PT stuff if the dirt floor remains damp. Otherwise it should be fine. My old house had a dirt floor crawl space and the floor above it was not PT. It's held up fine, despite a lot of ground moisture coming through the crawl space (the house is in a low spot). Good luck, sounds like you have some fun ahead of you!

fishpick · Jun 11, 2007

ejb-
I'm planning on the same thing for a portion of my barn - to make that end a wood shop - and keep the other end for a future concrete floor for car/tractor/vehicle in general - work...
Attached is a cross section of a post - sound the same as your project.
I decided long ago in the initial thoughts about this that PT (although nominally more) is a lot better way to go for years of life.

My plan is to actually dig some trenches that the 4x4 posts and the 2x12 beams will be sitting in... the top of the concrete pier that holds them will be well below that actual grade. One the piers are in and the posts are attached - the trenches get lined with heavy plastic to ****** the water dampness of mother earth from working its way up. From there the 2x12's will get attached to the posts... then 2x12's get laid on as joists... all PT.
Certainly the ends will be vented...
Going to run lots of electric... lots of dust collection pipes...
Then between the 2x12 joists - I'm blocking them and them placing 2" foam board on the blocking for insulation. Then the top is going to be 3/4 TG ply - the stuff that is "moisture resistant" - not PT.

VABlue - I'd be a little concerned - even with cross venting - about having 2 layers of moisture barrier... for the same reasons you don't do that in a wall...

VABlue · Jun 11, 2007

Agree, guess I was unclear. I put the vapor barrier over the dirt floor, nowhere else. What happened in that crawl space was moisture seeped in and built up around the slab of the basement floor (half crawl space/half finished), eventually passing under the wall and into the carpet padding of the finished part. The trick was to put a french drain pipe in around the perimeter of the crawl space, and a vapor barrier over the dirt. That kept everything dry inside the crawl space. The drain pipe (w/sump pump) dried up that basement in a hurry. Wish I would have done that years earlier, I could have better enjoyed the pool table and wet bar...

SPIKER · Jun 11, 2007

Not sure but is there a reason you don't want to concrete it?

I know it is a much greater expense in $ but in long run it is cheaper for maintenance and durability. also in time involved (you're time that is) in building decking piers ect vs simply re-grading if need be and pouring over good vapor barrier & possibly insulation if heating is planned. even adding radiant heat is not all that bad if done as part of the project. this is also means that you won't loose any HEAD room and could/will add value to the property, more than a part floor made of wood will that is.

if you are intent on wood then, by all means I would use treated for anything contacting block/concrete or ground! this also means using the Stainless Steel fasteners there on all those connections as well. I bought a place that the guy built things CHEAPLY and it is a mess 10 years later every thing is roting & falling apart! One shed is similar to what you are doing and the floors are rotted to the point I'm 2/3 afraid to walk in there already broke through in a few places. he used plastic sheeting under it and wood above , std plywood floors and 2x10 s as joists spanning ~12' it is very warped and as mentioned full of mold & rot. not sure if I'll even TRY to save it...

One other shed which was newer (built by him) I already Jacked up and poured concrete under it and re-attached it to the new crete and it is 100% better... I posted in projects forum with pics last fall about it.. look under my id for it if you want to see... the garden shed I'm talking about tihe wood floor may make pouring crete inside a lot harder but I may also be able to move it to a better location prior to repairing it all.

Mark M

fishpick · Jun 11, 2007

SPIKER - Here's my reasons for my design - in no particular order...
* Wood floor is much easier on the legs and back - so for wood working or anywhere you will be on your feet for long periods - it's friendlier.
* In a wood shop - should you drop a piece - a wood floor does not equal the potential disaster that concrete does.
* There is a lot more flexibility in moving things around under the floor with wood than poured concrete - like a new power outlet for a new tool - or a new dust collector run.
* Way cheaper for wood system - and if built with PT stuff - and built correctly - it will last FOREVER... All the old barns of past were big heavy wooden floors... and they are still around.
* Some day - certainly - the front of the barn will get concrete for old truck / tractor restoration projects!

ejb · Jun 11, 2007

For all the reasons fishpick states, I am also planning on wood floor (mine will also be a woodworking shop). I considered the cement and decided against it because a) I can't do it myself and b) I was afraid it would always feel damp inside and woodworking tools and dampness don't mix.

Sounds like I'll be going PT all around after reconsidering. Don't want to have to do it all again in 20 or so years.

What options do I have for insulating the floor? Can I put down the joists, put down PT plywood, laydown 4x8 sheets of rigid insulation and then another layer of plywood? fiberglass bats inbetween each joist is a pain to do, and also will likely turn into nests for all kinds of critters...

fishpick · Jun 12, 2007

ejb - I'm right there with you on the fiberglass in the floor... BAD idea. I have seen systems where people have a concrete floor poured - over a vapor barrier... then they lay 2x4's on their side every 2' and place rigid insulation and wires in there... then they top it off with 3/4 TG plywood... I would think you could do that over a plywood floor... BUT - then your price is approaching that of concrete...

My plan is to cross block the joists and then place 2" rigid insulation on the blocking... then the 3/4TG ply over the joist tops... sure - it's not airtight... but it's a lot better than nothing. It should help hold the heat (since heat rises - and keep the floor from being icy cold all winter.