Floor joists - off topic sort of

[Fred Voorhees]

I know that this is kind of out of the way of the norm for this forum, but I knew that I could come up with expert opinions regardless. Quite simple really. I am just about to begin laying floor joists in my old attached garage to level out the floor. I had always planned on using pressure treated lumber over top of plastic sheeting to protect against any moisture that could possibly migrate up through the concrete floor.

My question is this. Do I really need to use pressure treated lumber? My thinking is along the lines of:

1) With a continuous film of plastic sheeting between the concrete and the joists, is it necessary to use pressure treated?

2) My biggest concern is the real possibility of the pressure treated lumber to warp and twist, and thus, throw the level of the floor out of kilter and make the flooring job that much more difficult.

3) If I could use regular dimensional lumber, I could rip it with less worry about the damaging crap in the air while I cut it over cutting the pressure treated lumber.

4) With it being the weekend, I doubt that I could get an answer on this locally, but could it possibly be a code issue to use pressure treated in a situation such as this?

Appreciate the help guys!!

[Jason Roehl]

How old is the concrete? If it's more than a few month old, you're not going to have much moisture migrate through. Use duct tape and tape a 2'x2' square of plastic down on the concrete (totally seal the edges with the duct tape). If you don't see condensation in a couple days, you probably won't.

I don't know too much about the code for this situation, but I would skip the plastic. The code DOES say that you need to use PT lumber anywhere your lumber comes in contact with the concrete. You could just lay PT 1"x3" sleepers flat on the concrete then go with whatever size SYP joists run perpendicular to the sleepers. I don't believe the joists would have to be very substantial since the concrete would be bearing and distributing the weight.

[Kelly C. Hanna]

I sure would. I never put any untreated lumber down on or near to the concrete. Cement can wick up water anytime the water table is full. I would also go with the plastic moisture barrier. You sure don't want the wood getting damp and rotting prematurely. Plastic is cheap.

[Mark Singer]

Any boards in contact with the concrete must be PT . If you use PT plates to support the joists , the joists can be regular lumber. I don't know how the detail is. When you frame walls, only the bottom plare is pressure treated. I built a Bocci Court and use all presssure treated since it was in contact with the soil.

[Jim Becker]

Fred, I'm with Kelly on this one...you know how wet your property gets right at the surface and I can assure you that the concrete floor is going to get some of that wicking up from time to time. I'd do both the vapor barrier and the PT joists, or at least PT sleepers with fir joists on top. It may be more cost effective just to use the PT joists.

[Michael Perata]

1) With a continuous film of plastic sheeting between the concrete and the joists, is it necessary to use pressure treated?

Making a floor system like you are describing means you are typically enclosing each joist bay with no ventilation. Even with the moisture barrier down, there will be ambient moisture that will be trapped and will grow mushrooms and other nasty stuff. DAMHIKT, but I do and it cost me a lot money for the education.

In cases like what you are describing, even normal PT wood is not recommended. There is a more lethal form of PT lumber that goes by the designation of AWPA LP22. This is very nasty stuff but is the only treated lumber rated for totally enclosed damp locations. Lumber over a concrete floor is classified as a damp location.

The alternative is to ventilate each joist bay if outside air can had, or to mechanically ventilate if outside air is not available.

Note: This is the "correct" way. Few people do it this way to their own house/shop.

[Fred Voorhees]

Fred, I'm with Kelly on this one...you know how wet your property gets right at the surface and I can assure you that the concrete floor is going to get some of that wicking up from time to time. I'd do both the vapor barrier and the PT joists, or at least PT sleepers with fir joists on top. It may be more cost effective just to use the PT joists.

As I said, this method had always been the original plan and that is the way that it is more than likely going to be done. I think I'll run everything past the local bldg inspector this week and see what they say. And yes, we both know that I have a high water table in this area (just looking out the windows today confirms that). However, I have never experienced one bit of water in the garage in the twenty years that I have lived here. No matter though, as Kelly says, Plastic is cheap. Got the strings strung up this morning and planned on hitting the stock car races tonight, but they are rained out so I guess I can get a bit more planning done out there. With the strings up, I can at least determine what size joists I now need and get a quick idea of how much it is going to cost me.

No races tonight means (I guess) that Karen and I can get out to our overdue 14th wedding anniversary dinner tonight. YEAH!

[Arvin Brown]

Why not just use a cement based concrete leveling product? Here is a quick note on it:

http://doityourself.com/concrete/lev...n_concrete.htm

[Jim Becker]

Why not just use a cement based concrete leveling product?

Fred would have to pour it nearly a foot thick at the front of the room! The floor is coming up more than just a smidgin...

[Kelly C. Hanna]

Congrats on your 14th Anniversary!! We're sneaking up on our 7th this year (I didn't get married until I was 41).

[Roger Turnbough]

Fred,

I'm a bit curious. As to why you would want to put sleepers over a bad floor in the first place. I dont know the size of the area that you are working on, but, why not rent an air powered jackhammer and compressor, take out the old floor and pour in a new level floor to begin with?

I did some extimates just as an example.

Say your space is 24x24 and you pour a 6" slab. That equates out to 10.67cu yds of concrete.

If you went with 5" of concrete that would equate out to about 8.5 yds.

Using $75 as just a base estimate, the 10.67 yds comes out to about $800.

The 8.5 yds comes out to about $637. Now those are just material costs. You would still have to pay truck and driver time.

Now figure in the cost of renting a compressor and jack hammer at around $200, and then another 300 roughly for the cost of a large dumpster and you are somewhere in the neighborhood of $1300 for a new concrete floor, pitched towards the overhead door. Almost forgot to figure in the cost of a load of gravel probably another 300, but dont know for sure what 20 tons would cost.

If wanted you could also deepen the slab down the center or wherever and form a trough in for dust collection and what not.


Using the same 24x24 building as an example, you would need approx. 11 Joists assuming that you could cut these on a taper and get 2 tapered joists out of one regular joist. So, lets use 24' Douglas Fir 2x12 joists, lets use $50 a piece for the joists, (cant find a good current price on the net). Thats $550. You'll need 528 lineal Feet of 1x3 pressure treated lumber. Lets figure 12' pieces, comes out to 44 pieces at a guesstimate of around $10 a piece. Thats $440. One roll of heavy plastic sheeting. Roughly $50. 200 Tapcons, 2 1/4" long, roughly $75.
Ok so we still need T&G plywood of some sort. I wouldnt use OSB sheeting for this application, but at least Yellow pine or Fir, 3/4" tongue and groove. You need 18 sheets. Dont know the current price of this either, but will use $25 as a safe estimate. That comes out to $450.

So lets add this up.

Joists $550
PT 1x3 $440
Plastic $50
Tapcons $$75
T&G Sheeting $450

Grand total of $1565.00

So for comparison, we came up with a sleepered flooring system for somewhere in the neighborhood of $1565.00

Concrete floor comes out to $1600 approx.

$35 difference in price. To me at least its a no brainer. You must understand though, these prices are just estimates, I didnt call around and get prices on anything. Just used what I thought was close.

You can get all kinds of Great estimators and calculators here

http://www.cyberyard.com/calculators...alerid=&view=1

Anyway, wish you luck on your project, and hope it comes out well for you.

Roger

[Jim Becker]

I'm a bit curious. As to why you would want to put sleepers over a bad floor in the first place.

All good questions, Roger and I'll let Fred answer them specifically. But my observation is that this is not a situation of a "bad" floor. He's converting a former garage (with what appears to be a good, solid concrete floor but with a slope) to living space. A wood floor will be more comfortable on the feet and he can get it to the level most appropriate to join up with his other floors in the home.

[Mark Angle]

Check out FINE HOMEBUILDING mag. If I remember correctly they had an article about wood flooring over concrete just an issue or two back.

[Hal Flynt]

FYI Often I find pressure treated SYP cheaper than non treated SYP.

[Fred Voorhees]

Just for everyone's information, I did order PT SYP - enough for the entire job. 25 2X8X8's 30 2X6X8's and 22 2X4X8's. Also a roll of plastic for the moisture barrier and 18- 3/4" 4X8 sheets of T&G OSB for the underlayment/decking. Total bill, with a 10% discount included came to $939. Hope to get started within the next day or two.