I’m putting a 21’x14′ extention on my shop over a concrete slab. The
guy from Menards told me to lay 2×4′ flat over the slab on 12″
centers; then, cover with 1.5″ foam insulation sheets; then, 3/4″ T&G ply.
Does that sound right to you guys who know about this stuff?
I’ve got a 1500 lb. planer; 500 lb. jointer; and 1000 lb saw going in this area. I just want to be sure the floor can handle them and stay level with no dips.
-Thanks
David
Replies
FWW Shops and Tools issue, I think the 2003 Eddition, provides plans for doing just that. It looks like a good system. Maybe someothers around here have actually used the system.
I read the article in FW but it had the foam insulation going between the 2x4's rather than accross the top. That's the thing that was spooking me.
The comments here are making me feel better about things, though.
Thanks
I just added to message #3. Should have made it a new post. Didn't realize you would be reading the responses so quickly.
Sorry, I didn't read close enough. I put the styro between the sleepers not over them. I would be leary about over the sleepers. Wish I had the ability to make the sleepers taller so that I could run dust collection under that floor instead of along the walls. I used one of those .22 blank nailers periodicly to hold them down, 2x4's just aren't what they used to be.
Brian
I can't provide any numbers, but extruded polystyrene can take quite a bit of load if it's evenly distributed, and 3/4" ply is stiff enough to do a pretty good job of distributing the weight.
If you're not comfortable with that, and you're pretty sure where your machines are going to sit, you could add a second layer of 2x4's at right angles to the first layer, just at the machine locations, and piece the insulation around them. That would eliminate dips even with much larger loads than you've described.
If you don't want the thermal bridging even under the machines, another possibility would be to use 1-1/4" plywood instead of 3/4". That would increase the stiffness by a factor of 4.6.
Still another possibility would be to use 2x2's instead of 2x4's, install foam between them, add more 2x2's at right angles, with foam between them, topped with 3/4" ply. The result would be somewhat higher material cost for the extra foam, extra effort cutting and piecing the foam, probably better thermal performance, depending on the relative R-values of the foam and the 2x4's, and very high stiffness. You would also have to account for any moisture issues with laying foam directly on the concrete. (The guys over at Breaktime might call this a Mooney floor. (Search the BT archives for Mooney wall to get the inside joke.))
Edited 3/9/2004 11:24:21 AM ET by Uncle Dunc
David, That is almost exactly what I did in my shop except that I put a layer of plastic sheeting for a moisture barrier before I put down the t&g ply. No problems at all except that my legs and back aren't nearly as bad now as they were before I did it and spent all my time on concrete ;)
Brian
You can definately use 2x4's w/rigid insulation & 3/4 t&g. I have done many basement remodelings and used the above on a few of them. It will support your machinery with no problem because much of the weight will be transfered to the slab. Are you putting anything on top of the plywood?? A wood floor perhaps? Only wondering if the plywood will get dinged up with time....
Wasn't planning anything on top of the ply.
So if I understand...
1. i should put down plastic
2. then the 2x4 sleepers on 12" center
3. then cover 2x4 with 1.5" rigid foam
4. then cover foam with 3/4 T&G.
Do the sleepers need to be "shot" or can they just float?
-David
>> Do the sleepers need to be "shot" ...
I can't imagine what lateral forces would tend to move them. Cheap peace of mind, though. Putting foam between them would hold them in place just as well, and enhance thermal performance at the same time.
I think the foam is supposed to go between the sleepers, not over them.
If you're worried about thermal bridging, consider putting down some of the thin foam underlayment used for strip flooring. Put it on the slab in lieu of the poly.
12" OC sounds like overkill to me, wouldn't 16" be plenty? The T&G should bridge that just fine, if you nail it off properly. (Remember the sleepers are flat, not on edge, so the span distance is less than for a regular joist floor. And with the rigid foam, you probably could even go to 24" oc. )
Don't think you need to worry about shooting the sleepers into the floor; once the deck is on there's no way they can move.
Only other thing I can think of to worry about is traction. I've noticed the plywood in my shop is getting slippery in places - especially if there are shavings or dust on the floor. Not sure just what to do about this."Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
>> wouldn't 16" be plenty?
If your assumption about where the foam goes is correct, yes, 16" would certainly be enough. If the foam really does go over the sleepers, I think 16" might still be enough, but I can understand why someone might be concerned about deflection with that arrangement.
Edited 3/9/2004 4:25:54 PM ET by Uncle Dunc
My floor is 1 1/8" t&g subfloor over 2x4 @ 16" OC and I still get a bit of deflection when moving the Unisaw w/50" fence, router, drawers for saw & router accessories. The 2x4's are tapcon'd to the floor & ply is screwed to 2x4's so I know none of it is moving! With tools of that weight I'd support the 12" spacing. I do share your question about the foam on top of the 2x4's - just doesn't "feel" right.
I have just finished insulating my basement shop, and a sun room using mostly XPS; Extruded Polystyrene insulation. XPS provides an air barrier, but will allow moisture to escape. For this reason it is approved for direct contact with concrete, and is used that way when installing it in basements, or on floors. Three ways you can get moisture on your floor: wicking, condensation, and cracks. Wicking (not the technical term, BTW) occurs when moisture from the soil below your floor is sucked up through the concrete and into your basement. You can test for this by taking some plastic to your concrete floor with duct tape, and checking if moisture forms underneath. You can remedy this by painting your floor with drylok before you install your floor. Condensation happens when warm house air hits the cold concrete floor, and the moisture from the air condenses on the concrete. The concrete will be colder when it is insulated, so this will increase condensation. This will only happen if you have a leaky insulation installation. By putting down XPS, and butting the sheets close, or sealing the seams, you will prevent the house air from reaching the concrete in the first place, and also improve efficiency by preventing the air leakage. Cracks that let in water are usually apparent, and must be plugged with a hydraulic cement.
The XPS has a compressive strength of 50PSI if I remember correctly. I will try looking it up tomorrow. I would paint the floor with latex Drylok if you think you will have moisture problems, plug and cracks, and place down 2" XPS sealing any gaps in the seams with great stuff to prevent leaks in the air barrier. I would place the XPS directly on the concrete, and put down 1x3 or 1x4 sleepers to support the 3/4" plywood. 12" OC would be overkill for a room, but where heavy machinery is concerned, it would be preferred. There is no benefit to using 2x4s vs 1x4s for the sleepers, as it will only take up more space. The 2" XPS will be helpful if you live in a cold climate. It costs more, but not much, and it is your time that is most important anyway.
The sleepers can be fastened, but I don't think it is required by code. I used some liquid nails when I did this to keep them from snaking away from me. Another option is to level your floor with the sleepers. This is a bit more work, and harder, since you need to basically resaw each of your sleepers so that when laid on the floor, they are level.
If you insulate the walls as well, make sure the insulation on the walls extends all the way down to the insulation on the floor, and not only to the top of the plywood subfloor.
Many houses are built with the slab poured on top of the XPS, so putting it directly on the floor is not a concern. Also, a moisture barrier is not required with the XPS, as moisture will be allowed to escape through it (air will not). If you have EXCESS moisture, then I would seal the floor with drylok, not poly.
This was longer than I had planned, but hopefully it'll help.
Tom
PS, you don't want to fit the XPS between the sleepers. Trust me on this.
Edited 3/9/2004 5:09:57 PM ET by big country
I put down a plywood floor and I'm glad I did...easy on the back and dropped tools. Also, it makes clean up a breeze. Here's my suggestion:
Good luck with your project.
I'm with everyone else that this sounds like a pretty good solution. I would also consider putting the dust collection in the floor if at all possible though. There has to be some way of getting a smaller, wider duct in there to pick up dust. even if you only got a boot right next to the wall and immediately converted to 4" you could at least sweep all of your dust and shavings into a floor pan and away it would go.
Good Luck
Rob Kress
Judging by the weight of the machinery,I'm guessing they will be stationary. If you have a location picked for each, you could form up an area for each one, and pour concrete pads. Use wire mesh in the pad. They seem like they would be small enough to do the job with a rental mixer. Vapor barrier is a must, and use good quality pressure treated materials.
Thanks to all for your quick and helpful comments. I'm anxious to remove myself from the carpentry and get about woodworking. From everyone's comments I feel safer putting the extruded between the sleepers; and at least use liquid nails; but probably a mechanical fastner as well.
I'm not sure of my final layout; so I'd be playing "Russian Roulette" trying to guess at it; I'm sure I'd get it wrong.
I've always thought about in floor DC; but my runs are 6"; and I'm not sure of my final layout anyway.
Lots and lots of great information. I can't thank you all enough.
-David
Your guy from Menards is not wacko. Foam between the 2 x 4's and the plywood will easily support the load. Look at the numbers.
With 2 x 4's laid flat 12" apart, each square foot of plywood will rest on 42 square inches of 2 x 4. So there will also be 42 square inches of foam supporting each square foot of plywood. Suppose your 1000 pound saw has a base of 3 feet by 3 feet, that's 9 square feet. The 9 square feet would be supported by 9 times 42 = 378 square inches of foam. 1000 lbs spread over 378 square inches of foam is only 2.6 pounds per square inch. Underlayment foam can be purchased in compressive strengths ranging from 15 to 100 psi, depending on what you buy. So, you'll have way more strength than you need, if the saw is evenly supported.
You can work it backwards, too. Suppose your saw is supported on 4 legs. Then each leg would hold 250 lbs. Suppose each leg concentrated the entire 250 lbs on an imaginary square of the plywood about 3½ x 3½ inches square, or 12¼ square inches. 250 lbs. divided by 12.25 square inches = 20.4 psi, so any foam rated over 21 psi compressive strength would work.
Simply select a foam rated for underslab use with a rating over 21 psi and you'll be fine.
My Menards guy had said to put the foam "over" the sleepers, rather than "between" them. That was my concern. I knew the FW article on shop floors had specified putting them between. Hence, my confusion. confused.
-David
Yes, over the sleepers, that is, sandwiched between the sleepers below and the plywood above, is correct. You'll get the best insulation value that way, and, as my calculations showed, you won't crush the foam if you get an underlayment grade foam with a sufficient rating.
Oops. My error. I misread your comment. I'm not sure which extruded i ordered; i know i didn't get the lowest grade (the white stuff that is very flimsy). Now that i have psi numbers i'll calculate it.
Thanks again,
David
Actually, the white stuff isn't extruded polystyrene, it is EXPANDED polystyrene. It has lower strength, cost, and R-value, and is a very different product. XPS is XPS, so brand names just have different colors; no difference in product.
Tom
Not to be critical and realizing that your calculations were likely of the back of the envelope type, but it appears that your calculations only consider uniformly distributed loads and ignore highly localized loads, such as , for example those caused by teh wheels of mobile bases or open equipment stands. For example, for a 400 lb. saw on a mobile base, with four wheels equally spaced about the center of gravity, each wheel is supporting 100lbs - the contact area between the wheel and the floor is less than 1 sq inch which leads to a local bearing pressure of over 100 psi at the contact point between the wheel and the plywood floor (admittedly, this is a very rough calculation and I'm not sure how much is transferred to the foam underneath). For a contractor type saw with formed sheet metal legs the bearing pressures probably get much worse. Because the plywood is flexible the relatively high localized bearing pressures may allow the crushing of the foam underneath. Depends on now much the plywood deflects, with each subsequent local crushing of the foam that area of the floor will deflect more, resulting in a larger region of crushed foam, until the vertical movement of the floor is solely constrained by it own stiffness ( a factor of the plywood's mechanical properties, the spacing of the sleepers and the attachment mechanism of the plywood to the sleepers).
I am sure that there are other design factors to consider.
A professional structural engineer should be consulted if there are any questions about floor strength and design requirements and how much flexibility you want to end up with. A call to one in the yellow pages can probably get you a lot of answers. Although they may be of the type "you can't do that."
The type of floor discussed here is commonly done, and the XPS has a very high loading before it will deform. The plywood and sleepers will distribute the weight much more evenly across the XPS.
Another note:
If you put XPS in between the sleepers, then the sleepers are really not serving any purpose, other than making installation harder. They are serving no structural importance in this case. Instead of putting XPS between the sleepers, just put the ply down over the XPS.
Tom
If you put XPS in between the sleepers, then the sleepers are really not serving any purpose, other than making installation harder. They are serving no structural importance in this case. Instead of putting XPS between the sleepers, just put the ply down over the XPS.
(smacking forehead) Duh! Absolutely right! Just glue the T&G together like a floating floor. But, wouldn't you need something to keep the plywood from warping? Most 3/4" needs to be nailed down to something, unless it's dry when you get it and stays that way. I suppose you could glue the ply to the XPS.
Now we are starting to describe something like a SIP laid flat, aren't we?"Everything should be made as simple as possible, but no simpler." A. Einstein
http://www.albionworks.net
This thread may about be dead... but i was thinking about something along your lines. If I'm goning to put the ply over the sleepers... why put sleepers in at all. Why not use 3" rigid and then lay 3/4" T&G over that? Then the ply is floating; maybe that is a bad idea.
The floor goes down next week.
-David
The first calculation assumed a uniformly distributed load, but the second considered a concentrated load. In the example it was 250 pound on each leg. Since the leg is sitting on 3/4" plywood the load is distributed over some area. I used an assumed area of 3½ inches square. Though this is an assumption, it's a reasonable and conservative one, I believe. If I imagine a 4 inch by 4 inch square of 3/4" thick plywood resting over a 3½ inch by 3½ inch square hole, and a large person stood in the middle of it, the deflection of the center of the plywood would be so small as to be negligible.
Since that analysis shows the compressive strength of the foam only needs to be 21 psi, and foams are easily available with much higher ratings, I'm comfortable recommending the proposed arrangement as satisfactory.
It's been a while since I read the postings, and I can't remember if someone said this already, but don't forget to put electrical conduit in the floor for an outlet for your table saw if you want to. You'll have to use metal, of course.
There is another option. There is a product called "Dricore"...(http://www.dricore.com/). It is an OSB T&G with a couple of hundred plastic "feet" per sheet that get layed right on the concrete and just "floats", not shot to the floor. Having shot down WAY too many sleepers, this would seem to be a simpler solution. If it were me, I would use it with a layer of 3/4" ply or hardwood strip flooring over it, although the second layer may not be neccesary.
Good Luck,
John
Edited 3/14/2004 6:51 am ET by JMartinsky
There is another product similar to Dricore called Delta-FL. Check out http://www.deltafl.com. It has a compressive strength of 6000 psf which works out to 42 psi. with the 3/4 in ply distributing the load from the machinery that seems adequate.
It has been a while since I got the prices and did the math but the DeltaFL with 3/4 ply on top came out cheaper. That may be because I would want to put another layer of something over the OSB that would stand up to the rough treatment better. Of course, the 3/4 ply was going for about 18.50 a sheet back then.
I would love to hear if anyone has any experience with either of these products cause they would surely be less work to install and it seems they would provide better moisture handling than the sleeper system.
I hope to get started doing my floor in a couple of months.
I'm not familiar with Delta-FL; but I've seen the Dri-Core and it looks like a good product. According to their web site it has an R2 value.
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