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Thread: Shop build, Phase 1, Plywood flooring

  1. #1
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    Shop build, Phase 1, Plywood flooring

    Greetings to all --

    I've got equipment arriving in December, but well in advance of that, I'm putting in some rockwool insulation up and must deal with the floor. Original floor is a thin layer of concrete over stone, circa 1870. I filled in the most egregious areas of the floor with epoxy last year, and will probably do more of that over time.

    Not only is the shop floor uneven, but the 4'x8' sheets of plywood are not flat. My main concern is that it's a trip hazard, and I'm wondering how to best address that.

    All feedback welcomed --

    Thanks,

    Ned


    closerampview.jpgfarrampview.jpgshop1.jpgshop2.jpgshop3.jpg

  2. #2
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    I think you would be better off laying down a vapor barrier and topping that with some sleepers upon which you will fasten the plywood. Level the sleepers to ensure a level floor.

  3. #3
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    I agree with Jim. You can level the sleepers easier than the floor. Yes, you loose a few inches of ceiling height but you have a true surface. Insulate the cavities. Also, should you choose to do $o, you could lay some pex tubing in the cavities and radiant heat the floor.

  4. #4
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    Thanks for the replies -- the equipment that's arriving is between 500 and 1,500 lbs, and given that amount of weight, I didn't think that having any cavities under the plywood would be a good idea. but will consider the recommendations.

  5. #5
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    It would not be that expensive to pour a new floor, it that slab is inside of a foundation. Probably less expensive than a wood floor right now. And it could be level and smooth.

  6. #6
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    Just laying down plywood gives you the worst of everything & won't give a satisfactory floor. Probably worse than you can imagine. If you don't want to pour a new floor, then sleepers with foam of the same thickness between them & 3/4" plywood on top will handle the heavy machinery. You could build up that thickness with another layer of plywood if needed.

  7. #7
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    I'd put in 2x furring over a vapor barrier, shimming things flat/coplaner/levelish, put rigid foam insulation between the furring and then apply the plywood on top, securing it well to the furring. I'd leave the furring "floating" and use some appropriately sized pocket screws to keep the frame together during the process.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  8. #8
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    Thanks everyone --

    For sleepers or furring, any suggestions on the distance between them to handle heavy machinery?

    And Jim - might you be more specific about the 2x? 2x2? 2x4, flat side down?

    thx
    Last edited by Ned Otter; 05-29-2021 at 5:57 PM.

  9. #9
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    Ned,

    My floor is a traditional wood joist construction type. The engineer spec'd 12" on center for the joists and 2 layers of 3/4" plywood running opposing directions. I think it my have been overkill, as even my big cabinet saw never caused any noticeable deflection. If I where doing your floor, I'd lay 2 x 4 sleepers on 12" centers and 1 layer of 3/4" plywood, after the foam between the sleepers.

  10. #10
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    +1
    IMHO, I would either pour a new floor or get some leveling cement. It's going to be a PITA to level an uneven concrete floor with sleepers

  11. #11
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    Hard to tell what he's got at the base of the framing. Right on the cement overlay, or raised a bit?

    So here's my thought about it, and feel free to tell me why it's a bad idea. Because, quite frankly, I'm not so sure it isn't ;-)

    I'd insulate the walls, and put a 1" layer of foam over the whole thing. And then pour another 2 or 3 inches of concrete. The foam would isolate it from the framing. And then sheath with a gap to the slab as a normal build.

    Bad, potentially:

    There's a gap for water to run off the slab and pool around the framing.

    The sheathing doesn't tie into the sole plates. I don't know how much that matters in this case, but you could sheath first, and then run a 4 inch tall foam wall before pouring.

  12. #12
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    I'd probably do 2x3, flat side down, 16" OC. The rigid insulation adds some surprisingly effective intermediate support between the sleepers for the plywood. Unless you are using significantly heavy "old iron" or big Euro gear, you'll be fine. I'm seriously considering doing this for my coming shop build. I have to do a slab for multiple reasons but would love to have a wood floor for comfort. If I can swing the cost, I'll do exactly what I suggested here for my own setup.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  13. #13
    Hi Ned,
    Depending how out of level your existing floor is would determine if you need sleepers on edge or on the flat. If it’s fairly decent you can rip 2x6 (pressure treated) in half and put them flat. I would spring for the foam insulation personally. A couple other small things not mentioned would be;
    -to have sleeper blocking under all the joints along the 8’ plywood edges between the longer 16” centers.
    - use some PL sub-floor adhesive
    - lots of screws vs nails
    - T&G ply is much better than square edge for this
    And for what it’s worth, if you are concerned about 3/4 ply not being stout enough, you could ask about 1-1/8 or 1-1/4” t&g ply at a lumber yard. I sourced some of it about a year ago and had it pressure treated for my roof. Seems crazy but building down here is a bit different. Best of luck!

  14. #14
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    Quote Originally Posted by Jim Becker View Post
    I'd probably do 2x3, flat side down, 16" OC. The rigid insulation adds some surprisingly effective intermediate support between the sleepers for the plywood. Unless you are using significantly heavy "old iron" or big Euro gear, you'll be fine. I'm seriously considering doing this for my coming shop build. I have to do a slab for multiple reasons but would love to have a wood floor for comfort. If I can swing the cost, I'll do exactly what I suggested here for my own setup.
    I would pretty much agree. If you use Owens Corning Foamular 400/600/1000 as your insulation board it will easily handle your 1500 lbs. loads. With a compressive strength of up to 100 psi, the load, distributed to the foam boards via the flooring, even a 25 psi foam board would probably suffice.

    But as a retired energy manager I hate to see you stop at the sleepers. 2x4 sleepers gives you almost 25% r-1+ on your floor negating the benefits of much of the insulation. Consider gluing a thin sheet of foamular on top the sleepers and insulation boards to break the thermal contact between the sleepers and your flooring.
    For your flooring consider gluing and screwing Advantech OSB down instead of plywood. Much stiffer. Moisture resistant. I would not use any other product over a concrete subfloor, even with a vapor barrier.
    You could probably sell your plywood easily on Craigslist. Don't let materials on hand deter you from doing the best job you can. This is a decades long decision.
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  15. #15
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    Back up a step

    Since this is thin old concrete in poor shape presumably without any metal, I would remove it, add rebar, and pour a flat concrete floor. Whether you add a wood floor is up to you. Otherwise you are adding a bandaid to an infected wound.

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