How to replace this plywood floor?

Discussion in 'Flooring' started by farmerjohn1324, Jul 14, 2018.

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  1. Jul 14, 2018 #1

    farmerjohn1324

    farmerjohn1324

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    The old plywood was removed because it was uneven. Possibly something to do with the fact that this house is on brick columns that are about 3' tall. It does not have a concrete slab foundation.

    What needs to be under the plywood (either masonry or bricks) to make it flat and where does it go? How many columns?

    Do I then Tapcon the plywood to the columns? How do I attach the plywood to the rest of the house?
     

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  2. Jul 14, 2018 #2

    farmerjohn1324

    farmerjohn1324

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    I found this picture of when just the plywood was removed. Apparently, there are 2x8's going across concrete blocks.

    When I put this back together, how do I make sure everything will be level and not going to move?
     

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  3. Jul 14, 2018 #3

    nealtw

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    Well that is pretty sad. Under the windows you could use hangers if the building is stable enough.
    Looks like the center beam could go over to the left, I don't much there to tie to.
     
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  4. Jul 14, 2018 #4

    joecaption

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    What I've done dozens of times with these DIY build additions is first really look it all over from the roof down and see if it's even worth fixing.
    Reality sucks, but it makes no since to waste time and money on something that's just going to fail again.
    Often times I'd find the roof had been leaking for years, undersized rafters, not enough roof slope, tied into the house wrong.
    If I was stuck having to just repair what you have there, first thing I would do is remove all those undersized floor joist, and anything else inside the crawl space, then see if there's proper footings and enough of them under those outside walls.
    Check for rotted or insect eaten wood at the bottom of the walls.
    Check for level and flat as best I could to see if the colums had sunk or were failing.
    If all that looked good then I would be cutting a 2 X 10 pressure treated to length to fit along that long wall attached to the inside of the rim joist or beam if that's what you have instead.
    What I do at first is insert three 3" long decking screws into the board before installing 2 on the ends one in the middle.
    I first screw in the middle screw, then cheaking for level I insert the end screws.
    (there's a reason for just tacking this up like I suggest, you will soon see)
    Do the same for the end walls, and last the one along the house wall making sure all the tops of the boards are even in the corners.
    Now I lay out for my floor joist every 16" O/C.
    Once it's laid out you'll now know where you can insert LedgerLok screws without them being in the way of the joist hangers.
    At a minimum I'd be using 2 X 8 PT floor joist.
    Note; I use all PT for the joist because your so close to grade, I'd use 2 X 10's for the rim joist because it's stronger and will help keep those outside walls from sagging.
    I'd be using Advantech, not plywood for the subfloor, any nails or screws used need to be ACQ approved.
    8D, ACQ approved ring shanks work great.
    Advantech comes with the nailing pattern printed right on the panels, do not skimp on nails!
    Make sure to apply constrution adhesive to the tops of the joist for a far stronger and less squecks floor.
    Never have the narrow butt seams line up when laying the subfloor, they need to be offset by at least one joist bay.
    You never want to end up with a really short piece on the end of a run, if it ends up being something like 16" as an example, cut off 16" off the first piece so the end piece will now be 32".
    (You want to make sure all the 2 X 10's you use are as straight as possible)
    Make sure to check the joist for crown and install crown side up.
    Once the joist are in place add blocking down the middle.
     
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  5. Jul 14, 2018 #5

    farmerjohn1324

    farmerjohn1324

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    Advantech = OSB? Is that weaker than plywood?
     
  6. Jul 14, 2018 #6

    joecaption

    joecaption

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    It's stronger, will never delaminate, far more water repellent. comes with a lifetime warranty.
    It may look like OSB but it's a totally different product.
     
  7. Jul 14, 2018 #7

    nealtw

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    Joe missed one detail. on the 16" lay out the first joist is 15 1/4" from the wall. Not counting the one at the wall.
     
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  8. Jul 15, 2018 #8

    joecaption

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    Almost always the last joist is going to come out to be an odd number of inches at the end on a DIY built addition, you do not want to end up having to install hangers in a tight space.
    Going to have to use common since on this one.
    Advantech can span up to 24".
    As poorly as that was built I'm sure it's also out of square which will cause issues when your going to lay the panels, they may not split the joist in the middle.
    Do not waste time trying to cut the panels to fit, faster to just attach a PT 2 X 4 to the side of the joist.
     
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  9. Jul 19, 2018 #9

    farmerjohn1324

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    This is the new floor framing. Does it look sturdy enough. I don't know how to test it.
     

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  10. Jul 19, 2018 #10

    slownsteady

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    How far apart are the joists? can't really tell from the pic.
     
  11. Jul 19, 2018 #11

    farmerjohn1324

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    I think 16". Is that good?
     
  12. Jul 19, 2018 #12

    joecaption

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    Is it pressure treated wood?
    Can not tell if you used joist hangers on not, if not then add them now.
    As I'd mentioned before I'd strongly suggest using Advantech, not plywood.
    Sure looks like that spacing is more than 16" O/C from that picture.
     
  13. Jul 19, 2018 #13

    mabloodhound

    mabloodhound

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    Looks more than 16" to me also. Definitely want to use Advantech with that wide spacing.
     
  14. Jul 19, 2018 #14

    farmerjohn1324

    farmerjohn1324

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    Just measured. It's an average of 22" each. What does this mean?
     
  15. Jul 19, 2018 #15

    mabloodhound

    mabloodhound

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    Then use the Advantech like Joe said it can span 24"OC
     
  16. Jul 19, 2018 #16

    farmerjohn1324

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    Correction: 20" each. Does that change things?
     
  17. Jul 19, 2018 #17

    slownsteady

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    It changes the guy that you're using for framing.:cool:
     
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  18. Jul 19, 2018 #18

    joecaption

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    Good luck now trying to lay the subfloor, none of the butt joints will land on a joist .
    Two of us suggested 16" O/C for several reasons, it makes the floor stronger, and it would be spaced so the subfloor lands in the middle of the joist.
    Left the way it is your stuck having to cut every piece on the short side.
    Look at your tape measure there's different marking every 16 or 24" for a reason.
     
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  19. Jul 20, 2018 #19

    farmerjohn1324

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    I'm not so much worried about the ease of laying the subfloor as I am someone falling through the floor 3 years from now when they're having a party out back in addition to their washer/dryer and water heater.

     
  20. Jul 20, 2018 #20

    Gary

    Gary

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    That looks more like a sink hole under a slab. Sort of like what happened at the corvette museum in Kentucky a few years ago.

     

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