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I came over here from reddit because I really want some feedback on this idea I stole from another redditor (they haven't responded to my inquiries, but I really like the idea).

I'm currently planning to finish my basement. The first major hurdle is leveling the concrete floor. I've looked into self leveling concrete, but ruled that out due to the volume, effort, and significant cost involved in going that route.

That leads me to sleeper floors. My floor is very uneven. This isn't due to heaving or cracking, it honestly just looks like a bad pour since the surface of the concrete itself isn't even all that smooth. Rip cutting a bunch of sleepers that would sit level over all the undulations seems like a chore.

Another poster a few months back mentioned using 3" pvc pipe cut into rings of various thickness and glued to the floor in a large grid pattern worked well as sleepers. This sounds like it would be easy: set up the laser level, set the end of the pipe on the floor, mark and cut the pvc at the laser intersect, glue it down, move a foot or so over and repeat. Then lay osb over the grid.

Somebody tell me why this is a bad idea? What am I missing?

TL;DR, can I use PVC rings of varying thickness as leveling sleepers directly under OSB subfloor in a finished basement?

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  • I've seen this method used on concrete paver patios on multistory condo buildings, worked excellent.
    – matt.
    Dec 16, 2023 at 4:51
  • I wouldn't do it but I can't see anything wrong with it. Dec 16, 2023 at 5:07
  • Thank you both. Rohit, I hear you. It sounds like such a redneck idea, but I just can't think of a reason not to. Matt, I've actually seen a product specifically made for that application (they're basically telescopic pedestals), but they're a bit too thick for my application. But the concept is the same, which makes me think it should be viable. It's not like I'm going to be throwing 1000's of lbs. on this floor either. Dec 16, 2023 at 5:34
  • There are plenty of fine solutions to raising a level basement floor. All of them require a tireless eye for detail, careful precision, and tedious tweaks to get it right. Even the slightest belly or bow will cause the OSB to rock back and forth mercilessly. I hope your flooring choice will handle deflection well.
    – AdamO
    Dec 16, 2023 at 6:29
  • Popham, that is the type of analytical breakdown I was hoping for. Do you think the 12" grid is overkill and I could possibly get away with 16"? Thank you for the breakdown! Thank you for the reply AdamO, it will be carpet throughout. The plan is to anchor the OSB the osb with some longer Tapcons to reach the concrete with plenty of bite. Hopefully that minimizes some of the movement. Dec 16, 2023 at 13:34

2 Answers 2

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From the AWC's 2018 Manual for Engineered Wood Construction, OSB's panel shear through-the-thickness strength increases from a minimum value of 155#/in (for 24/0 OSB). Based on your 3" PVC diameter, that's (155#/in)(3.14)(3in) = 1460# punching shear strength, where that's plenty on a 12" grid.

Since the OSB won't have the full joist supports running perpendicular to its strength axis, getting sufficient stiffness and strength out of the OSB sounds analytically tricky. Given your 12" grid, where the 3" PVC implies 9" spans, a */16 span rating intuitively sounds like plenty.

If you want to use fewer PVC stubs, then I would abandon the square grid for a rectangular grid. OSB has a strength axis that makes it substantially stronger when supported on lines running parallel to its short edge. Look at the OSB panel stiffness values from page 52 of the document linked above, where the stiffness in the weak direction is about 1/6 the stiffness in the strong direction. Your grid should simulate as best as possible lines of support running parallel to the short edge of the OSB panels. Standard span ratings are 16" and 24", so those are good spacings for the lines. Along each line, I would put PVC stubs on 9" centers. For the 16" lines you would want */16 rated OSB. For 24" lines you would want */24 rated OSB.

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A person who was skilled and experienced in the use of floor leveler could probably get this floor level in short order. The idea of using these PVC rings is interesting to think about but could led to a failed installation.

In Dallas TX some "gotta have real hardwood types" have thick tongue and groove plywood nailed (concrete nails?) to a grade level slab foundation as a nailing subfloor for real hardwood flooring. Yikes! Would an OSB subfloor directly on concrete perform properly in a basement in a cold wet climate?

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