I am installing laminate flooring in my 2nd story and have come across this in a hallway. The floors otherwise are pretty level, but there is a bad hump where these two pieces of plywood meet. About 1/4" if I hold the level at the center of the two joints on each side.

Any thoughts on how I can fix it? I thought about using a planer on the high point to bring it down.

level showing the gap between two uneven pieces of OSB subfloor

Close up of the level showing the distance to the floor (but without a direct indication of distance).

  • 1/4" is not a small difference to sand it down to make a smooth transition. How about lay another layer of board (extends to the walls) to make up the difference.
    – r13
    Sep 6 at 19:48
  • I thought about that, but even a super thin board might cause more headache for the rest of the upstairs. The room the issue is in is a square hallways that connects to the entire upstairs so I would have to continue that board I think for the rest of the upstairs. Or have a transition in all 5 doorways to this hall.
    – Atcdiy
    Sep 6 at 20:28
  • Depending on where is the butt joint, you can terminate the board at the doors that separate the rooms to the hallway or make the hallway like a raised island.
    – r13
    Sep 6 at 20:39
  • Your level shows the gap, but it doesn't show which of the two pieces of flooring are out of level. Is either piece of OSB actually level, or do they rise up in the middle because the joist below is a bit too tall?
    – FreeMan
    Sep 7 at 12:56
  • Does it seem like that's swelling due to moisture during construction, or does it seem like a joist is high? (In either case, another layer is not the solution. That causes more problems than it solves.)
    – isherwood
    Sep 7 at 13:07

Thank you all very much for the advice. I decided to give the planer a go, since worst case scenario, I could rip the subfloor out if I made it worse. It worked REALLY well. I was able to completely get the peak out of the floor, sanded it, and now its level! I think had this been a bigger area, taking it out would have been a better plan, but with there being a lot of gas and electrical I was nervous.

  • Please don't add "thank you" as an answer. Instead, accept the answer that you found most helpful. - From Review
    – FreeMan
    Sep 9 at 14:57
  • Neither answer was what solved this. The planer was the answer
    – Atcdiy
    Sep 9 at 15:33

That's OSB flooring. You're not going to be able to plane it down. The planer will, most likely, just pull the chunks out of the board leaving a mess.

As bad as that missing chunk is closest to the camera in the first picture, I'd suggest that you cut out at least some of that board and completely replace it. This will also give you the opportunity to level the new board with the rest of the floor.

  • You seem to be implying that there's swelling due to moisture. I'm not so sure. If so, a belt sander is the solution. If not, planing of the joist is the solution.
    – isherwood
    Sep 7 at 13:06
  • Not necessarily, @isherwood, I kept looking at the pics looking for that, but I don't see it. That broken up piece of OSB does look like there's another chunk that's ready to break out, though. One high joist was my thought (hence my question on the OP asking if either piece is actually level). If flooring is removed from both sides, then yes, that high joist can be planed/sanded down until it's flush, then a new piece of flooring added to replace it.
    – FreeMan
    Sep 7 at 13:25
  • Thanks for the comments. I agree I think it's the joist. I was actually able to take a planer and take the "peak" at the joint of the boards. The rest of the room is level (or very close to it)
    – Atcdiy
    Sep 8 at 19:48

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