I have pulled up carpet in a home I recently purchased, finding white oak 2" wide hardwood. In the dining room, the sub floor and subsequently the hardwood waves over the floor joists. Between the joists, the subfloor sinks 0.25 in. In my opinion the 0.25 in is noticeable. The subfloor is not 4x8 tongue and groove ply, it is plank sub-floor. How would I go about making this level? I have used self leveling cement in the past on a slab, but considering this is plank sub-floor, I cannot use this method.

The floor joists are 2x10 16" on center.


  • You ask about replacing sub floor or cover with with ply. Are you implying that you are planning to first remove the white oak flooring? – Michael Karas Mar 27 '17 at 13:09
  • I want like to keep the flooring. It is only a 0.25" "wave" but it feels noticeable. I would replace if need be. – Geoff Lentsch Mar 27 '17 at 13:26
  • I understand that the quarter inch wave is noticeable - I would certainly find it so too. You have not really clarified the question I asked. You do realize that in order to change or add to the sub-floor that it is first necessary to remove the oak flooring. Once you get the subfloor flat you would have to evaluate the oak material for possible re-use - which seems doubtful that it would be suitable. – Michael Karas Mar 27 '17 at 13:32
  • You should evaluate also the spacing of the underlying floor joists. On an old construction house there is a possibility that the spacing was way too wide for the types of sub-floor and flooring material. This detail should be in your question to get the better feedback. – Michael Karas Mar 27 '17 at 13:36
  • Yes I do realize that I would need to remove the existing oak. I will add such information this evening. I have access to the floor joists from the basement. There is also gaps between the plank sub-floor, making self leveling concrete out of the question. – Geoff Lentsch Mar 27 '17 at 13:59

I would address whatever caused the subfloor to sag that much in the first place. OSB decking in a humid area will have all sorts of problems, especially crawlspaces with backed fiberglass pinned up against them. All wood, even engineered woods like OSB and plywood, lose a lot of strength when they've swelled up due to moisture issues.

I had a similar situation this last year and was able to address it by using well-placed screws from below. That was 5" wide T&G, though. obviously you're flying blind from below, so you have to guess where the center of the boards are. With hardwoods (and especially narrow 2" seasoned white oak) I would fear splitting the board if you were either too close to the edge or end. Oh yeah - and this job is awful to do while in a crawlspace. I mean awful awful. Like "I am never doing this again IF I survive this ordeal" type of awful.

I didn't finish one room, so it still squeaks when you walk over it. However, that squeak doesn't seem to bother me nearly as much as it did before I decided it was a good idea to take 5 years off of my life by doing that type of work in that inhospitable location.

  • I understand the original cause of the issue should be resolved. I believe it was moisture. Below this room there is an unfinished basement, with poor grading against the wall. I am going to fix the grading, and may need a dehumidifier, though it does not resolve the waving sub-floor. – Geoff Lentsch Mar 29 '17 at 19:26
  • I have been remodeling for 15-20 years now professionally, and I would leave it alone entirely.... or be prepared to remove and re-deck the entire subfloor area. You could, in theory, use self-leveling cement to help , or add furring strips to the low areas... but this is extremely time consuming and tedious. If you're the type of person that can't deal with the wavy floors, you're probably the type of person that wants to do the job right... and that means replacing the subfloor with Advantech (gold standard for new construction) or true plywood. – Benjamin Lane Mar 29 '17 at 21:03

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