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I plan to float a bamboo floor over top of our kitchen's existing linoleum (or vinyl, not really sure which). The problem is that the floor has a couple of high joists that make it pretty uneven along the width of the room. The height difference reaches half an inch in the worst spot. How can I smooth out the floor?

Floor details: The kitchen sits above a partially unfinished basement (meaning we have access to some of the problem joists). The subfloor* is 3/4" OSB. On top of that is the "linoleum", which is backed by wood so that it's about 1/4" in total thickness.

** Room details:** The room is a U-shape about 18' wide that opens to the rest of the house after a length of 20'. The cabinets line the "curve" of the U, with the bad joists cutting "across" the U, just past where the cabinets end. At one end of the bad joists, there is a sliding door that we intend to replace.

Other concerns:
We installed the cabinets on top of a 1/2" spacer (to fit the bamboo) directly on top of the floor, and adjusting those is more or less not an option. So while we aren't opposed to cutting into the linoleum if necessary, we will need to match its height somehow so that the cabinets are at the appropriate height.

There's a cabinet about 20" from the worst joist, which is also where two OSB boards meet. So we can't remove the entire board, but we could potentially cut it back to the previous joist and path that spot somehow. I'm not sure if there are structural issues to worry about here.

One thought we had was to cut out a wide strip of the linoleum along the bad joists, then fill the now-pits to level with the rest of the floor. Self-leveling products sound handy, but my research tells me that there aren't any that work properly on OSB. Plus, I'm not sure if that even makes sense for use in a narrow strip like that. Some sort of thicker, manually-leveled putty also makes sense, but I don't know if anything would work for that purpose.

So I have a good understanding of where the problem areas are and what the result should look like. What I'm looking for is: what combination of steps can we take to level the floor, while keeping the cabinets where they are, the subfloor stable, and not raising or lowing the overall floor height?

*As a side note, we have a spot where we cut out the linoleum to get to a spot where the subfloor has some wood rot. We intend to patch the subfloor here, and so I'd like to handle that in a compatible manner. If you have any insight here, I'd love to here that as well.

  • any way you can give us some pics so I can see the extent of the deflections? – shirlock homes Jul 27 '16 at 21:19
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I have read your question several times and feel there is no simple solution to the problem. Laying any kind of wood floor over an uneven base floor can be difficult with disappointing results. This is especially true with thinner laminates or veneer type floating floors. Seems can buckle or open and the floor can have a hollow feel.

It is much easier to fill low spots than lower a high spot. You said in your question that the difference is about 1/2 inch. That is a large difference to bridge. Usually the best way to eliminate a high spot is to raise the level of the rest of the floor to the highest level. Cutting down the joist is not a solution unless you are willing to remove the subfloor. You did not say how large the entire room is or how it transitions into other rooms or doorways. That information would be helpful to know. The fact that you installed cabinets before solving the floor issue complicates the fix.

The first step is to map the floor by using a long true straight edge and or a laser to visualize the contour of the existing floor. This will tell you what areas need to be raised and by how much. The differences will vary over the span of the room. Since wood flooring can bridge small gaps, creating a perfectly smooth base is not necessary. The goal would be to create a level plane so the new floor will lay flat. The fillers or shimming can be done with thin plywood, luan, scrap vinyl, leveling compound or a combination of materials. Baseboards need to be removed and reinstalled after the new flooring is installed. This process can be tedious and time consuming, but if done well, will result in a much better finish product. It really doesn't matter what the subfloor fix looks like as long is it leaves a flat surface. Your new floor will cover all that.

  • I edited my question to be a little clearer. I have a good idea of where the floor is out of level, but don't know how to level it given the specific constraints. – TheRubberDuck Jul 27 '16 at 13:51
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Moving the cabinets really sounds like the best option (even though I heard you say it's not).

If space allowed, I would consider using 2x4's on side (kind of like furring strips), which might be easier to make level than the whole floor; then you would lay new subflooring (3/4"). So the total height added would be about 2.25". While you're at it, it would be an opportunity to consider a hydronic heating system.

Edit- to thoroughly exhaust alternatives, you could also rip out the old floor and sister 2x4s to the joists to make them level. This would be slightly more expensive if you have to dump the old floor, and if the joists are 24" apart, then you need 7/8" plywood or 1" OSB.

  • I'm having trouble following. Where would I place these 2x4s? "New subflooring" makes me think the old will be removed; would the 2x4s go on top of the joists, or attached to the sides to widen/raise the joist area? Or is all of this going on top of the old subfloor and truly rasing the entire floor over 2"? That seems very extreme, and like maybe we could use a thinner board. – TheRubberDuck Jul 27 '16 at 14:09
  • @EnvisionAndDevelop 2x4s placed over what you have now... the old floor (which is 1/2" off level). You could lay 2x4s along the joists, or I would run them across joists (are joists 16" or 24"?). Leveling the 2x4s with shims should be easy. You could perhaps use something like 1x3... which means +1.75" but this wouldn't change moving the cabinets (the extremeness is moving the cabinets, yes?). Since 1x3s are thin, you need more shims. As for new 3/4" subfloor on top, that's kind of non-negotiable for 16" spacing between the "furring" strips. If using 2' spacing you need 7/8" plywood or 1" OSB. – Ben Welborn Jul 27 '16 at 14:36
  • @EnvisionAndDevelop I totally understand why you wouldn't take this option. It's more expensive and labor intensive than cobbling the old floor. Or if you rip out the old floor, then you could sister 2x4s to the joists to make it level and preserve (most) of the height. There are 3 variables and basically 3 options. Varibles: labor, expense, and quality. Options: 1) rip out and dump the old floor and sister the joists; or 2) raise the cabinets and lay a new floor; or 3) use patch, filler, shims, and basically cobble the old floor. – Ben Welborn Jul 27 '16 at 14:52
  • I suppose my question amounts to: How can I try option 3 without moving cabinets (which partially restricts ability to move the subfloor, but not exactly in the problem areas) and keeping in mind that apparently many filler products don't recommend use on OSB. – TheRubberDuck Jul 27 '16 at 15:10
  • @EnvisionAndDevelop I understand why you will not go with the options that I suggested (and I knew that from the beginning, honestly)... but sometimes it helps to galvanize one's ideas to consider all other options. Obviously, patching is inferior in quality... but please don't take that personally. Your comment about self-leveling products is right on, but it's not restricted to OSB. You need a solid floor for patch to work well; concrete floors are better for leveling patch. If the floor sags or moves when you walk on it, the patch will fail (but not before you get paid). – Ben Welborn Jul 27 '16 at 15:24

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