I am remodeling an upstairs bathroom and have removed the old floor. The subfloor is 2x6 planks between the joists. They are nailed into 2x4s that are sistered to the side of the joists. Has anybody seen this type of subfloor before or know what it’s called?

I plan to lay plywood, cement board then tile but some of these planks are sticking above the joists so I would like to just pull them up to have a level surface to work with. The outside planks go under the walls but seem to be loose and resting against the joist that runs under the wall so I don’t believe they are holding any weight. Do these planks serve any purpose? Am I weakening the floor by removing all of these?

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  • Is that 24" spacing between the joists? If there aren't many high spots, you could easily knock them down with a power plane and not have to mess around much more. Jul 14 '21 at 3:20
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    A planer (either remove individual boards that are high and run through a stationary planer, or use a portable planer) will remove the high spots. However, those boards are very dirty and any little bits of anything stuck in the wood could destroy a set of (expensive) planer blades. A belt sander would also do to knock down high spots. If there are a lot and it's really uneven, you could rent a floor sander, but that would probably be overkill.
    – FreeMan
    Jul 14 '21 at 12:21
  • It’s 20” OC. Planing is an option but some of these are loose and squeaky so I would prefer to just get rid of them and prevent any squeaks down the road. The tongue and groove planks that are under the wall are on top of the next joist so I believe that is what’s carrying the weight of the wall. I am thinking these planks between the joists don’t serve a purpose other than acting as the subfloor which I would replace with plywood on top of the joists.
    – Khill
    Jul 14 '21 at 12:28
  • I have never seen that done before, possibly to keep from having a height difference in the bathroom 20” OC spacing is also unusual I can’t see a real advantage to having them.
    – Ed Beal
    Jul 14 '21 at 13:45
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    My opinion is that you're good to remove any of these that are in your way, since they aren't acting as blocking or holding up walls. Given tile, I'd go with at least 3/4 ply, and maybe consider 1-1/8 if the joists are bouncy. Jul 15 '21 at 13:51

Assuming each board is fastened to the joist below (not simply resting unattached), they do add rigidity to the floor to resist shear forces in the event of an earthquake. However, if you are creating your new subfloor with 3/4-inch plywood, that will likely be an improvement over what you have now.

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