As part of our kitchen renovation, the contractor is extending our hardwood floor. As you can see in this photo, they have cut out boards from the old floor and are adding new boards. I think this is called "toothing". It looks like they are not putting underlayment under the new boards that join with old boards. What you cannot see in this photo is that we have a basement below.

Picture of floor

It seems to me that either the underlayment is necessary between the hardwood floor and the plywood subfloor, in which case it must be under all boards, or it is unnecessary, in which case they are wasting time and money. It seems that being inconsistent could cause bowing or warping.

So, my questions are:

  • Should the contractor be putting strips of underlayment under the new boards that join with old boards?
  • Given that this is the floor for a kitchen, where liquids may spill, does that change the importance of the underlayment or of being consistent with underlayment?
  • Being on a wood base it may not matter I do use underlayment and would think if some sections do not have it that will cause loose areas, other than that it looks like they are doing it directly.
    – Ed Beal
    Feb 3, 2018 at 17:08
  • Why not put this into an answer I can vote up or accept, instead of a comment?
    – Jim L.
    Feb 4, 2018 at 0:30

2 Answers 2


I have seen glue down floors with no paper, it was a wider board, but still solid flooring, not engineered. When I was coming up in the trade when I was in my 20's I was told paper was used as a cushion, I thinks it was wrong. When nail down wood floors move as with a cushion under it, they squeak.

The paper is used to prevent I think, and you may find elsewhere, to prevent the mass migration of moisture from below to the flooring above, and perhaps to keep spills from going through below. Moisture going through a floor is inevitable and necessary. The rapid transfer is harmful and will damage the floor. The paper slows the transfer down. The floor finish and cleaning up spills asap is part of that.

Where the paper is missing at the joints can only be repaired to a degree, the driving of the new floor will have a tendency to rip the strips up as it is being driven in if they are narrow. Narrow strips will have many joints anyway so in the long narrow areas it may be a moot point. I think some areas may have been able to have been detailed better, like sliding the paper up under some of the ends to cover a little better, but if the action doing this loosens up the existing, then it is better not to do so for creating squeaks.

IMO, they are doing an somewhat acceptable job on the paper, their toothing is excellent, tying in new to old and finishing it usually stands out a bit, but spreading out the toothing long into the old floor helps blend it in. The ends of the flooring where they are driving it in, leaves a little to be desired, I see the ends are getting dinged up from the hammer by not using an effective drive block to protect the new floor while being driven.

  • I need to add, I see they are using #15 felt paper on the floor. I see it is labeled as floor underlayment I may be wrong, but this is a lot thicker that the usual stuff. #5 is what is normally used. In MD where I am from, it is referred to that. In WA state where I am now I see it refereed to as 60 minute. Still learning.....
    – Jack
    Feb 3, 2018 at 17:19
  • The answers to my two bullets remain unclear to me. Could you please add a couple of sentences that require fewer inferences?
    – Jim L.
    Feb 4, 2018 at 0:29
  • 1
    First point, the strips are not critical in the narrow areas. Second point, cleaning up spills and the finish coat on the floor is the main line of defense from liquids on the surface. Paper or even bare plywood will allow the liquids to stop and set under the floor. The underlayment is to mitigate the mass migration of moisture or humidity from under the floor, for example a crawlspace or basement.
    – Jack
    Feb 4, 2018 at 1:29

is it a finished basement or dirt crawl space, thats the thing that needs to be known. the way he is lacing it in is fine, most do it that way. the 15 pound felt is industry standard and is abolutely fine. if you have a dirt crawl space then maybe id worry about moisture, but if its just basement no big deal. also i glue those in with face nails after that, stick much better then it would to the felt.

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