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Hollow-Sounding Floor

user-6900238 | Posted in General Questions on

I’ve begun laying my flooring down, albeit just in the bathroom at this point and I’m not sure the hollow sound is acceptable. Here’s the situation…

Slab on grade(dry enough), then CDX sleepers fastened to the concrete 16 OC, then rigid foam in-between sleepers, then the 3/4 fir nailed down. There is only a negligible difference in height between the foam and sleepers.

Does anyone know of a way to use this system and not have the hollow sound with every step? I’m sure part of it is the empty room, ┬ábut not all.

I wonder if a layer of Felt may be useful. I was planning on it anyway, for squeaks.

I could skip the foam all together and lay full sheets of plywood down. The foam isn’t really adding that much insulation and the floor isn’t crazy cold ┬ábut I already have the foam and not that quantity of ply… I could also use foam around the perimeter then ply in the field..Hummm?

Has anyone had success with another method?



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  1. Steve Knapp CZ 3A Georgia | | #1

    What is your flooring material? I'd be concerned about the height difference with tile.

  2. user-6900238 | | #2

    No tile, hardwood throughout.

  3. Roger Berry | | #3

    Your description of CDX sleepers - then nailed down 3/4 fir is a bit puzzling. 3/4" fir plywood, then flooring? Or 3/4 fir strip flooring direct? How thick is the CDX? If not at least 3/4, the nails you are setting may actually be causing the CDX sleepers to pop off the floor between fasteners. (I am assuming concrete fasteners for the CDX.) If you are applying strip flooring direct to the CDX the format may also play into the sound problem.

    I have found that engineered hardwood floors composed in wide plank format to be what I call "tap dancey". Strip flooring of full thickness hardwood have a different sound to them. Is the flooring a full naildown or a snap lock type? The sound deadening felts and foams do have different properties, but going over even a dry cement floor would make me choose the foam type first. The Pergo brand foam seems to be a better quality than some, but I my current floors have the foam integrated onto the stock. I don't make sound when walking, but the dog's toe nails sure do. Of course, that is why we have Pergo - the dogs toe nails.

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