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Community and Q&A

Spray Foam Insulation for Soundproofing

josephny | Posted in General Questions on

I’m making lots of progress (hopefully in the right direction) on the gut rehab of my 4500 sq ft 3 story house.  Envelope will all be closed cell spray foam (walls, roof rafters, basement walls).

Now I’m wondering about insulation in the interior walls and between floors.

I was all set on not insulating between floors to allow for air and heat energy to flow (which I understand is quite complicated and not necessarily a desired thing).

Then my wife and I were talking about keeping sound/noise from transferring between floors and between interior walls.

I’m wondering what everyone here thinks about open cell spray foam between floor joists (between floors 1 & 2 and floors 2 & 3) to keep the noise down, and/or in the wood 2×4 interior walls?

I understand enough (albeit very little) to know that OC SF between wall studs won’t be a super-duper effective noise control, but from what I read it would be a huge improvement over nothing in the wall as well as a huge improvement over simply double sheetrocking and/or fiberglass batting (right?)

I’ve 99% sure I’m going with an LG heat pump with separate air handlers for each floor and all tied into a central ERV.


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  1. Expert Member
    BILL WICHERS | | #1

    There is no point to putting spray foam in any interior walls or floors that have conditioned space on both sides. Spray foam is not commonly used as a soundproofing material, either.

    If you want to keep sound down between rooms, the easiest two things you can do are to use 5/8" drywall instead of the more common (in residential construction) 1/2", and put sound control mineral wool (which is a bit thinner than the "regular" stuff) in the stud cavities. If you don't want to spend the money for mineral wool, fiberglass works too but is a little less effective. Either type of insulation is likely to perform at least as well as spray foam, and I'd expect the mineral wool to perform better.

    If you want sound control between floors, it can be more complicated. About the best you can do is a double layer of 5/8" on the ceiling of the lower level, and suspend that from hat channel. That's going to add a good amount of cost to your build though. After that, fill the joist cavities with mineral wool batts (best), or fiberglass batts (next best). Most of the "work" is done by the drywall and hat channel, which will be far superior to just filling things with spray foam.

    It's not common practice to insulate interior spaces for thermal reasons unless you have a seasonal room or something like that. I wouldn't bother trying to thermally insulate interior rooms from each other.


  2. user-5454807 | | #2

    Agree with the above. Mineral wool also has the added benefit of fire resistance (melting point above 2000 degrees F - zero flame spread and smoke development) and filling cavities with it can therefore slow flame spread in the case of a fire.

  3. josephny | | #3

    This is really great information!

    I was planning to use 5/8" sheetrocks screwed directly to the floor joists, but using hat channel to affix the sheetrock with mineral wool between the joists sounds like a great solution.

    And using mineral wool between the wall studs sounds like a great solution also. I initially moved away from that because the articles I read seemed to indicate that 5/8 sheetrock with mineral wool between studs was not as effective at blocking sounds as spray foam.


    1. Expert Member
      Akos | | #5

      You want RC channel, not hat channel. You can use hat channel with isolation clips as suggested bellow, but they tend to be spendy.

      Generally for single family residential, 5/8 directly attached to the joists plus a layer of safeNsound is good enough. I would only do more for something like a home theater room.

  4. user-5454807 | | #4

    Also spray foams can give off toxic gases in a fire.
    There are sound absorbing clips that can be used with hat channel to further reduce sound transmission.

  5. josephny | | #6

    Ah, Resilient Channel (not hat) -- got it, thanks.

    Clips for RC?

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