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Residential sound insulation between floors.

KevinKeegan | Posted in GBA Pro Help on

Very Old house wood framed. My question has to do with residential sound transmission between floors. I have access to the joist bays for the second floor floor and second floor ceiling. I do not want to remove the first floor ceiling and can not add another layer of sheet rock over existing first floor ceiling. I was told by an acoustical Engineer that it does not matter what insulation I use, be it fiberglass, cellulose or rockwool they will all provide roughly the same STC as long as the cavity is filled. He also said that if I install a product called regupol which is a type of rubber under the finished floor over the subfloor that will help reduce the impact sound. He explained that unless I can separate the connections between walls and floor/ceilings, the sound will still carry into the spaces you do not want it to go. So given that I’m try to do the next best thing. I would like your advice about the type of insulation I should add to my open joist bays for limiting sound transmission. I plan to insulate all the band joists with closed cell spray foam and all my walls are currently insulated with fiberglass.
Thank you, Kevin

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  1. Expert Member
    Zephyr7 | | #1

    I seem to recall you recently asked almost this same question? I did a quick check and didn't see it though...

    Anyway, your sound engineer is basically correct about the type of insulation -- they all perform pretty similar. Higher MASS insulation will work best, which would mean mineral wool or at least high-density fiberglass compared to the regular stuff. The difference is pretty minimal though. You'd get much better results with decoupling using hat channel, or adding additional drywall, but insulating the joist bays does help.

    Something with some squish to it does help with impact sound. I'm not familiar with Regupol, but I have used Homasote board, which is a dense fiberous material intended for this sort of thing. I've also used an underlayment material made by Cali Bamboo that is essentially 1/8" thick polyiso, which also provides a bit of sound reduction for impact sounds. Either works, just don't expect miracles here.

    Bill

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