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Community and Q&A

Comfortboard on Interior Ceiling

user-6504396 | Posted in Green Building Techniques on

We are getting ready to put up the interior wallboard.  We have a living room ceiling directly under the master bath above.  The water supply lines and the drainpipe run directly through the living room ceiling space.  We used cast iron for the drain pipe but we are looking for additional ways to cut down on the the noise that will still be there.  I am thinking of attaching 1″ comfortboard to the underside of the floor joists and screwing the wall board directly through that to the floor joists using longer screws.   Can I eliminate the use of furring strips like this or will I get sagging?  The drywall will be 5/8″ thick.  

The other alternative I am considering is to use sound insulation clips and resilient channel and place the Comfortboard between the channels.  This of course would not allow the Comfortboard to run continuously across the area unless I somehow put some spacing behind the clips to provide a 1″ space between the face of the floor joists and the back of the channel.  

The ideal solution will take up the least amount of vertical space and provide the most amount of sound dampening.  

We will also look to wrap insulation around the pipe and pack the cavities with insulation.  I found this study very helpful.

What would be the best solution?

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  1. Expert Member
    Akos | | #1

    Mineral wool boards won't work as it is still pretty squishy. You'll have a hard time getting the drywall seams to line up and not crack. It also won't do much for sound in this case.

    Hat channel and clips works very well for this. You don't need the insulation continuous everywhere, as long as there is some in the cavity it will work to absorb sound.

    If it is available in your area Sonopan is also a good option. Takes up a bit less height than clips+hat.

    Getting some rubber mounts for the pipes will also help as it keeps the noise out of the structure.

    1. AJ__ | | #2

      What's your experience with Sonopan?

      1. Expert Member
        Akos | | #4

        I've used it before around bathrooms. Works better than resilient channel as you can still mount things to the wall afterwards. Sound wise, subjectively, it does about the same as RC.

        1. user-6504396 | | #5

          Do you attach the drywall directly to the Sonopan material or do you have to anchor through it to the 2x material behind it?

  2. gozags | | #3

    You will have the sound of the actions from the pipes - water flowing. You’ll also have the resonating from the action moving through the pipes and where they attach to joists, 2x, etc.

    Is it just single waste line (cast you said) and then some H/C pex for water?

    I had a bunch of pex and then a main waste line adjacent to a bedroom in a basement and fretted a bit because when it was open, it was noisy and obvs, a toilet flush sounds like a toilet flush and that ain’t fun.

    Waste was ABS so got some knock off dynamat from Amazon and just wrapped and cut strips and applied that on the waste, not even doing a perfect job - just sections. That changed the sound there a ton.
    On the pex, I did the denser foam insulators from
    HD and that helped.

    Then I just packed the area with regular Roxul. Then 1/2 wallboard.

    You really can’t hear anything.

  3. user-6504396 | | #6

    Thanks for the reply. It's actually two lines coming over from 1) the sinks/toilet and 2) from the shower/tub to meet in a common line. The two lines run over the great room and the common line runs down the hall. There is no wall in between.

    I'll get the rubber mounts and I was thinking of using Audioseal to wrap the pipes. I have heard good and bad about the channels depending on the frequency of the sound and the resonance of the assembly. Stuffing the cavities with Rockwool will probably do a lot. The bottom of the drain pipe is pretty close to the bottom of the floor joists which is why I was thinking it would be good to get a layer in between the sheetrock and the bottom of the joists.

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