I am planning to renovate a bedroom into a multi use room next to a master bedroom and would like to sound proof the common wall. I determined to use Green glue and a second layer of 5/8"th sheetrock on the common wall. My question has to do with a "shared cold air return. Right now there is one cold air return between both rooms in the same Joist space, infact if the lights are on in one room and the other is dark you can see light from the other bed room. How to fix this is my question .

My simple idea is to open the wall at the joist run, and the next joist space, floor to ceiling. cut out approximatly one foot of the bottom of the common joist to enable air flow to the next joist space. Insert 5 or 6 latteral baffels made of homosote, perhaps 2.5 inche deep and the width of the joist space. do this in each joist space just below the vent in the relative walls. Close it up and apply a second layer of sheetrock. Due to various room constructions I can not simply remove the wall , construct decoupled studs and re build the wall. I need to simply double layer the wall and use green glue or quiet glue or supress adhesive. any suggestions on the cold air return. Better ideas? any comments appreciated.

best
Broomast

 

Welcome to the forums

Soundproofing is next to impossible but reducing sound transmission can be achieved.

What do you have planned for the room which makes reducing the sound necessary?

 

Hi Mitch 17,
thanks for your response.

My son has moved out of the room and I plan to make it more of a multi use room. Watch TV, sewing, reading, and perhaps a guest room. Presently you can almost hear the other person breathing in the next room. I want to do as much sound reducation as possible with out going overboard. So I can easily fill the existing joist spaces ( common wall) with blown in Cellulous and put up an additional layer of drywall with Green glue. I do not want to "wast" this effort if it is almost impossible to reduce the sound between the two rooms if I can not do something about the common cold air return. I do not expect miricles but if I could achieve signifiant reductions in sound transmission between the two rooms that would be great. So I can watch Television at a low level and my wife could go to sleep in the next room. creating a separate joist bay for cold air returen in each room and attempting to use 4 or 5 homasote board baffels in each joist bay was my best idea. wonder if other have other ideas about easy ways to deal with the "common cold air return" between the two rooms.

best
Brooks M.

 

Do you have access to the area where the return exits the floor and enters the return plenum? If so, it would be better to move over one or two joist bays and cut in a new return. Doing as you suggest and make the return common, only one bay over won't reduce the sound from the other room, only move it over a little. A separate return for that room would help. If true sound reduction is your goal, don't add sheetrock. Solid surfaces against solid surfaces only transmit the same sound. Cut appropriately sized holes for an insulation blower (rent from home store) 3" below the ceiling in each stud bay and blow in insulation along the offending wall. Patch the holes and finish.

 

Thanks for the suggestions Chandler,

I can access the floor where the "sleeper" is in the wall , but the configuration of floor joists is such that I can not access a "different" rout for the cold air return. I suppose I am "stuck" with attempting to simply move the cold air return in one room over a few joist bays and attempt to includ some baffel system.
I note you suggest it may be a wast of time to double up the drywall. I do inted to use "green glue" between the second layer. Is your experience that this is a wast of effort and money? considering the situation with the common cold air retuern I wondered if it might be.

thanks Brooks

 

Two solid surfaces fastened solidly to each other provide little if any "sound proofing"> Once vibrations are set off, they will travel until they hit a void or soft material. I would hate to have you apply more solid material just to find the "sound proofing" you desired isn't there.

 

More mass between the source of the sound and the area where reduction is desired can make a difference but, as I said earlier, I don't expect you to be able to make the sound go away without significant effort.

 

Mitch and Chandler

Thank you for your comments. I have understood from research on the internet that the use of "Greenglue" with appropriate sound retarding techniques such as insulation in the joist space, use of acoustic cauking a voids and sound deadening material around duplex electrical outlets can reduce sound between rooms between 5 to 10 decibles or at least significant in term of the STC measure, in the reasonable "voice" sound spectrum. This would be just one extra layer of sheetrock on one wall using Greenglue.

Do you have experience with "green glue" between sheetrock or I guess you call it Drywall ( I am over 60 and sheetrock is what it use to be called when the sheets were smaller and it first came out as a replacement for plaster)

 

No experience, never heard of it.