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

I just bought a condo in an old building. The ceiling is plaster and is not in good shape. The contractor I spoke to said the best and least expensive thing to do is to just place blueboard over the existing plaster. Does that sound right? Thanks.