My client owns a condo project with sound isolation problems in the party walls between occupied units. The new buyers are complaining of sound eminating from adjacent units. The existing walls consist of a single 2×6 bottom plate, 2×4 studs at 16″ o.c. staggered spacing at 8″ o.c., sound batt insulation woven in between, one layer 5/8″ GWB (probably Type “X”) each side. Sound batts are also installed in the floor cavities below the party walls in these two story buildings. The neighboring wall outlets are staggered in the stud spacing and are fire caulked into the GWB. The Gypsum Association GA File No. 3380 rates this assembly at 40-44 STC (sound transmission class) without the sound batts. With the sound batts, the wall should rate somewhere in the +50 STC range. The Building Code at the time of construction allowed 45 STC for air-borne sound isolation, and 45 IIC (impact insulation class) for impact insulation. Current Code requires 50 STC and 50 IIC. The owner is looking for any additional cost-effective retrofit solutions for sound insulation. Foam insulation is not an option because it would solidify the wall so as to of create a drum head effect with of the walls. Additional insulation (blown) in the walls probably wouldn’t help much. Right? One consideration is another layer of 5/8″ GWB each side, but the units are occupied, carpeted, there is the end of a base cabinet against the wall in each unit, and the wall outlets would not be flush with the final wall surface. Are there any other suggestions to this problem?
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Well, you already know the answer- you just don't want to do it because of the cabs, carpet, etc. The best solution I can see is another layer of drywall on one side only, since it makes the wall no-n-symettrical, which distors the sound better than adding a layer on each side.
Bob
Bob,
Thanks for the response. I talked to an acoustical engineer in the mean time, and his comment was, as you said, at least one more layer of GWB. He also recommended using RC Channels on one side at the same time. That's what I will recommend.
The only other retrofit alternative would be to pump in lightweight concrete into the wall cavity, in 8" lifts, let it cure, and then more 8" lifts etc. so as not to bulge out the walls as you progress upwards. This would make it similar to a concrete block wall. JUST KIDDING!
David
A different approach may be to install full length lined drapes to help baffle the sound But keep any fire code issues in mind with that.
Adding a extra layer of rock to the wall you need to isolate the second layer for maxim results since sound travels through solid material in waves.
Use blobs of drywall glue on the 2nd layer and no screws/nails in the field. The glue acts as a noise damper.
Thanks, sounds like a good inexpensive solution. I will keep that in mind in the future.
arktect
Thanks,
Drapes would have to be the condo owner's perogative.
RC Channels, which I will suggest, would isolate the GWB from the studs.
David