Drywall STC Ratings

[mooser]

Greetings,

In an Owens-Corning presentation about one of their sound-proofing systems the company said 16 layers of 1/2" drywall (alone with no insulation) are needed to achieve an STC rating of 45.  Is this so?  Is there test documentation somewhere verifying the statement?

Thanks.

[johnbergstromslc]

Maybe you'd need 16 layers of drywall all put together in one monolithic slab to get an STC of 45, but on a standard wood stud wall, you can get STC 45 with 2 layers of 5/8" drywall per side, with absorptive insulation in the cavity.  Without any insulation, you'd need 4 sheets of 1/2" per side - 8 total (the wall would be 7 1/2" thick).  

Adding resilient channels, staggered studs, steel studs or double walls will raise the value even more.

[joel]

hi mooser,

Why use all that dry wall when you can get 45 STC assembly with bonded cotton insulation and one layer of 5/8" dry wall?  See the acoustic specs at http://www.soundproofing.org/brochures/SSP%20Cotton%20Fiber%20Insulation.htm  And these ratings are with a wall assembly that is open on the other side!  Close up the "back" side and get even better results.

Joel