on my inner walls on the back side my friend told me about hanging thick roofing felt on the back side then of cours dead air space and then the outter wall. so on my inner wall i would have 2 layers of 5/8 sheet rock rockwool bats then heavy roofing felt stapled to the back side of the studs. any thoughts on this? it seemed like a cheap way to get better stc levels.
roofing felt between walls
Originally posted at johnlsayers.com, topic 3341.
I don't think that will do very much for you - as the felt is so thin - plus it's not sealed off. STC is not so much important as Low-Freq T.L. I believe that the low freqs would go right through the felt. Your best bet is mass, air, mass. The more mass and the bigger the air gap the better.
Your double layer rock, mineral wool and air gap should be just fine.
Jeff, can you please follow these guidelines so we can help?
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=3231
If you can include a sketch of what you have so there's no misunderstanding, we can make sure whether you're on the right track or not... Steve