Drywall-Homosote-drywall or Homosote-drywall-drywall?

[NigelT]

I am building inner walls in an existing studio. I want to know if either method of layering is more effective than the other. Thanks for any input

[Gregwor]

Homasote doesn't have as much surface density as the equivalent thickness of drywall does. You can easily see the difference in performance by choosing the different combinations in this transmission loss calculator:

http://www.johnlsayers.com/phpBB2/viewt ... =1&t=21770

Greg

[SGleason]

Here at the Homasote Tech Desk I have kicked this question around anecdotally with a few consultants but there is no hard data on either side of the question.

One theory is that Drywall/Homasote/Drywall becomes a constrained layer damping assembly allowing the Homasote to act as a spring on two layers of GWB. This installation has GWB facing GWB in the cavity and that comes to bear on cavity resonance.

We have found that an "unbalanced wall" performs a bit better. By that I mean a wall that has the Homasote/GWB on one side and just GWB on the receiving side. We actually have a steel stud wall test that has Homasote on both sides and performs the same as the assembly with Homasote on just one side. Theoretically, with Homasote facing GWB across the cavity the resonant frequency of the cavity lowers due to the lack of symmetry in the respective absorption coefficients.

With regard to the question, there has been no consensus in my discussions. I like the asymmetrical cavity resonance approach so I always advise Homasote/Drywall/Drywall for folks who need a 2-hour fire resistance assembly..

I apologize for any improper verbiage on all this. I'll appreciate any corrections and any opinions on the theory.

Steve

[NigelT]

Thanks for taking a look Steve. I never had data or proof, just a theory that H-D-H would have a damping effect as you said, but now I know better. I think I won't bother with the H at all. Time and money for little gain. I bet a third layer of drywall would give better results
Regards
Dave
P.S. your verbiage is adequate.