Questions on RC-2 Installation

[TomF]

Hi !

I'm getting ready to install the ceiling in my basement studio. I've installed R25 (8 1/4") between my 2x8 wood joists which are 16"oc. I'm using RC-2 with two layers of 5/8 rock. The drywall supply house where I found the RC-2, suggested I first install Georgia-Pacific Hushboard to the 2x8's, then the RC-2 , followed by the 2 layers 5/8" rock.
(http://www.gp.com/build/product.aspx...1&hierarchy=pc )
Do you think it would be beneficial to install this Hushboard or not?

Also the drywall supply house recommends installing the RC-2 , 16"oc for a ceiling , but searching the forums topics ,I've found suggestions for 16"oc and 24"oc.
How should I install it ,16" or 24" on center?

Thanks in advance!
Tom

[z60611]

You should search this forum for 'fiberboard' and 'homasote' for some other opinions. I hear it's great under a steel barn roof to reduce the noise of rain. And some people have tried using it inside the room as an absorber of sorts.

The short answer is I wouldn't bother with the Hushboard in a gypsum wall (Hushboard is "Lightweight, low-density", similar to http://www.homasote.com/ or Celotex Sound Board). IMO if you have the cash upgrade to another layer of gypsum, or some isolators (RSIC instead of RC).

Another way of thinking about it is that one of the possible benefits of using Hushboard would be to decouple the wall a bit, but you're already talking about using RC which should do a much better job at that than Hushboard. Certainly Hushboard won't contribute much mass to the wall, and mass is a good thing from a soundproofing point of view.

From http://www.cmhc.ca/publications/en/r...ch/02-108.html

Installing resilient furrings on wood stud partitions is much more effective than a fiberboard panel to mechanically decouple the gypsum board from the structure of the partition and hence to increase its sound transmission loss, especially above 250 Hz.

A conventional 2 x 4 stud wall with 1/2" gypsum board will achieve a Sound Transmission Class (STC) of 38. That will make loud speech in the next room audible as only a murmur. Premium-construction gypsum walls with isolators can deliver STC ratings of 56 to 63, and double stud into the 70's. Loud speech in the next room would not be audible. Gypsum used with a steel stud wall can help achieve high-quality sound isolation with an STC between 47 and 60. (Source SAE).

vs from the Hushboard page

A conventional 2 x 4 stud wall using Hushboard and 1/2" gypsum board will achieve a Sound Transmission Class (STC) of 39. That will make loud speech in the next room audible as only a murmur. Premium-construction, sound-isolated walls with Hushboard can deliver STC ratings of 56. Loud speech in the next room would not be audible. Hushboard used with a conventional steel stud wall can help achieve high-quality sound isolation with an STC of 49.

This quote, from your Hushboard page, was just wierd to me. Gypsum stops a lot of high frequency noise on its own.

Hushboard traps higher frequencies of noise, and the gypsum reduces transmission of lower frequency noise.

The order of panels you've suggested, may be a weak triple leaf. {studs, hushboard, RC2, gypsum, gypsum}, which is a bad thing. I assume you're putting some sort of insulation between your studs, and you're not just using the Hushboard as insulation. An alternative order that wouldn't be triple leaf would be {studs, RC2, hushboard, gypsum, gypsum}.

For more details have a look at NRC's ir761.pdf, and compare fiberboard against other constructions. While there are not great comparisons in there between fiberboard and otherwise identical walls, it will give you some ideas about other constructions that may be better for you, in a cost benefit sort of way.

For another varient, here's

We live in a townhouse and our bedroom wall is shared with the neighbors kitchen and living room wall. They are up all hours of the night and the sound was loud!
We hired a contractor to come in and put insullation and what he called soundboard and drywall in. It didn't do anything to soundproof. In fact, I swear it amplified the noise and he then walked off the job."

( http://www.acousticalsolutions.com/c...e_study_13.asp )

(I've never built anything)

[knightfly]

That last quote is 'way too familiar - I've talked to quite a few "drywall contractors" who have "tried RC and it doesn't work" - without exception, when I asked how they installed it they said that they put it over the wallboard on one side, then added either one or two layers of wallboard on the RC. And guess what - they were right, it DIDN'T work. You would actually be better off not using RC at ALL than putting it up so you have another air gap.

If you don't think two layers of gypsum on resilient channel will get you quiet enough, you should spring for RSIC clips and channel, put two layers up, seal them and see how it is - if it's not enough, you'll have the strength to add a third layer of drywall - the other "magic" stuff mainly "magically" enhances the profits of the seller. Mass kicks ass, and drywall is the most reasonably priced mass you can buy... Steve