RC on plywood covered wall yes or no?

[aaronscool]

I've only found conflicting information on this (from various manufacturers). I am building a basement practice space/studio which has had an earthquake retrofit. The inside walls have a 1/2" plywood layer as a result.

I was originally planning to do the standard 2 layers of 5/8" gypsum on RC but have read some material that suggests this would not be very effective if there wasn't the normal air cavity of the stud available. Any thoughts on what the best approach may be? RC anyway or just mount the drywall straight to the existing plywood/studs?

Thanks in advance,
Aaron

[knightfly]

I'm not familiar with this particular "earthquake mod", (if it's even a common thing yet) - but if the plywood is flush against the concrete (no air space behind the plywood) you could either put RC and wallboard inside the ply, or (better) add a separate frame and put insulation and your two layers of wallboard inside that. (wallboard ONLY on the inside of the frame)

Which of these you do would depend on the level of isolation you need vs. the space you are willing to give up.

Here is a deep article on basement problems in general, and some fixes -

http://www.buildingscience.com/resource ... ystems.pdf

Your main friends in isolation are two leaves of mass, both airtight, separated by an air/insulation space. The more mass, the better - different construction in the two leaves is better; wider air gap is better.

In-wall insulation can be either standard house fiberglas, slightly compressed (6" in a 4" cavity is good) or rigid board such as OC 703 or rockwool. 2.5 pounds per cubic foot has been found to be ideal balance between bass and high freq attenuation. The rigid stuff doesn't seem to do much better than the batts, and batts are cheaper.

What does NOT work well is more leaves and more air gaps. They will actually REDUCE the isolation in some cases... Steve