Solving an existing wall problem....

Hi guys...and gals! Again, excellent forum. VERY helpful. I'm still in the "learning" process of studio construction. (do you ever really stop learning????) I'm studying building methods and trying to gather all the knowledge I can from you guys. I don't have an actual build in the works so there are no details to give. I am just trying to learn the ins & outs to prepare for possibly a future build. Someday. I am located in Nashville, TN. Here is my question. For the most part I understand the MsM rule and it's making sense to me. But what do you do when you have an issue like building next to an existing wall that you can not "correct". For example: if someone has a rented space and can't remove the existing layer of sheetrock to properly construct double walls, what do you do? If you can't "fix" Wall 1 how should you construct Wall 2 to have the best isolation? Is the drawing what you would call a three leaf wall? Thanks in advance for any help with this!!! Clint

I would try to carefully remove the outer layers of drywall on the existing wall, fill the framing with insulation and then install the second wall as shown. Is that possible?

Thanks for the reply! I am not currently building, I am just curious what the solution to this problem would be if you could NOT remove the existing drywall. -Clint

In that case, I'm not 100% sure if the existing wall would qualify as one leaf only, since both drywall layers are coupled. Maybe someone more experienced would shime in !

If you cannot remove the drywall on an existing wall, then you have no choice but to build a three-leaf system, which means that your low frequency isolation will not be good. In that case, what you need to do is to compensate as best you can for the lost isolation, and you can only do that with more mass, more air, more insulation, and copious amounts of Green Glue. In other words, you will need to increase your air gap as much as you possibly can, so that your new wall is as far away as possible from the existing wall. I seem to recall a figure of at least eight inches air gap from somewhere but I don't recall where. Even more would be better. Then you need much more mass on that new wall: I'd go for four or more layers of drywall, and at least some of them with GG in between, at what they refer to as "100% coverage". The drywall will double your mass, which theoretically gains you 6 dB of isolation, and the GG will get you some more at the low end, plus the extra air gap helps a lot too. And of course, you would need to fill the entire cavity with rockwool to maximize isolation. Doing those four things would go a long way towards compensating for the three-leaf system. Rather expensive, though. Much cheaper to take off the existing drywall from your side of the wall, use it to beef up the other side from within, between the studs, then add RC, or better still RSIC clips + hat channel, two layers of 5/8 drywall with GG. That would theoretically get you about the same level of isolation overall, and even better in the low end, for less money. But as they say here: "you have to live with what you've got", so the method I outline above would be the best alternative. - Stuart -

If you were to build a new wall in front of the old, how would anyone know if you had removed the drywall?

Thanks Stuart! Excellent and informative reply. That is what I wanted to know. I don't know if any property owner would be THAT closed minded to the drywall removal....I was just curious what to do in that situation. Thank you very much for the "how to" info!