Assembly Detail at Existing CMU Wall

[mickeymullen]

Hello all,

Renovating our office area, and I'm using the opportunity to turn my office into a project studio. I tried attaching full set drawings but the file is 800Kb. Here is a link https://gtimillwork-my.sharepoint.com/: ... w?e=nU4gBu I attached a screen shot of just the wall type drawing.

The northernmost office is the room in question

We have to use metal studs due to the code classification of the building

Planning on double stud walls with resilient channel and multiple layers of drywall

Here's the question- The existing eastern wall is CMU. Ive been looking for the proper detail for the new wall against the CMU. (Wall type W-1)

The architect indicates installing the metal studs directly to the CMU. I am assuming the detail would be CMU- Metal Stud- air gap- metal stud- channel- 2 layers drywall

Is this acceptable for sound isolation purposes?

I apologize if I have not followed the rules for first time poster- please let me know if I failed to comply!

[Soundman2020]

Hi there "mickeymullen", and Welcome!

I'm using the opportunity to turn my office into a project studio.

Is this on an upper floor in an office building? Are you planning to record live instruments? If so, then you are probably going to have a tough problem isolating your floor. Most studios are built on the ground floor, where the concrete slab rests directly on Mother Earth. Slabs on upper floors are basically drum heads, want to resonate and vibrate and transit sound, not stop sound.

We have to use metal studs due to the code classification of the building

OK, so your ceiling is going to be a problem too: structural metal studs that can span long distances with heavy loads, are hard to find. Better look around your local building supply stores, and ask your structural engineer about that. He'll have to figure out what gauge and size metalwork you are going to need.

Planning on double stud walls with resilient channel and multiple layers of drywall

That room already has walls around it, so you don't need two MORE sets of studs: You only need to add one more leaf, not two.

And if you are using decoupled stud framing for the inner-leaf, then you do not also need resilient channel. If the framing is decoupled, it makes no sense to decouple again, and in fact can potentially make things worse, rather than better. If your framing is NOT decoupled, then you could use RC, but it is far better to decouple properly.

The architect indicates installing the metal studs directly to the CMU.

Bad idea! ALL of your inner leaf framing most be completely decoupled from the outer leaf, on all sides except the floor. There can be no mechanical connections at all between your inner-leaf framing and the outer leaf. Your inner-leaf walls rest on the floor, and your inner leaf ceiling rests on top of those walls. None of that can touch any part of the existing structure at all. Not even a single screw.

That's what "fully decoupled" means, in acoustic terminology. The only thing connecting the two leaves of the wall, is empty air (and the insulation in that air, but that does not count as a mechanical connection...).

I am assuming the detail would be CMU- Metal Stud- air gap- metal stud- channel- 2 layers drywall

No. The CMU wall IS your outer leaf, and needs no framing on it. So it would just be "CMU - Gap - Stud frame - Drywall" (with suitable insulation filling the entire cavity, of course). Don't get confused regarding the "air gap" and the "framing gap". There's a gap between the CMU and the inner-leaf framing, yes, but that's not the air gap. The air gap is the complete distance across the cavity, from the face of the CMU to the face of the drywall. That's what matters here, since that's what the sound "sees" as it moves through the wall. It doesn't care about where the studs are... it just sees the two leaves, and the air in between. And that air has to be filled with suitable insulation.

Is this acceptable for sound isolation purposes?

Not really.

The image below shows what you are trying to achieve. It uses wood studs, not metal, but the concept is the same:

MSM-two-leaf-WallChunk-conventional--NOT-inside-out--one-room--S06.png

The inner-leaf is completely separate from the outer-leaf. The ceilings are not show here, fore clarity, but they are done the same way: the inner-leaf ceiling rests ONLY on the inner leaf walls, and the outer-leaf ceiling would be a short distance above that.

- Stuart -

[mickeymullen]

Is this on an upper floor in an office building? Are you planning to record live instruments? If so, then you are probably going to have a tough problem isolating your floor. Most studios are built on the ground floor, where the concrete slab rests directly on Mother Earth. Slabs on upper floors are basically drum heads, want to resonate and vibrate and transit sound, not stop sound.

1st Floor in a 1 story building. Concrete slab shared by woodworking machinery EDIT:(But not planning on doing recordings during business hours )

That room already has walls around it, so you don't need two MORE sets of studs: You only need to add one more leaf, not two.

And if you are using decoupled stud framing for the inner-leaf, then you do not also need resilient channel. If the framing is decoupled, it makes no sense to decouple again, and in fact can potentially make things worse, rather than better. If your framing is NOT decoupled, then you could use RC, but it is far better to decouple properly.

See Demo plan. Existing walls are the CMU walls on the east and west. all walls within the renovation are new

I am assuming the detail would be CMU- Metal Stud- air gap- metal stud- channel- 2 layers drywall
No. The CMU wall IS your outer leaf, and needs no framing on it. So it would just be "CMU - Gap - Stud frame - Drywall" (with suitable insulation filling the entire cavity, of course). Don't get confused regarding the "air gap" and the "framing gap". There's a gap between the CMU and the inner-leaf framing, yes, but that's not the air gap. The air gap is the complete distance across the cavity, from the face of the CMU to the face of the drywall. That's what matters here, since that's what the sound "sees" as it moves through the wall. It doesn't care about where the studs are... it just sees the two leaves, and the air in between. And that air has to be filled with suitable insulation.

I am interpreting this as North, West and South walls are double stud construction (GWB- Metal Stud - framing Gap- Metal Stud- GWB). East wall will be a single stud assembly 1" off the CMU with GWB on the office side. No RC required at all. Am I reading this right?

Thanks for the help!

Additional Question:

Should I be pushing for 25 Gauge studs on 24" centers? or is the difference between the light gauge and heavy gauge negligible in this scenario?

[Gregwor]

You have your MSM system drawn wrong. Follow your walls. Your inner leaf walls cannot touch your outer leaf ANYWHERE.

Greg