Roof leaf/ ceiling leaf assembly STC illustrations?

[cadesignr]

Hello gents. It seems, if I understand correctly, the ideal floating room assemblys would consist of either a concrete floor slab for the exterior shell, with the floating rooms slabs floated individually upon the grade slab, or the shell floor slab seperated into individual slabs poured on grade, either way isolating the floating rooms from other floor areas in the facility. Walls would consist of Mass-Air-Mass 2 leaf assemblys, with each leaf framing structurally connected to its own floor slab. Correct?
If so, I have a question concerning how to construct M-A-M 2 leaf ceiling/roof assembly, to equal the floating room wall assemblys transmission loss.
I understand thethe concept of a floating room ceiling either bearing on the walls, or suspended between walls via kinetic iso hardware, from a joist assembly or such. But I'm at a loss to explain how, you can sheith a roof to maintain a exterior leaf that has the same transmission loss characteristics as one wall leaf say with 2 layers of 5/8" gyp bd. And SEAL IT. Be it a flat commercial roof, or pitched residential roof, what sort of membrane and construction method or design is utilized for the exterior shell roof leaf? I've read Steves and others solutions for isolating new studio room ceilings from existing ceilings, to create a 2 leaf system, sometimes by compromising the ideal by lining joist cavities with multiple layers of gyp bd, as it is inherently difficult to sheith a ceiling on the attic side of the joists. But how would one eliminate the normal "shell ceiling leaf", to utilize a true M-A-M design whereby the roof was the exterior leaf? I see many illustrations, including Steves, whereby a room is drawn in section, showing the 2 leaf-double wall,double ceiling, but in reality, it seems like a contridiction in reality when it comes to actually building it, unless the roof was the exterior leaf, no? Anyways, its probably an academic excercize, but I'm still interested in knowing, as I have NEVER really seen anything regarding this except ONE picture of a John Sayers built studio, taken in an attic, and shows what I am talking about, yet shows or tells no details of the actual
roof assembly construction. An illustration like the one used here often for STC comparisons of different wall assemblys, would be cool to have for different ceiling/roof M-A-M assemblies, but I've never encountered one. , I think other people who are planning studios from the ground up might also be interested in this area of planning. Thanks for reading this extended exercise in verbosity.
fitZ

[cadesignr]

Now that I think about it, does not flanking occur through the air gap, from room to room, since theoretically, the only thing seperating 3 isolated rooms, is the same airgap and ONE leaf per room? If so, wouldn't this occur in the attic, if it was the airgap over ALL the rooms? How do you minimize flanking around one room to another through the airgap, let alone in the attic? Or, what am I missing? Braincells?
fitZ

[knightfly]

Hey fitz, it's 4am so I'll quickly do your second question, manana for all the rest - the answer to your second question is "insulation" - basically, you have two leaves of mass between ANY two areas you want isolated from each other - then, when you fill the cavities with insulation, you kill convection, and absorb cavity sounds, etc, with all the interstices of insulation. If a sound wave tries to travel ALONG a wall frame, it has to go through several FEET of insulation - transverse, and it's mass-air-mass as usual. The slightly overstuffed insulation also dampens the wall panels against resonance from longitudinal waves (as it does for transverse ones).

For the roof thing vs. 2-leaf, there's a discussion over at RO called "going green" or something, by mad max - check it out.

Gotta get my 5 hours of beauty rest (now you know why I'm so freakin' UUUGLY... Steve

[cadesignr]

then, when you fill the cavities with insulation, you kill convection, and absorb cavity sounds,

Ahhhhhhh no wonder, you FILL the air gap. I was under the impression the insulation was to be held within the stud cavities, and there was supposed to be an CLEAR FIELD in the airgap between the walls.....god only knows why, but thats what I thought. But I think a lot of wierd stuff too Ok Steve, thanks for clearing that one up for me buddy. Like I said, its probably academic at this point anyway, but nothing wrong with growing some new neurons once in a while. At my age, I need all of em I can get. I'll check out the thread at RO.

fitz

[Sen]

Ahhhhhhh no wonder, you FILL the air gap. I was under the impression the insulation was to be held within the stud cavities, and there was supposed to be an CLEAR FIELD in the airgap between the walls.....god only knows why, but thats what I thought.

well, I think it's right. AFAIK (could well be wrong ) only the stud cavities are filled with insul. in most of the cases. And if your air gap is wider than the stud width of both walls added together (in case of a double framed wall) then you will end up with some clear space. And don't forget that the air is your spring (I learned that here I think ) and the more loose it is (bigger air cavity) the better isolation it provides. So you can really say that the clear space (air) to which you're refering is some type of insulation anyway.
I hope some of this is right, coz i think it's time for me to start understanding some of this stuff

good luck