Would this be a 3rd leaf or just a roof?

I can't figure this one out. The cieling of my studio has one (so far) layer of sheetrock screwed into the framing above it. On the other (attic) side of the framing there is nothing. Then there is the huge air gap of the attic, and then finally the framing for the roof. The roof is covered in plywood and then roofing material. Is that so much space between "leaves" that I should add another layer of ply or sheetrock on the attic side of the cieling framing to make a nice 2 leaf structure, or is that adding an extra leaf between the leaves of the cieling sheetrock and the far away roof plywood? How much space has to occur before the next layer of a structure is no longer a leaf? :cry:

In your room, install the mass directly to the existing ceiling sheetrock. This keeps you in a good situation, is a lot easier to do then installing into the attic area and is overall more easier to do. You are correct in your thinking that the configuration displayed will produce a three leaf. A leaf is always a leaf. But it is not always as determental as it seems. In your situation, if you massed up the attic side of the joists and created the three leaf, then you would most likely have a reduction in low frequency isolation which is what you do not want and is a direct result of a three leaf assembly. But if you >could< add more mass onto the top side of the joists that made it more dense then the roof, then the system you had might negate the 3 leaf effect by sheer weight alone. So I wouldn't do it personally but math is not my strong suit. Sad for a carpenter to say.

LOL. Thanks, xSpace! Actually quite relieved as working in my attic requires the flexibility of a contortionist and the patience of a saint. Of which I have neither. I will be adding mass to the inner leaf.

another aspect of your situation is that the cavity between the ceiling and the roofing is not sealed, in fact by law you will probably require ventilation via under the eaves. Because the air is free to move in and out it can't act as a spring in a Mass - Spring - Mass situation. So in reality you can't class the roof as a leaf.

True, the attic is not sealed. If the roof is not in fact a leaf, then I must add a layer of mass over the ceiling in the attic to arrive at a M/A/M situation. Thank you!