Wall/Ceiling Plasterboard Thickness

Hey guys, Happy New Year! Hope the Holiday Season was good to you all. I have what is (hopefully) a straightforward question concerning Gyp Board thicknesses. I have 2 options to choose from: 3 layers of 10mm (3x0.4") or 2 layers of 13mm (2x0.51"). Which would you guys recommend as providing the best isolation value? Obviously the 3 by 10mm has more mass, but mass isn't ALWAYS the answer... I'm also concerned by the weight. 3 layer (3x10mm) weighs 4.24 pounds per square foot whereas 2 layer (2x13mm) weighs 3.65 lb/sq ft. The walls arent a concern so much as the ceiling. I imagine that the increased rigidity of 13mm thicknesses would be better suited for a well-supported ceiling layer, plus weighing less than the 3x10mm has got to be good as well. That 0.6 lb/sq ft difference works out at a difference of 200 pounds! (Room is 23x15 feet) It's actually CHEAPER fo get 3 layers of 10mm than 2 layers of 13mm. From a construction point of view, would gluing the sheets together as well as fastening each layer to the ceiling stud make them more rigid? Would this decrease isolation as they would all move together rather than over each other if they were not as rigidly bound? Basically I'm after the best solution. Structural integrity has got to be priority number 1, but I'm also looking for the best isolation shell possible. Which way would you guys go? Any tips for either method? Thanks a lot! Hayden

" but mass isn't ALWAYS the answer.." Mass is always the answer, the rubics cube is how do you get the mass you need to establish the isolation you require. Thicker is always the better but you need to get up to 15mm to start making a difference, as data supports and we can verify. "From a construction point of view, would gluing the sheets together as well as fastening each layer to the ceiling stud make them more rigid? " That is a ceiling joist. But the gluing together of the sheets will reduce the overall ability of the panel since the multiple panels reduce the center frequency of the wall assembly, low frequency loss. "but I'm also looking for the best isolation shell possible." What we are discussing is the interior shell, we have not even opened up the whole can of worms that is the exterior shell.

I have 2 options to choose from: 3 layers of 10mm (3x0.4") or 2 layers of 13mm (2x0.51").

The answer is "none of the above"! :) The answer is "at least one layer of 16mm drywall". 12 mm (and most definitely 10mm) are too thin to be good for high levels of isolation. They are too flexible, the mass is too low (as Brien already pointed out), and the resonant characteristics are just not there. A single layer of 16 mm drywall will beat two layers of 10mm, and two layers of 16mm drywall will absolutely outperform either of your options. Even though the total mass is apparently similar, the difference in isolation is not.

I'm also concerned by the weight.

Yup. :) Isolation requires mass. You can't isolate without mass, and there are no magical materials that can somehow bypass the fundamental laws of physics. Without enough mass, you cannot get isolation.

I imagine that the increased rigidity of 13mm thicknesses would be better suited for a well-supported ceiling layer,

Not really: You didn't say what your isolation requirements are, but rigidity only matters in certain zones of the spectrum, and for certain reasons. Notably, the very low end, below the MSM resonance of the wall assembly, and up higher, around the coincidence dip. In between, it is the resonance itself that matters most, followed by mass law. So don't get stuck on rigidity (stiffness) unless you happen to have major issues with low sub-sonic sounds...

From a construction point of view, would gluing the sheets together as well as fastening each layer to the ceiling stud make them more rigid?

What Brien said: Listen to the man! :)

Would this decrease isolation as they would all move together rather than over each other if they were not as rigidly bound?

Yep.

Basically I'm after the best solution. Structural integrity has got to be priority number 1, but I'm also looking for the best isolation shell possible. Which way would you guys go? Any tips for either method?

Like Brien said, there are two parts to your isolation shell: the inner leaf and the outer leaf: They act together, in unison, as a MSM resonant system, so everything matters. If your outer leaf happens to be walls of two-foot-thick high density reinforced concrete, then concrete indeed skimp on the inner leaf construction. But if you have a typical house or garage as your outer leaf, then that is a whole diferent thing... - Stuart -