Lightweight Ceiling Considerations

Hi all, I'm new to this forum, but have been browsing for months. I am building a small studio in a converted one-car garage. The building is 23' x 13'. The ceiling is 7' at the edges, and 9' in the center. My problem is this: the trusses are on 48" centers, and are 2x4. We have beefed them up with bracing, but I do not think I can hang much weight on them. We figured we could put two 5/8 gypsum layers on. The roof will be well-vented, and is just 1/2 OSB and steel, so I will not count it as a leaf. Thus my two leaves will be above and below the 2x4 studs we ran between the the trusses (on 24" centers). I want to use RSIC clips on the ceiling side. I want to have at least two layers on my leaf, and was wondering which combination would be best: - Two layers of 5/8 gypsum with green glue on ceiling side, isolated with clips and hat; and two layers of cleotex on roof side with green glue, plus R-11 fiberglass in-between, and R-20 blown-in above, -or one layer of gypsum green-glued to celotex, on both sides (roof and ceiling) again, ceiling side isolated and same insulation setup. Or is there an even better, lightweight method I don't know about? Don't have to worry about permitting, and have built several shops and houses. Also, on the walls, it will be an inner 2x4 stud wall with R-11 fiberglass and two 5/8 gypsum boards. the outer leaf is a sperate wall, with two 5/8 gypsum and R-11. So the two walls are seperate. What would be the better investment: RSIC clips or Green Glue with RC channel. Is it necessary to do both walls, or just the inner? Will probably use RC with both walls, as it is cheap. I am not real worried about bothering the neighbors, as they have an MX track... that is MY problem. Also in a flyway, so I have some jets to deal with. This project is still in the early stages; it can easily be changed, except for the floor, basic roof, and basic outer wall (Which is just 1/2" particle siding, and well-vented, so I don't count it as a leaf either.) I do have Rod's book, it is a very good reference, and have read it several times. Thank you, Jason

Read the stickies! Oh, wait... You obviously already did that. Buy Rod's book! Oh, wait... You obviously already did that. Study the projects here! Oh, wait... You obviously already did that. Don't forget the issue of permits! Oh, wait... You obviously already did that. (So, out of curiosity -- how come it's not an issue? Accessory building exemption or some such thing?) Celotex? That's a manufacturer of many products. Are you referring to their "sound board" product? If so, I suggest you avoid it and use either drywall or OSB instead: drywall if it's for sure going to be completely dry 100% of the time. Drywall (as I'm sure YOU know) is cheaper and denser than OSB, but OSB is superior in its shear strength and tolerates an occasional spritzing, provided it has an opportunity to completely dry out. Sorry if I missed it, but it's not clear to me... Are you supporting your inner leaf ceiling on new joists fastened to the tops of your new inner leaf walls? If so, then you can totally skip RC and/or RSIC clips with hat channel. Separate frames = decoupled already, so there's no need to KINDA decouple with those compromise products. The Green Glue will be especially good for you on your ceiling, particularly the "middle leaf." (And let's be homest: that WILL be a three leaf deal. However, the liberal venting will HELP MITIGATE the dreaded third leaf effect. Thinking out loud: spray foam insulation on the underside of the roof MAY HELP A LITTLE as a resonance damper... MAYBE. Don't take my word for it... But it MIGHT be worth looking into if you need that extra notch of performance.) It will increase the performance significantly without costing you the weight, which is at a premium in your case. Obviously, be 1000% certain your beefed up trusses are up for the job. A structural engineer would be a good investment in keeping everything and everyONE absolutely unflattened. Great start. Looking forward to more questions, illustrations, and of course, PICTURES! :-D Keith :mrgreen:

Thanks for the response. The building permit is not an issue because we are outside city limits, and the counties in MT don't really care what you build (as long as it is not a pig farm!) Yes, I was referring to soundboard when I said celotex. With the truss situation, we cannot add much more mass than two layers of 5/8 drywall. I forgot to mention, there will also be one layer of 1/2 OSB on the ceiling side. The ceiling will be completely dry, the spray foam is a good idea, We have done that in our shop. The ceiling will NOT be suspended from new joists supported on the inner wall. I wish it were so, but I don't think we can wrangle it with our space considerations. I will definitely look into it, though. The new trusses we built are an arch design, and can support a lot more weight than the straight trusses that were there before. I will try to get some pictures up. I hope the three-leaf problem will not be too apparent! Several questions: -Which is more bang for the buck, green glue or RSIC clips? -Is it necessary or even worth isolating an outer wall, if an inner wall has already been isolated (i.e. with RSIC or RC)? Obviously not with a decoupled wall. -Finally, if I use only two layers of drywall in the ceiling, should they both go on the same side, with OSB on the other, or one on each side? Thanks, Jason