Practical way to raise a inside out ceiling?

Hello all- Was wondering if anyone has applied the concept of an inside out wall to a ceiling, and if there was anyway to build it on some lifts, raise it into place and then build the walls and beam underneath and then lower it onto the supporting structure? In a nutshell I found a place with a 1500sf garage with 13ft ceilings, the garage is basically 50x30' with a steel I-beam running down the middle of the 50' dimension (IE 50' beam with 15' span on either side) outer wall construction is CMU with brick veneer. Above the garage is a residence and the existing joists I believe are 12" on 12" centers. My thought (if it is practical) would be to remove the drywall on the ceiling, add mass to the subfloor upstairs, and seal that all up. Possibly have a spray insulation applied (fireblock required here) and then build (for the live room) 2 ~500sf inside out ceiling sections on the ground (or on lifts of some sort) with a few layers of caulked up OSB to the top of say 18" open web joists, then raise the ceiling (joists OSB and all) up to the existing (outer shell) ceiling joists. Then build walls and a new (decoupled) beam around the existing beam (lam or TJI's) and then lower the inside out ceiling sections onto the support structure. Then use the (now exposed) open web joists to fill with say R29 for acoustic treatment purposes and as a place to attach diffusors, slats etc over. The new open web joists would need to span ~15' so each section would be roughly 15'x30'. I'm told the existing slab is 10" thick! There would still be a flanking path up to the steel I-beam from the slab (through the existing posts), I think it would cost to much to try to remove it and my wife and I would live upstairs so that would be manageable. This would all have to be done by a commercial contractor, so it isn't something I'm looking to try on my own with a used drywall lift or 2!!! We haven't bought this place either, just trying to conceptualize the best way to do something like this so I could roughly work out what all would be entailed. Thanks-

It can be done, yes. I have designed a couple of places like that, with inside out ceilings, and they worked out fine. However, I take a more modular approach, to avoid having to lift very large, very heavy sections. I do smaller modules, sometimes just 4'x8', lift each section into place, rest one edge on the inner-leaf wall, and/or bolt it to other sections, or support it temporarily with jacks until the next section is in place to be bolted together. I also use larger beams than needed at regular intervals across the area (eg, if you calculate that you need 2x8s to span the distance across the room, I use 2x10 beams ever 8 feet or 16 feet, with the modules themselves done with 2x8 framing). If you plan the construction sequence carefully, you can do it. I have also heard of people building the entire ceiling on place on jacks, then building the walls under it, but I'm not to keen on that idea from teh point of view of safety... But don't forget the weight: even a 4'x8' module with a layer of OSB and 2 layers of drywall will weigh well over 250 pounds... that's a lot of weight to be lifting overhead. Make sure you do it safely and carefully. - Stuart -

Thanks Stuart- Very helpful as always, Yeah that makes sense to do it section by section, a lot more practical to lift it that way. And then do you put a strip of 2x4 or something along the edge of each one so that it could be attached/sealed to the adjacent module?

You could do that, yes, but if the studs at the ends of each section are reasonably straight, not bowed, twisted or warped, then just coating the mating edges liberally with caulk and then bolting, screwing or nailing them together tightly will get you a good seal. There's 3-1/2" of seal surface there, and with plenty of caulk, straight studs and good fasteners, that's plenty to ensure continuity of the mass and of the sealing. But if you did want to add another 2x4 on the front for extra insurance, it certainly wouldn't hurt! - Stuart -