Ceiling Support

[bloeff]

Hi all,

I'm converting a mobile home bedroom into a recording studio. I'm building a room within a room for sound isolation. Right now, I'm down to studs and subfloor.

My plan is to attach 2x4s to existing top plates and studs at opposite ends of the room to act as ceiling rim joists for the new lower ceiling. I'm going to run either 4x4s or sistered 2x4s to act as ceiling joists with each end hanging in a 4x4 joist hanger. Which would be better?

The joists will be perpendicular to existing trusses. The span is 13 feet. At midpoint of span the joists will be attached to what appears to be a 2x2 that is part of an existing truss to prevent sagging. I will also cross-brace all joists to improve rigidity.

Two 1/2" layers of drywall will be hung on the joists. I would go with bigger lumber for joists, but I'm already cramped for headroom (floor will also be raised).

I couldn't find much data on such a setup. Will this structure support the drywall? How much of the load will the center truss bear? Will it be excessive?

To handle all the extra weight of the room, I will install perimeter blocking under all the outriggers under the room.

Any advice would be greatly appreciated!

Thanks,
Bruce

 

[theprinceofdarkness]

Where you hang your new joist from an existing bit of structure, I think you should use some form of rubber isolation, same as where the floor is sitting on the old structure. A mobile home is an extremely lightweight structure and I think you will be disappointed with the results. The door(s) will have to be air sealed and upgraded likewise the window(s). In studios, they use triple glazing about 6" thick with the internal pane sitting at an angle and the inside of the frame covered in sound absorbing material.
Frank

 

[bloeff]

Thanks, Frank. I went over the plans with a builder of 30 years. He was kind enough to print out an engineering sheet showing that the structure would exceed all building codes. I'm going a step further than what he suggested, just for my peace of mind - installing support pillars under the outriggers.

My main structural question, however, remains. Will the ceiling joist structure be strong enough? Sistered 2x4's or single 4x4? Two builders have told me that it would be strong enough, but I'm still a bit skeptical about the 13' span. Having never done anything like this before, I want to get as many professional opinions as possible, again, for my peace of mind.

As far as the isolation, I'm going with double layers of 1/2" drywall with green glue in between for the outer wall. There will be a decoupled inner wall of steel framing with double drywall and green glue on the inside of that (soundproofing insulation in between). And as you stated, my best attempt to decouple floor and ceiling.

Even though this is a mobile home, I think that the soundproofing technologies will produce an STC 55-60 room (some tests show much higher, but I'm not getting my hopes up). Having no windows will also simplify the design.

Thanks again,
Bruce