Stud wall weight tolerance with floating joists/ceiling

[DaveC80]

I am soon to begin construction on a sound insulated room within a room in my garage, and have almost every aspect figured out, but one thing I am having trouble determining is if my stud walls will be strong enough to take my floating ceiling joists and the weight I'll be putting up there.

I know the joists themselves are the correct and required size at 47x150 (finished), as there are tables to determine this based on the span width and weight of the dead load (there is no live load in my scenario)... and that is just under 30kg/m2 (two layers of PB and insulation). So on this aspect I am clear.

For space saving, given the room isn't very wide, my original plan for the stud walls was to use 3x2 one side and 4x2 the other. The CLS I'm using for the walls is regularised to 38x63mm and 38x89mm respectively. You may question what's the point just to gain 1.6cm, but I discovered that if I went with two walls at 38x89mm, the projector screen I was planning to put in the room won't fit, and I'd have to drop to a screen 10" smaller.

The problem is that I cannot find any tables or guides which indicate what thickness stud walls should be to take the weight of the joists and ceiling, so I don't know if what I have planned is OK, or if I need to lose the idea of the thinner wall and have both at 38x89mm? Assuming even that is enough? I don't know if any problems could arise having two walls of different thicknesses, given the joists would obviously be resting on a greater surface area on one side vs the other (albeit only 1.6cm different).

Can anyone advise? Many thanks.

 

[Deleted member 174758]

To maximise the wall stiffness you may want to consider gluing and pinning a layer of 3mm plywood onto one face of the walls. The ensure that you can carry the loading of the ceiling it might be as well to double-up the header plate of the wall framing on the thinner wall unless you can arrange for the joists to sit directly above the studs