Ceiling Diaphragm

[SteelPE]

I am designing a garage that is 48’x60’ with 16’ clear. The roof members are going to be wood trusses spaced at 2’-0” o.c. The contractor decided to use OSB attached to the underside of the wood trusses to act as a diaphragm for the wall studs and gable end (actually they are going to apply OSB to the entire inside of the building, no gypsum,).

I was wondering what span rating panel I should use for the diaphragm? Since it is going to be 16’ to the roof trusses, and no stairs are currently located in the structure I don’t see the owner applying any vertical load to the diaphragm. I currently have a 24/16 sheathing shown on the drawings and would like to know what other people would do in this case.

 

[Ron]

Why did the contractor make the OSB decision? That should be your decision.

As for the 24/16...I'd stay with that, using 1/2" nominal as a minimum thickness.

Does your dead load consider the wood as compared to gypsum?

 

[SteelPE]

From what I can see it doesn’t really matter what the type of panel is does it? As long as you have the span rating and the diaphragm capacity OSB or plywood shouldn’t matter. The code doesn’t distinguish between the two.

My decision, makes is sound like OSB is bad. All I am doing is trying to work with the contractor

As far as my dead load goes, I am using 25 psf, which should be enough for 2 layers of shingles, 2 layers of sheathing and the weight of the truss.

 

[MiketheEngineer]

Make sure it is APA rated OSB....There are a lot of imitators out there - including plywood..

 

[FSS]

Span rating will not matter. They will probably use 7/16" OSB, although even 3/8" would still work. You will have pretty good diaphragm action all over the place with OSB instead of drywall. No worries.