Is there any way to have the roof framed such that the framing height is only 2" but has sufficient strength?

Question

I basically have to make a walk in chamber inside a laboratory and the height of the laboratory limits the height of my chamber. More-over the chamber is to be lined in with wedges which are 13.5" in depth. Considering that and still trying to make it a walk-in chamber, I have very little left for the framing. I tried putting 2x4 studs flat for the roof and my calculations gave me a deflection of 0.5". Can I enforce it somehow without incresing the height of framing?

Answer 1

you might want to try bolting "L" brackets of the same length as the 2x4 to two sides of the wood this should stop the deflection   11/2x11/2 should work perfectly

Answer 2

Can you give us some more details? What is the total height to the lab ceiling? What is the purpose of the chamber (Airtight? Soundproof? etc.)? How much weight will be on the roof? What are the plan dimensions of the chamber? Could you elaborate on the wedges, and how they are relevant?

0.5" sounds like a lot of deflection. Either the chamber is big (could you add a column?), or there's something heavy on the roof.

Does the chamber even have to have a roof? Can you attach the walls to the lab ceiling so it acts as ceiling for the chamber also?

Edit: I concur with your calculated deflection of 0.5" (I used a span of 10'). I assumed you have the joists touching (spacing 3.5"), which is as strong as you can go with 1.5" thickness.

Can you spare another 3/4"? If you take those 2x4 joists and glue them to sheets of 3/4" plywood, you get a structural panel of depth 2.25", but its moment of inertia goes from 3.375 in^4 per foot of width to 11.4 in^4. Given the same wedge load (I used 5 psf), you get a deflection of 0.14", bending stress of 178 psi, and a horizontal shear stress of 3.33 psi - all well within allowable levels for pine lumber. Note that every joist must be 100% glued to the plywood to get the composite action and the higher moment of inertia.

Could you sacrifice the thickness of your floor framing if necessary?

Could you add stiffeners along the top of the roof, strategically located to miss the I-beam and water pipes? Do they all run the same direction?