I wouldn't do screw down on anything beyond a ag building. Either standing seam or asphalt.
The truss equivalent of a "standard door" or a "standard window". When I worked in a lumber yard, I was amazed at how many people came in or called and wanted a price on a "standard" or "regular" window, and had no concept of different sizes, types, etc. And that was over 40 years ago, I can't imagine it's better now.
I have used 1/4" osb twice and never again. My father's customer wanted it and he eventually paid to have it replaced. 7/16 seems not much thicker, but osb was designed with that dimension in mind. They just don't make a good quarter inch product.
People around here do strong panel on houses regularly. They screw the flats on plywood covered with hip and valley roll with the really sticky stuff. The screws have to have "captive" washers and they will seal on the ice dam or valley roll. I have seen one that acquired a small ceiling stain after 10 or so years.
I know people do it. I'm just saying I wouldn't
And I'm certainly not faulting you for saying you wouldn't.
I didn't mean to imply there is anything wrong w/ the OP's trusses, just that they may not be storage rated.
The metal is impermeable, so no moisture will pass except for the joints. You could seal the joints, but I don’t think it’s necessary. A lot of this has to do with moisture generation in the heated and cool space. Gas heat, cooking, bathroom showers things like that make a lot of humidity inside.
That advice is a little troublesome in cold climates.
Just my opinion but trapping moisture between the steel and vapor barrier seems like a concern. In any case and especially if you heat it you need to seal it somehow. The panel overlaps are pretty tight but the outside edge in J channel is not - need to seal that somehow - I used quite a few tubes of caulk. I had insulation blown in after the steel panels were up.
Its never been a problem that I have seen. In houses I usually have used blown in cellulose but in heated pole barns with liners its pretty common to use a plastic vapor barrier, put up the metal R panel liner, then roll out unfaced batts between the trusses but they are usually on 4' centers.
To the bold.
If you put a vapor barrier in the assembly, like the metal ceiling or 6 mil polyethylene, then you need to design the assembly to prevent condensation coming from either side. This usually involves adding rigid impermeable insulation board like XPS in proper thickness so that the temperature on surfaces anywhere in the assembly never drops below the dew point in any season. I am not a fan of using vapor-impermeable assemblies unless there is dirt on one side.
Yes, vapor barriers restrict the moisture from getting to the surface that is colder than the moist air's dew point. In the winter, even on a day with 100% humidity, there isn't much water in the air. The moisture travels through the exterior and the insulation with ease. It then condenses if the inner surface is cooler than the dew point outside. We can exclude the water with a thin barrier or with closed cell insulation. Closed cell insulation is the same as insulation with a vapor barrier on both sides. If you can insulate to R-6 or so with extruded polystyrene the rest can be fiberglass or whatever because you insured that the surface can't be cold enough to condense under most environmental conditions. If you do your job justice you will have nothing to worry about moisture wise and it sounds like you are headed right.
Don't use 2 vapor barriers
Sure, for a house
My understanding was that code in Michigan for any heated building was R-49. Regardless, I sure wouldn't skimp on attic insulation if the plan is to condition the space. R-38 is pretty light for an attic in Michigan.