Insulation options Existing metal building

[over40pirate]

Just bought a house with an existing 31' x 30' x 7' metal building with a 2 1/2" square tubing frame.
The roof is supported by 2 1/2" sq. metal trusses, with the lower horizontal part of the truss (bottom chord) being 7 1/2' off the floor.

Spray foam is out because of cost. And don't like look if not covered.

One idea is to screw plywood to the underside of the bottom chord. and add lots of fiberglass insulation on top of it. At each end of the roof trusses, is a diagonal brace about 3' long that braces the truss to the wall legs. I would screw plywood th these and the wall legs also, with all seams tapped.
If I did insulate this way, what should I do about a vapor barrier? I'm in SW humid/hot FL and plan on using an air conditioner.

Another idea was to screw foil backed insulation boards to the bottom chord and braces/walls. Tapping all seams. I think this would provide a vapor barrier.
I would put wood at least on the walls. Might even put more fiberglass insulation on top of the rigid insulation.

Then there is the idea to insulate the bottom of the roof panels. Removing the roof panels is not an option. It has horizontal roof/wall panels, with no purlins.
Fitting rigid panels to the underside of the upper chords of the roof trusses, would require a bunch of cutting, and sealing to fit around the diagonal braces.
This method would give me the most headroom, especially between trusses.
If I used this method, what about putting fiberglass insulation in the cavities, between the roof trusses, before screwing on the rigid insulation? Not sure if the reflective surface of the rigid insulation, would work, not having an air space. Also not sure which would be better.

The rigid Polyisocyanurate Foam Board I was thinking of using is 3/4" R5.
Wondering how much the reflective foil facing, along with the 2 1/2" air space, add to the insulation factor.

If I was to use fiberglass batts in the walls, should I put a vapor barrier over it, before putting the plywood on? I think so, but not sure.

Decisions decisions.

Any thoughts, experiences, etc?

 

[Riverside]

There has been some discussion before about insulating tube-frame buildings. I don't think they are engineered to support any significant additional weight. They are sold with the option of radiant insulation (the type that is like bubble wrap with foil on both sides). That might be your best bet, though it is most effective if it is applied between the frame and the sheet metal, to prevent conduction. Foil-backed rigid foam might be your second best option.

 

[over40pirate]

There has been some discussion before about insulating tube-frame buildings. I don't think they are engineered to support any significant additional weight. They are sold with the option of radiant insulation (the type that is like bubble wrap with foil on both sides). That might be your best bet, though it is most effective if it is applied between the frame and the sheet metal, to prevent conduction. Foil-backed rigid foam might be your second best option.

The bottom chord on the steel trusses is doubled up on the building, and the po has used it to pull motors out of cars, so I think it will hold some weight.

I think I read something about bubble wrap radiant stuff not being as good as claimed. Same with Prodex, which is only 5mm thick, and claims R16!

If I have enough headroom, I think a plywood ceiling on the bottom chord of the roof trusses, with 6+ inches of fiberglass insulation, with a vapor barrier might be the easiest, least expensive, and most effective.

 

[over40pirate]

There has been some discussion before about insulating tube-frame buildings. I don't think they are engineered to support any significant additional weight. They are sold with the option of radiant insulation (the type that is like bubble wrap with foil on both sides). That might be your best bet, though it is most effective if it is applied between the frame and the sheet metal, to prevent conduction. Foil-backed rigid foam might be your second best option.

From what I have read, foil backed bubble insulation is ****
If you install radiant insulation (shinny surface) that reflects heat, there should be an air gap between the surface, and the roof. etc.

I've thought of installing a ceiling of the lightest, cheapest material, then putting 9+" of insulation over it. Maybe even a radiant barrier over that.
Still not sure as I may be using the attached garage as a shop, and not insulate the barn. Gable vents for sure. Big ones

 

[Chitown_hillbilly]

I've thought of installing a ceiling of the lightest, cheapest material, then putting 9+" of insulation over it. Maybe even a radiant barrier over that.
Still not sure as I may be using the attached garage as a shop, and not insulate the barn. Gable vents for sure. Big ones

How wide are the trusses? I would think You're going to run into issues spanning the distance with anything light and cheap. What about Ribbed steal panels?

 

[Cruster]

If you are putting in a ceiling and paneling the walls anyway, why not blown in insulation? Way cheaper. Just fill each section. PIA and messy but cheap and easy. Just a thought.