Hello!  I have a simple 45×45 metal shell barndominium in the central Texas hill country.

Welded construction, not bolt up.
4×4 structural steel square tubing for vertical supports.
4″ steel wall purlins.
8″ structural steel roof beams.
8″ roof purlins.
R panel walls and roof.
12′ walls.
Gable roof.
4/12 pitch.
19 feet to peak.
Maximum span between roof and wall purlins is 5 feet.

Front half will be kitchen, dining and living with vaulted ceiling to peak.
Back half will be 2 bedrooms, 2 bathrooms, hallway, closets, etc, with loft above.

Engineered wood floor joists for the loft will have to accommodate HVAC ducting.  My plan was to install 2×4 lathes (lumber) on 16″ centers, as opposed to 2×4 studs on 16″ centers, on the walls and ceiling.  The idea being the 2×4 lathes will be screwed to the 4″ purlins then sheet rock installed directly on the 2×4 lathes.

1.  Is this structurally sound or not?  Other concerns?

I plan to insulate using open cell spray foam sprayed directly to the R panel sheet metal, no vapor barriers installed.  3″ to 3-1/2″ of foam on the walls and 5″ to 6″ of foam on the roof.  There will be an air gap between the sheet rock and the foam.  I’m not concerned about condensation because warm moist air should never have an opportunity to contact a cold surface inside or outside (if sprayed correctly).

2.  Does this make sense or not?  Other concerns?

Any and all feedback is greatly appreciated!

Thanks!