D&D,
Hi Dan, havent seen u since Ferry Farm. Maybe see u on the VMI proj.
Your guidance on moisture barrier on the warm side of the structure is in sync with my prior experience and training.
back to air relief for the metal roof. The Muellar Co in TX is a proponent of using some mylar backed closed cell foam bout 3/8" thick underneath it's 36" wide steel roofing. Shiny side up. this puts a smooth surface under the integral channels in this standing seam look alike and when topped with vented ridge the air wash helps in solar reflection and moisture reduction. The foam also serves to seal the stainless screws coming thru the panels to hold them down (in concert with the live rubber compound sealing washers under the screw heads).
So we end up with a cool, dry, solar reflecting and very light weight roofing system at reduced cost. hmmmmmmmmmmmm