I'm running the numbers for enclosing a 2000 sq ft structure. I've got no end of 1 inch white pine T & G rendered out of the logs that gave us the timbers. I'd like to lay it diagonally across rafters on 36 inch centers, for aesthetic and stiffening effects. Is there any killer reason not to put a thick nailbase EPS panel (OSB on top side only) on top of that, and then apply roofing. What TYVEK, vapor barrier, roofing felt, etc. is recommended? Would more expensive polyisourethane sandwich panels be worth the cost?