All walls and roofs are 4" or 2" thick "double wall" construction. Exterior of panels are minimum 16 gauge galvanized steel. The inner walls are minimum 20 gauge perforated galvanized steel. The insulation is 4.0 lb./cu tf. density mineral wool. Walls are all turned inward to provide a clean flush finish. All joints are sealed with urethane sealant. Each panel is joined together with a number 14 tech screw on 8" centers.