This may be a thread on here, but I couldn't find exactly what I'm looking for. I'm in the process of framing in and insulating my (new to me) pole barn. it is a typically constructed post/frame with 2x4 purlins every 2' o/c with metal siding. I'm planning to insulate and then put purlins on the inside to attach some sort of panel-metal siding, T1-11, plywood...not sure yet. For between the purlins, I'm planning to put up Rockwool batts that should give me a R-23 insulation factor, however, what should I do between the exterior purlins? Foamboard would be the cheaper option, but should I be concerned with moisture build-up between the back of the exterior metal siding and the foam? Any tips would be greatly appreciated.