Ok, I am going to try to explain and see if this is a good idea or a bad idea. Im to the point of my build of insulating the walls of my pole building. Heating will be radiant in floor. My original idea was to staple r21 to 2x4 purlins 2ft on center. (5.5" thickness). As i waiting for some funds i figured i would put some rigid foam 1.5" in back of the poles just for some extra insulation. (shown in pic) Now my question is. My wall depth is 8" from interior wall the the outside metal sheathing. Curious if it would be a good idea or beneficial to put 1.5" rigid foam insulation on the "outside" and then the r21 staples to the inside where I originally figured I would. This would leave 1" of dead space (air) in between the 2. (I have about 70% of the foam board I would need to do the job) Please give me some insight, not an insulation expert by any means. Do not want to have moisture or mold problems down the road.
