I am staring at an empty 8.5" space in my garage walls with steel siding on the outside screwed onto 1.5" purlins attached to a 6x6 pole. I also have 1.5" perlins on the inside wall to nail my osb onto. I am thinking of stapling rolled 6" backed fiberglas on the inside perlins and then covering with 1/2" osb. This will give me a couple of inches clearance between the steel and th insulation. The siding is ribbed, so moisture can run off the steel. Since I am using backed insulation, will I need to add an additional vapor barrier before installing my OSB? I will be heating with a vented propane hanging wall heater.
