I’m in the middle of constructing a wood shop/building. I could not get the siding on this season so used a PPG deck stain with UV block on the exterior OSB. The interior is batt insulation and drywall. It is only heated as needed with a wood stove. During certain weather conditions – cold clear nights – there is frost on the exterior at the stud bays. What is happening and is it okay? Will this continue to happen to the siding on an unheated building?