Someone please help me! Plan to finish & condition our 1930s attic space into bedrooms, bath, and hobby room. We live in north central Montana, where winters are severe. I have people telling me it is fine to use spray foam to completely seal off the space from the outside (we are not re-doing the roof, which is shingled). My gut tells me that the house needs to breathe and I'm very scared about letting someone seal it off. Can anyone tell me if this has proven to be okay to do? All the research that's out there is very confusing, and I can't find anything related to our particular climate. We're short on vertical space up there, so the spray foam holds advantages from that point of view. House is wood frame/brick exterior. Thanks so much for any input!!!