I'm not going to go on and on about this...and I do respect everones ideas, but have you ever been in the attic and seen that black and gray mold? I'm sure that most of us has...well this was a result of no barrier. And improper venting. You can also see this on the uderside of a floor that has insulation, again it's from the lack of vapor barrier. I live here in Michigan and the humidity is no big problem. As we all know a good tight house leaks, and any good well built house thats is tight has a make up air system in it anyway, so the idea of to much moisture should never be a problem. Just as a ending note at any point you do not have a vapor barrier and the cold hits the warm you will get water....thats just the way it is, and things will rot. Again I respect everyones thought's but I had to have my final say.