Question on attic insulation

[swampthang]

Planning on haveing a pole barn build soon and was going to insulate and finish thi inside myself. Im no carpenter so I learn by surfing the web and asking people. lots of heat and humidity in the summer and cold in the winter. I planned on putting a vapor barrier behind the tin that will be the ceiling of the garage then insulation. I was told that I also need a vapor under the actual tin that is the the outside roof as well, because the air in the attic will be warmer then the outside air. Is this correct or was I miss lead?

 

[tfinniii]

The roof sheathing doesn't need vapor barrier ,but should have adequate ventilation and the ceiling should have vapor barrier. If you have sealed wall surface with good paint that shouldn't need vapor barrier,but it would be good to wrap building with Tyvek material under siding.

 

[Highbeam]

I just did this. 6 mil plastic under metal ceiling and then blew 15" of cellulose on top. The attic is vented and there should be no warm or humid air from the shop up there. No VB on the roof.

House wrap under the metal siding and then faced batts on the walls behind OSB.