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Pole barn — ceiling vapor barrier?

James Williamson | Posted in General Questions on

I live in Alaska.. far northern Zone 7 probably zone 8. I have a pole barn that has metal siding and a metal roof on large wooden rafters. Shop/Barn is 45x50x14 and 8/12 pitch with stud walls and lathe is currently in place for the ceiling. The attic area as you can see is quite large due to the size and pitch of the roof
I am thinking about using metal interior panels as the ceiling (basically metal roofing without the UV paint protection) as opposed to sheet rock.

Question:

If i use the metal panels is a plastic vapor barrier needed. If the answer is no then what is the recommendation to seal the laps to ensure air tight seal and how much of a lap is needed?

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    James,
    Every insulated ceiling needs an air barrier. This air barrier is more important than the need for a vapor barrier -- although in your climate, an interior vapor barrier is also necessary.

    Steel panels are an excellent vapor barrier. However, they are a lousy air barrier.

    The best way to create a ceiling air barrier is with taped drywall. You could always install steel panels on the interior side of the drywall if you like the look or durability of steel panels.

    If you really don't want to install taped drywall, you need to come up with another durable air barrier -- perhaps OSB with taped seams. You could install a durable European membrane from 475 High Performance Building Products, but all of the fastener penetrations from the steel panel installation might compromise the air barrier.

    Whatever you do, don't use polyethylene as an air barrier. It's hard to seal the polyethylene seams, and the fastener penetrations (and job-site damage) will make it worthless.

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