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I had a new pole barn just recently built. The contractors put the steel roof on with no underlayment whatsoever directly on the purlings. I was not informed however I do take responsibility for this. My question is would it be financially feasible to have the roof taken off and then install underlayment? Or is there another alternative? The building 40 by 60 will have five and a half inches open cell in the walls. The ceiling will be sheet metal as well with a moisture barrier and adequate blown insulation. If the ceiling and the walls are completely sealed can I get away with leaving the roof deck bare?
New metal roof over purlins no vapor barrier
2/22/2020
Or copy this URL: https://www.metalroofing.com/spirit/comment/24811/find/Thanks for your question. Underlayment draped over purlins on pole barns have their limitations and are not really a good method of condensation / moisture control. So, all is not lost! I think there are some good solutions here. May I ask what the barn will be used for? Animal confinement? Just trying to gauge how much moisture will be inside of it. Also, where are you located?
Isaiah Industries, Inc.
2/22/2020
Or copy this URL: https://www.metalroofing.com/spirit/comment/24812/find/Two-thirds of the building are truck stalls there will be an interior wall built as well and that one third of the building will be heated as a workshop. The intent is in floor heating.
New metal roof over purlins no vapor barrier
2/22/2020
Or copy this URL: https://www.metalroofing.com/spirit/comment/24813/find/By "moisture barrier" behind the ceilings, if you mean a complete vapor barrier such as polyethylene, I really think you will be fine. You should not have exceptionally high moisture levels inside the building and that is helpful. If you ever needed to, you could add gable vents pretty easily at the peak in the opposing gables and that would probably carry out any moisture that does end up in the attic cavity. It would also help carry out summer heat.
Isaiah Industries, Inc.
2/22/2020
Or copy this URL: https://www.metalroofing.com/spirit/comment/24814/find/Todd thank you for your reply. To answer the restof Your question I am located in northeast lower Michigan :-)
New metal roof over purlins no vapor barrier
2/22/2020
Or copy this URL: https://www.metalroofing.com/spirit/comment/24815/find/You are in an area prone to condensation, especially spring and fall. I am still comfortable with what you plan to do though. Please call me if you ever run into any issues -- 1-800-543-8938 ext. 201. (If you were in Arizona, I'd of course be saying "rest easy, my friend, no worries.")
Isaiah Industries, Inc.
2/22/2020
Or copy this URL: https://www.metalroofing.com/spirit/comment/24816/find/