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Newbie: insulating shop in a barn

user-607035 | Posted in Energy Efficiency and Durability on

Hi.

Thanks all for reading. I’ve read a lot about insulation and vapor barriers, and think I am more confused before reading about it at all! Hopefully some of you can help me understand the best plan.

I want to build out an existing pole barn shell. Roof currently is 1″ polyiso foam, 1/2″ OSB, roof vapor barrier and steel. Walls are from inside to outside 1/2″ OSB, house wrap, and T-111. Barn located in mountains of northern NM, a heating environment with general low outside humidity.

Several questions.
To insulate the exterior walls: should the order fro the current OSB layer, be faced fiberglass insulation, with face to inside, then vapor barrier, then sheetrock?

Interior partitions: I want to build a self-contained 20×30 room within the pole barn to house a wood shop. I want that to be well-insulated so I can easily heat the space. Should the interior partitions have vapor barrier on the heated side? Any other considerations?

Interior loft: There is room for a loft above the future insulated wood shop. If I entirely close off that area of the loft, and insulate it will I have problems with moisture from the steel roof? Or will the existing roof insulation be adequate? I will insulate the floor between the two spaces since the loft will like be unfinished for a season or two after the wood shop is done. Should I long-term plan on adding real roof insulation to the loft if I want to use it for an office of guest room? And if YES which seems likely, when you already have 1″ of polyiso foam, can you add fiberglass on its interior–vapor barrier, ventilation?

Thanks in advance for your help.

Rob

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Replies

  1. Expert Member
    Peter Yost | | #1

    Hi Rob -

    We worry about moisture in the following order: bulk water (rain leaks); capillary water (wicking); air (moisture carried by air leakage); diffusion (vapor moving by gradient).

    In your assemblies, make sure you worry in this order: get all flashings connected to your WRB; decouple soil from building elements (cap breaks: non-porous materials OR minimum 3/8-inch gaps); continuous air control layer.

    In your climate, worry less about vapor retarders and more about continuous air barrier. Don't ignore household moisture sources (https://www.greenbuildingadvisor.com/article/moisture-sources-relative-humidity-and-mold), but not unusual for air leaks to move 100 times more moisture than vapor by diffusion.

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