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Insulation, Vapor Barrier, Air Barrier for Pole Barn Conversion

katesandy13 | Posted in Energy Efficiency and Durability on

I covet any and all advice/encouragement.

I am currently in analysis paralysis mode… Due to this mode, I am (literally) still living in a tent. I’m in zone 3a in Alabama. I have a 20×30 pole barn on a concrete slab that I am going to convert into a house, I’ll be adding a 15×30 addition that will have a crawlspace.  I want this to be as energy efficient as possible, I’d rather spend the money needed up front to do it right. It will be heated with a wood stove. I am struggling with all of the options- air sealing, vapor barriers, insulation, etc.  I was able to salvage lumber from another barn that took a hit. I have enough lumber to do 2×6 construction on the 30′ sides of the house but will have to do 2×4 construction on the 20′ sides of the house.

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  1. Expert Member
    BILL WICHERS | | #1

    It is notoriously difficult to do a good job insulating and air sealing a pole barn. Many resort to what I would call "extreme methods" and spray foam EVERYTHING. Keep that in mind, as you are going to get other replies that will all be something along the lines of saying that "as energy efficient as possible" and "pole barn" tend to be contradictions.

    The new build is much simpler, assuming you will be doing normal stick frame construction (stud walls, not poles). I would normally use mineral wool batts in the walls, exterior polyiso on the outside of the studwalls, and blown cellulose on the floor of a vented attic. I would use XPS on the exterior of the foundation for the crawlspace, and put a liner down inside to "encapsulate" the crawl space. This would get you a reasonably well insulated shell, you can get good air sealing by being careful and using caulk and canned foam in the right places as detailed in various articles on GBA.

    The pole barn part is a problem. Are planning to frame new walls inside the pole barn? Are you planning to keep a 'rustic' look, leaving the poles exposed? What your plans are here will help to determine what might be the easiest way to go to get you what you want.

    If you're getting some of the terminology mixed up, just remember this:
    INSULATION slows the flow of heat from one side to the other. It's usually something like fiberglass batts, but it can also be cellulose or even rigid foam board (EPS, Polyiso, etc.). Insulation is all about keeping things warm when it's cold out, or cold when it's hot out. Insulation isn't intended to block the flow of air or moisture, although some kinds do.

    VAPOR BARRIERS are intended to BLOCK the flow of moisture. this means they keep humidity out (or in) compared to the "other side" of the barrier. Vapor barriers are usually polyethylene sheet, but can also be the foil facer on a sheet of polyiso. Vapor barriers are usually avoided in many construction assemblies. Note that vapor RETARDERS slow or reduce the flow of moisture, but don't stop it completely, so they aren't the same as a vapor BARRIER, even though they often look the same.

    AIR BARRIERS are intended to block the flow of air through an assembly, which help with efficiency by not letting your heated (or air conditioned) air escape. Air barriers are usually drywall, sometimes plywood or OSB, and sometimes rigid foam board. Air barriers are also needed over batt-type insulation to help it perform to spec.

    Some things can act as multiple of those things at the same time. Foil faced polyiso, for example, is insulation (polyiso), a vapor barrier (the foil facer), and an air barrier (the entire sheet of material), all at the same time. We can help you use the best material for the application here, and there are a lot of articles that explain why you should use what, where.


  2. katesandy13 | | #2

    Thanks so much for the thoughtful response. To answer your question: Yes, I am framing new stud walls in the pole barn.

  3. DC_Contrarian_ | | #3

    So you already have the pole barn? And you have a good amount of 2x4 and 2x6 lumber? I'm thinking basically a house within a house -- the pole barn is a skin that keeps the weather out, inside of it you build a shell that is your air barrier, insulation and vapor barrier. In Alabama I would think you're cooling dominant -- you cool more than you heat -- which means you want the vapor barrier on the exterior of the walls so they can dry to the interior.

    I don't know what version of the energy code you're under, but under the 2021 version you need R-49 for the ceiling, nothing on the slab. For the walls you have to do either R-20 of fluff, or R-13 of fluff and R-5 of foam board, or R-15 of foam. R-20 is a 2x6 wall filled with batts or blown in, R-13 is a 2x4. R-5 of foam board is 1" of polyiso or 1.5" of polystyrene.

    I would go with 2x6 walls all the way round because it makes the insulation simpler -- just fiberglass batts with the paper on the outside. You'd have to buy about 15 10' 2x6's for each wall, they are about 10 bucks each these days but that's going to be cheaper and less work than adding exterior foam to 2x4. You can space the studs 24" which saves a bit. Then drywall on the interior for your air barrier.

    I would paint the floor with a vapor barrier paint unless you are sure there is a vapor barrier under the concrete.

    For the ceiling you need 12" of insulation. If you run a wall down the center of the building your ceiling spans slightly less than 10', you can do that with a 2x6. Bigger spans may be nicer but the lumber gets a lot more expensive. To put 12" of insulation on 2x6 joists your best bet is loose blown insulation. You want the space above the insulation to be freely ventilated to the outdoors -- but protected with screens from pests. The drywall ceiling will be your air barrier, you want to make every effort to make it as air-tight as possible. Try to resist anyone who wants to put air conditioning equipment in that attic space.

    The addition needs siding and a roof. The crawl space is probably a discussion of its own, I recommend this article:

  4. MartinHolladay | | #4

    You might want to read this article: "Insulating a Pole Barn."

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