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Insulation question

homer14 | Posted in Energy Efficiency and Durability on

Hello. This site was recommended to me on another forum regarding some insulation questions. I have a pole barn and i plan on heating it. Right now im preparing to insulate it.

[So far]
42x40x14, vinyl sided, shingle roof, cement floor. Two 12×10 insulated doors, one 8×7 instlated door, 1 insulated service door, 4 3×3 windows, 2 4×4 windows upstairs. loft upstairs in middle. This is in climate zone 5, ann arbor michigan.

I want to have osb internally, not worried about pretty drywall.

The osb was wrapped on the outside with tyvek and then vinyl sided. So outside to in goes vinyl/tyvek/osb currently. Then there are the 6×6 poles. And at the top of the poles there are some 2×6 pieces too which are adding support for something (trusses? headers? i have to go look again).

I am not sure what the proper order of vinyl, tyvek (too late, its on), osb, , , osb inside for the walls. For example should i foam board it, then fiberglass batt it?

then what about the ceiling, which has a loft down the middle. plastic stapled, then osb or sheet metal, then spray insulation on top?

then i next i need to figure out the loft walls and whether or not to build a celing on it and spray above it or just do tricks against the roof itself?

i am mainly concerned about the walls right now but shared the rest of the details because i suppose they could make a difference in the overall plan.

thanks for your help. i plan on taking pics tomorrow and maybe those will help too. ill put them on here if i can.

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  1. GBA Editor
    Martin Holladay | | #1

    Pole barns can be difficult to insulate because (a) they often lack an exterior air barrier, and (b) they don't usually have studs to support the interior finish material.

    Your tasks include:

    1. Taking steps to seal air leaks in the OSB wall sheathing that has been installed on your barn. You'll be working from the interior. You'll probably want to use a lot of high-quality tape (Zip System tape or Siga Wigluv tape) and canned spray foam for this task.

    2. Next, you'll want to decide whether you will be installing studs to support your interior wall finish. If you will, you may want to install a continuous layer of rigid foam between the interior surface of your OSB wall sheathing and your studs. For more information on how thick this rigid foam layer needs to be, see Calculating the Minimum Thickness of Rigid Foam Sheathing. (Although the article talks about rigid foam installed on the exterior side of the wall sheathing, the same minimum thickness rules apply when the rigid foam is installed between the exterior sheathing and the studs.)

    3. You'll need to choose some type of fluffy insulation to install between the studs -- probably dense-packed cellulose, mineral wool batts, or fiberglass batts.

    4. When installing your interior finish material (OSB or drywall), remember to pay attention to airtightness at all seams and penetrations.

  2. homer14 | | #2

    Thanks. there is a tyvek type of wrap on the outside of the osb between the vinyl siding and the osb. Does this not act as enough air leak barrier?

    I've read that air is good to some degree between insulation and wall for moisture control or is that incorrect?

    attached some photos of what im working with.

    thanks for your help.

  3. GBA Editor
    Martin Holladay | | #3

    Q. "There is a Tyvek type of wrap on the outside of the OSB between the vinyl siding and the OSB. Does this not act as enough air leak barrier?"

    A. I think that you are confusing water-resistive barriers (products like Tyvek) and air barriers.

    Here is a link to an article with more information on air barriers:
    Questions and Answers About Air Barriers.

    Here is a link to an article with more information on water-resistive barriers (WRBs):
    All About Water-Resistive Barriers.

    Q. "I've read that air is good to some degree between insulation and wall for moisture control -- or is that incorrect?"

    A. In general, the only location where you want an air gap in your wall is between the back side of your siding and the exterior side of your water-resistive barrier (WRB). This type of air gap is called a rainscreen gap.

    Here is a link to an article on rainscreen gaps: All About Rainscreens.

    Elsewhere in your wall assembly, air gaps or ventilation channels are almost always a bad idea. However, in the case of a pole barn retrofit like the one you are facing, it wouldn't hurt to have an air gap between the interior side of your OSB sheathing and some type of air barrier material. (See my next comment for more information on your options for dealing with the gaps between the horizontal 2x4s that your OSB is nailed to.)

    In your case, you have installed vinyl siding, which already incorporates an air gap. (The profile of vinyl siding creates its own air gap behind the siding.) So you don't need an additional air gap in your wall.

  4. GBA Editor
    Martin Holladay | | #4

    The horizontal 2x4s on the interior side of your OSB complicate your plan to insulate.

    One option is to try to create an air barrier on the interior side of the horizontal 2x4s -- perhaps with a layer of taped rigid foam, or perhaps with a layer of housewrap. Then you could install a stud wall on the interior side of your new air barrier.

    Another option would be to fill the 1.5-inch-deep spaces between the horizontal 2x4s with 1.5-inch-thick pieces of rigid foam. If you go this route, you will want to install the rigid foam with attention to airtightness -- which means that you'll need to seal the perimeter of each rectangle of rigid foam with caulk, canned spray foam, or high-quality tape.

    A 1.5-inch-thick layer of rigid foam would be enough to keep you out of trouble if you build a 2x4 wall on the interior side of the rigid foam in your climate zone (Zone 5), but it might not be thick enough if you decide to build a 2x6 wall. For more information on this issue, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

  5. homer14 | | #5

    Thanks. I read some of your links. My tyvek is taped at any seams but its been stapled like crazy so i suppose that breaks the air barrier potential there.

    Could i put rigid foam between the 2x4 girts, and seal the gaps of the foam, then put insulation batts of some kind (the ones with a paper side) horizontally between some extra 2x4 girts i will need to put up to nail osb to?

    note as you see in my pics, i have to fur out the poles a well with 2x6 due to how the headers are supported, unless i could remove those 2x6 pieces and replace them with osb since the headers do have the heavy duty structural screws. im mentioning this because i dont know how tight the fiberglass bats will have to be against the foam board if i did foam board first, or if the tightness doesnt matter much within a 0-1.5 inch?

  6. GBA Editor
    Martin Holladay | | #6

    There are lots of ways to do this, and the choice on how to proceed is ultimately yours.

    In general, more insulation is better than less insulation.

    One way to proceed might be called the "all foam approach." Install two or more layers of continuous rigid foam on the interior side of the horizontal 2x4s, staggering the seams of the rigid foam. All seams should be taped. Then attach a layer of drywall with long screws that extend through the foam to the horizontal 2x4s.

    The main disadvantage of this approach is that you don't have a cavity for running your wiring.

    Another approach is to choose which part of your framing establishes the innermost surface -- it looks to me like that would be the inner surface of the horizontal 2x6 that your roof trusses bear on -- and frame up a stud wall so that the inside edge of the studs lines up with that innermost surface. Then install InsulWeb on the studs and fill the entire deep cavity with dense-packed insulation. (You'd need a skilled cellulose installer if you go this route, to be sure that you get the needed density.)

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