# Pole Barn Walls insulation - Vapor barrier ?



## UpNorther (Oct 5, 2018)

Hi all, 
I'm in central Minnesota, so winters get cold. 
I'm just starting to insulate my existing pole barn. 
From the inside going out the layers are :

Steel paneling, kraft faced R19, 1 1/2 polystyrene, Steel paneling. 
No poly and no Tyvek.

Pole barn is already built with horizontal girts mounted on the outside of posts. Cost effective, its cheaper to install 1 1/2" polystyrene in between those girts. 
Then frame horizontal framing between posts and install kraft faced R19 horizontally. 

Kraft faced insulation serves as the vapor barrier, but personally I've never been a fan of it as compared to poly covering an entire wall.

My question is: What other steps should be taken to seal it from outside elements without making a double vapor barrier ? 
Between steel, kraft faced insulation, polystyrene, & steel again, I'm really thinking I shouldn't take more steps like taping polystyrene seams ?
If I knew then, I should have Tyvek'd outside before steel paneling went on.. 

Thanks


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## Bud9051 (Nov 11, 2015)

Hi upnorth and welcome to the forum.
Is the purpose of this insulation to make this space livable? How deep are the wall cavities?

With steel inside and outside you already have a double vapor barrier. The vapor barrier designation refers to how well moisture vapor will pass through a material, not concerned about passing around. Although air leakage will move a lot of moisture a vapor impermeable layer (such as steel) will provide a condensing surface.

Don't know enough about your building and its use to comment further.

Bud


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## UpNorther (Oct 5, 2018)

Hi Bud, thanks for your reply. 

The purpose of the pole barn is to have a workable shop space, with a section of it for a man cave. 
Winters here can hit 20-30 below zero, so up to a 100 degree temp difference between inside/outside can be common in January. 
Heat will be infloor slab, heated by natural gas boiler. 
Wall thickness is 7" (5 1/2" post plus additional 1 1/2 from girts), so my combo of R19 & 1 1/2 " styro fit nicely. 
I should have added in earlier post that pole barn steel sheeting has ribbing, so air does channel through it. Picture below. 

Where I'm at there are 3 common practices for insulating pole barns: 
1- tyvek on the inside of exterior steel panels, then spray foam 2-3" of closed cell foam. Then framing inside, and steel panels over. 
2- tyvek inside of exterior wall, spray 1" closed cell foam, frame wall, install fiberglass batts, then poly vapor barrier, then steel panels over. 
3- tyvek on the inside of exterior panels, frame inside, 6 mil poly vapor barrier. Then blow in fiberglass insulation between framing members. Then install interior steel paneling. 


Cost for 3" of closed cell foam & tyvek is $6,400 giving about R20 value. 
Cost for 1" of closed cell foam, tyvek, & batts is $3,400 giving about R25 value.
Cost for 7" blow in fiberglass insulation & tyvek is $1,300 giving about R26 value. 
Cost for my combination of polystyrene & batt insulation (no tyvek) is $2,000 giving about R29.

So it brings up the question, with air channeling between the ribbing on the steel panels, Should the 1 1/2" polystyrene be taped/sealed at the seams, or would it create a double vapor barrier between styro and kraft insulation?


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## Bud9051 (Nov 11, 2015)

Assuming zone 6 near Minneapolis (could be zone 7 farther north).
First question is, are you required to meet insulation codes with this building, ie permits and inspections? Since every area can choose what version of the codes they will require and even modify that you need to contact your local authority to determine your target minimums.

Having said that, regardless of codes you have a vapor barrier issue. In addition to the double vapor barrier I mentioned there is *guidance* specifying how thick a continuous layer of exterior must be over a 5.5" wall. Zone 6 shows R-11.25 for the rigid. Zone 7 shows R-15. But, those numbers are for continuous rigid and yours is not, which complicates the guidance and reduces the effective r-value.

You cite common practices but not code requirements. Since your approach is unique to your area the guidance you seek needs to come from local authorities. I would just be guessing.

Bud


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