Advice on WRB for a Pole Barn
I am getting ready to have a pole barn built. The loft of the structure is going to be heated space, but I’d like to build the main level good enough that I can convert it to conditioned space in the future if needed. I will be putting insulation under the slab floor, and have also specified that I’d like a WRB during construction in the contract. I did not have the contractor install sheathing; I was planning on sheathing on the interior side of the girts with OSB and taping the seams myself with a good tape when I do the work to finish the loft area (the contractor is leaving the loft unfinished).
My question is regarding the wrb — the contractor is intending on using tyvek for the WRB, but I was wondering if I should ask (and pay) for a better product like a blueskin peel & stick? I don’t know if it can be installed over girts instead of sheathing, but I’d assume that it would be a better result than tyvek nonetheless.
Thanks in advance for the advice.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I would look at commercial Tyvek. Much stronger than the regular homewrap and would take a lot more abuse.
Peel and stick in this case won't work as there isn't anything to adhere it to. You only really need that for things like t&g or board sheathing that are hard to air seal any other way.
Make sure they don't include bubble wrap anywhere you want to finish down the road. Exterior vapor barriers are a bad idea in anything but the warmest of climates.
Since you'll be finishing the upper section, make sure there is an easy way to add soffit to ridge venting (if your purlins are at 90 deg to slope, add in sleepers above them to space the roof deck up). Without proper venting your only good option for roof insulation is spray foam which gets expensive.
What are you doing for siding?
Pole barns don't convert well to finished space. Joe Lstiburek has an article where he talks about the four layers of an exterior wall -- weather, air, vapor and insulation -- and how on your plans you should be able to trace the path of each layer around the entire building without lifting your pencil off of the paper. Pole barns typically have just a one-layer wall, for weather. Adding the other three layers after the building is built is tricky. Difficulty usually comes where surfaces meet, like wall meeting wall or wall meeting roof.
Looking at the reply from Akos and DCContrarian -- I didn't read the article by Joe Lstiburek, but I did read the article on GBA by Martin Holladay regarding the same subject. The siding is going to just be metal siding.
Would it be very worth my wallet's while to just have the contractor install plywood sheathing then on the exterior side of the girts, before siding, and then applying the WRB to that instead of sheathing afterwards from the interior side? If I do that, would a peel-and-stick be a superior option in that case?
The way I see it a pole building is designed with the single goal of providing dry floor space at the lowest possible cost per square foot. That makes for a great place to park a tractor but when you start trying to heat and cool the space all the compromises made to keep down the cost of initial of construction eat you alive.
If the plan going in is to build conditioned space then build a real building and not a shed and then attempt at converting it into a building.
If you are stuck on a pole building then plan on building a tight well insulated building inside without a roof.
Did you see these articles?
https://www.greenbuildingadvisor.com/article/insulating-pole-barn
https://www.greenbuildingadvisor.com/article/insulating-a-metal-building
I am sorry if I sound a little grumpy but this question gets asked about every 14 days or so generally after it has been built, how I make a silk purse out of my sow’s ear for a song.
Walta
Walta --
You actually said it much nicer than I was going to. I was going to say pole barns have three design criteria -- cheap, cheap and cheap.
To reimhagen (the original poster) --
If your plan is to convert the barn to conditioned space in the future, you should plan that out now while it just involves changing lines on a piece of paper. I think you will find, as Walta suggests, that the framing of a pole barn is so ill-suited to a four-layer wall that you basically end up building a building-within-a-building.
I would also price out a building where the walls are 2x6 on 24" centers and the roof has trusses that can hold a drywall or plywood ceiling and a couple feet of loose insulation. My guess is that's the cheapest construction that lends itself to a truly insulated building.
I'll add that in the places I am most familiar with an inspected building cannot have wood structural members below ground, even a deck has to be on concrete piers. I realize this is regional.
To the original question, for a pole barn metal siding is all you need for a WRB.
My neighbor is building a pole barn he intends to heat. He has applied closed cell spray foam to the back of the metal siding and intends to frame an interior wall with fiberglass insulation. The thickness of the foam and interior fiberglass would depend on the climate zone. The posts bear on concrete piers.