Barndo Spray Foam?

[Biggs]

I'm building a barndo in Temple. I've got all interior wall insulation figured out but a still waffling on what to do on the exterior walls and roofdeck.
My initial plan was 2" closed cell on all exterior walls and 5.5" open cell on the roof deck but...
2" closed cell on all exterior walls? Too much?
1" closed cell plus 3" open cell on all exterior walls?
Is open cell ok on shop walls?
Cost per sq ft you’ve been seeing?
What advice for Spray Foaming a Barndo?

[Mike D]

Why would you do different types of foam?


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[bloodtrailer28]

We used open cell on walls and roof...love it. Not sure why you would use different types of foam mixed together?

We went 6 inches on the exterior walls and pushing 7-8 inches on the roof.

[bowtec8]

I built our barndo and went 1” closed cell and 5 inches of open cell on top of closed cell. It’s awesome. I can heat our whole house with just the fireplace. In the summer I’ve yet to have an electric bill over $200.

[Buckshot4900]

I sprayed under roof and exterior walls with full 1” closed cell. Only drawback is moisture retention. I use an automatic dehumidifier that pumps in the drain and it works perfect to store leather goods.

In my house is sprayed 2” closed cell under the roof and went with 5” open cell in the exterior walls just for ventilation purposes.
No attic insulation due to using 3/4” tongue and groove ceilings.


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[Biggs]

Why would you do different types of foam?


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My understanding is Price vs R-value I guess.
2” closed cell is R14
1” closed and 3 inch open is R17 and cheaper.

[Bureau2]

Go with either one, you’ll be glad you did! Good luck on the build!

[RdRdrFan]

Your plan sounds solid.

Why two types? Open cell can hold water and rust from the inside. Closed cell won’t but the R-value is pretty weak. Open cell over closed cell is the best of both worlds.

[bloodtrailer28]

Your plan sounds solid.

Why two types? Open cell can hold water and rust from the inside. Closed cell won’t but the R-value is pretty weak. Open cell over closed cell is the best of both worlds.

Have never heard of them using 2 types of foam together. Thanks for the info.

[ken800]

Y'all feel free to tell me I'm wrong but I believe you have the open/closed cell retention issue backwards. My last house had closed cell in the 2x4 cavities and about 6" of open cell in the attic. Open cell can sorta act like a sponge and soak up water whereas closed cell doesn't. I had no end of problems with my attic and humidity/mold and ended up having to put a dehumidifier in the attic and run it full time.

If you read the technical bulletins almost all will tell you that you have to add an additional vapor barrier in colder climates to prevent roof rot. Obviously we aren't in the coldest climates, but metal buildings sweat profusely in extreme weather changes as the metal changes temperature much more quickly than wood. ANY air leak will sweat. If I were insulating a metal building with foam, I'd follow zone 5+ guidelines and use a level 2 vapor barrier if I was doing open-cell or just stick with closed cell.

https://www.dolphin-insulation.com/blog/roof-rot-roulette-not-worth-the-risk/

Here's an example from New England. Yes, I know that's way north but they have codes there that required the vapor barrier with open-cell...

Here's a more technical article from the home inspectors association. Again, they specifically recommend a vapor barrier with open-cell in colder climates.

https://www.nachi.org/inspecting-spray-foam-insulation-under-roof-sheathing.htm

[macoop]

I just spray foamed a metal building that is really a barndo. I put 2 inches of closed on the roof and one inch on the walls. Then he came back and put 3 inches of open on top of the closed cell in the walls. The open adds more R value and also serves as a sound barrier.

[Mike D]

Barndo Spray Foam?

That’s why I was asking. If you are spraying open cell directly
On the metal you are asking for trouble IMO.

If you aren’t planning to wood sheath the walls and ceiling I would definitely spray closed cell directly in the metal and then top with open cell.

I can tell you that 2” of closed cell on my well house kept my well from freezing even through we got down to -3° last well. I do not have any type of heat source in there either.

If it were my build I’d probably spray 1” closed and top with enough open cell to fill your wall stud cavity. On the roof I’d probably do 2” if closed cell and top with 3-4” of open.

If you plan to install wood sheathing & decking I would do all open cell.

I’m really not familiar with what traditional practices are used on barndo construction.

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[Keith]

Well, I learned something new today.

[Txarrowhunter]

I’m currently building a 3064sqft barndo and most guys that I’ve received quotes from that have sprayed many barndos have told me that if I don’t have a moisture barrier that I need 1” closed cell directly to the metal before doing the open cell. Having said that in north tx a 40x60 with 14’ sidewalls and 5/12 roofpitch with 1” closed cell on all exterior walls and roofdeck with 4” open cell on walls and 6” open cell on roof deck is $14500.

[BrianL]

I chose roll insulation on building and open cell in living area. I really wish I had done the closed cell/open cell instead. The closed cell really gives the building support and closes it up tight. Go with your original plan.