Pole barn build: Condensation barrier and house wrap??

[VtecGSR95]

Good afternoon all!

I am about to start the build on my 40x64x16 personal shop. I was getting quotes on spray foam in advance......and the local company who has an excellent reputation told me that if I am planning to do 5" open cell spray foam, house wrap is a waste of money, unless I am concerned about having to replace a panel someday. They went on to say they will blow in enough cellulose in the ceiling to achieve R-49 value, and then said with my vented soffit and ridge vent, there was no reason to spend the money on condensation barrier in the rook panels.

Now this is huge for me....as the house wrap labor and materials, as well as the added cost of the "drip stop" could pay for my ceiling insulation! But I am concerned about having nothing there......but the salesman said the venting I will have with my 2' overhang and vented soffit and vented ridge, the temperature variance above the ceiling insulation would be so little that its a waste of money.

Can anyone help me on this? I want to make the right decision.....but don't wanna spend extra money if I dont need to!

 

[dcg9381]

The issue I can't speak to is geography. In Texas, these buildings are not wrapped at all. And even air conditioned (like mine) and in humid climates, I have no issues with condensation.

I'd go look at some "barndominiums" in your area and/or visit the nearby general aviation airports. Airports will likely have this type of construction... Ask and see what's actually working.

The other deviation (here) is the these buildings with HVAC are NOT vented - part of foam is providing a sealed envelope. The soffits and ridge vents that are part of typical steel building construction are sealed on my building.

I like the idea of blowing in cellulose as additional insulation.. Sounds like you're framing?

 

[kbs2244]

"house wrap" under the outside paneling is a liquid water barrier to water soaking into the wall

 

[VtecGSR95]

The issue I can't speak to is geography. In Texas, these buildings are not wrapped at all. And even air conditioned (like mine) and in humid climates, I have no issues with condensation.

I'd go look at some "barndominiums" in your area and/or visit the nearby general aviation airports. Airports will likely have this type of construction... Ask and see what's actually working.

The other deviation (here) is the these buildings with HVAC are NOT vented - part of foam is providing a sealed envelope. The soffits and ridge vents that are part of typical steel building construction are sealed on my building.

I like the idea of blowing in cellulose as additional insulation.. Sounds like you're framing?

Guess I should clarify.......5" open cell foam in walls only, then blown in cellulose in ceilings. The insulation guys will make all the provisions to ensure the soffit is able to vent above all the blown in cellulose.

I am only planning to add girts to the walls and sheet metal the inside with standard white metal, same for the ceiling. I will heat it some on the winter, but no a/c planned as of now......maybe in a few years I might try adding something small to take the edge off.

 

[VtecGSR95]

"house wrap" under the outside paneling is a liquid water barrier to water soaking into the wall

I thought it was more of a wind barrier than moisture? And from what I've read and seen, it doesn't appear that the foam would absorb moisture unless it was laid horizontally, and water allowed to sit on it for a period of time? I figured on walls, the foam would act similar to a house wrap......seal all potential air leaks, as well as stop moisture from penetrating?

 

[purediesel]

House wrap is a water barrier not a vapor barrier. It will stop water but not water vapor, so therefore it breathes. I put it on my building as well as an osb roof. I wanted the best resistance to any moisture in the building. I like your plan for the insulation, but I'd add the house wrap since its really not all that much. I will add that you should look into what trusses they are planning for your building. You need to look at what the chords are rated for for live and dead loads. If the trusses aren't designed for a ceiling you wont be able to safely install one or you just wont be able to do that much insulation. You'll want around 5psf dead load on your bottom chord so ask your builder what they have planned and to see the engineered truss sheet.

 

[VtecGSR95]

House wrap is a water barrier not a vapor barrier. It will stop water but not water vapor, so therefore it breathes. I put it on my building as well as an osb roof. I wanted the best resistance to any moisture in the building. I like your plan for the insulation, but I'd add the house wrap since its really not all that much. I will add that you should look into what trusses they are planning for your building. You need to look at what the chords are rated for for live and dead loads. If the trusses aren't designed for a ceiling you wont be able to safely install one or you just wont be able to do that much insulation. You'll want around 5psf dead load on your bottom chord so ask your builder what they have planned and to see the engineered truss sheet.

The trusses are 2x8 top and bottom chords. Didnt look at the actual load specs, but they know I am planning to finish the ceiling, and they're 8' on center.

 

[purediesel]

The trusses are 2x8 top and bottom chords. Didnt look at the actual load specs, but they know I am planning to finish the ceiling, and they're 8' on center.

My builder knew also and there was still a mistake. Ask for the sheets