Need some vapor barrier and insulation advice

[ovrszd]

Maybe a rando, but that makes two of us saying it. I asked you for your source, but you did not address that request.

You write: "You want the vapor barrier next to the cold side so no warm moist air can condense on a cold wall." I'm confused with the identity of the "you" I have underlined. Vapor barrier should not be next to the cold side. Georgia and north, vapor barrier should be on the conditioned wall - meaning, the interior wall.

You write: "compresses it and loose all insulating value." All insulating value is not lost. It is reduced to the R value that insulation, properly "fluffed" without compression, would have had. There is no increase in R value for compressing insulation.

I agree about just putting 3" of foam, and not mess with the bats, but that introduces a whole different economic scenario, than what the OP was not considering.

We were typing at the same time...

My shop walls are 2x6 studs. Tyvek wrapped on the outside. Then sided with metal. R19 faced batts stapled between the studs. Then OSB on the inside. So,, I guess I kinda have two vapor barriers.

I'm North of Georgia by quite a bit.

 

[Have tractor did travel]

ovrszd Not as i see it. Tyvek lets moisture out, but not in - not a vapor barrier. Metal, is impervious to vapor transmission. But it requires special effort to seal joints (see post 9 "Permeance of Steel Roof Decks . . ." ) So no vapor barrier there.
Then, working from the inside of the outside wall, the R19 bats are faced - there's the first vapor barrier, and I presume you place the facing toward the "conditioned" side, meaning, toward the heated and cooled rooms of the house.
As long as you used unfaced OSB, OSB is not a vapor barrier

 

[ovrszd]

ovrszd Not as i see it. Tyvek lets moisture out, but not in - not a vapor barrier. Metal, is impervious to vapor transmission. But it requires special effort to seal joints (see post 9 "Permeance of Steel Roof Decks . . ." ) So no vapor barrier there.
Then, working from the inside of the outside wall, the R19 bats are faced - there's the first vapor barrier, and I presume you place the facing toward the "conditioned" side, meaning, toward the heated and cooled rooms of the house.
As long as you used unfaced OSB, OSB is not a vapor barrier

Tyvek is to prevent moisture from entering the wall cavity? So it is a barrier against condensation moisture under the metal entering the wall?

So I have a barrier on the outside of my wall substructure preventing moisture from entering the wall.

I have a barrier on the inside of the wall substructure preventing moisture from entering the wall.

If I were doing my shop again, I'd do it like my house and start with 2" spray foam. But as you mentioned, this adds cost.

My house and shop are easy to heat. And tight.

 

[Have tractor did travel]

Tyvek is to prevent moisture from entering the wall cavity? So it is a barrier against condensation moisture under the metal entering the wall?

So I have a barrier on the outside of my wall substructure preventing moisture from entering the wall.

I have a barrier on the inside of the wall substructure preventing moisture from entering the wall.

If I were doing my shop again, I'd do it like my house and start with 2" spray foam. But as you mentioned, this adds cost.

My house and shop are easy to heat. And tight.

Overszd:
"How does house wrap work? The unique nonwoven structure of Tyvek HomeWrap makes it breathable, allowing moisture vapor to pass through. This helps to promote drying in wall systems, to help prevent mold and water damage."
The above from a google search. In my words - Tyvek allows water vapor to pass. The metal siding keeps the rain out, the tyvek allows the water vapor out of the house, and then passes out through cracks and joints in the metal. The barrier on the inside of the wall substructure preventing moisture from entering the wall is good.
Everything else you write is good.

 

[Mtsoxfan]

Here is the sourse I used. Walk-Out Basement Wall Insulation
Closed cell ridgid insulation IS the vapor barrier. Canned spray foam completes the seal. And he is a contractor from my neck of the woods, that and what I read was good enough for me.

 

[Have tractor did travel]

Here is the sourse I used. Walk-Out Basement Wall Insulation
Closed cell ridgid insulation IS the vapor barrier. Canned spray foam completes the seal. And he is a contractor from my neck of the woods, that and what I read was good enough for me.

MTS Thanks for joining in. I found the source on Basement Wall Insulation to be good reference. We've been talking about insulating a pole barn - above grade. Everything changes. I agree "the closed cell rigid insulation is the vapor barrier". Above grade, the vapor barrier should be adjacent to the "conditioned" wall - i.e., the wall that faces the room(s) that are heated and air conditioned.

 

[ovrszd]

MTS Thanks for joining in. I found the source on Basement Wall Insulation to be good reference. We've been talking about insulating a pole barn - above grade. Everything changes. I agree "the closed cell rigid insulation is the vapor barrier". Above grade, the vapor barrier should be adjacent to the "conditioned" wall - i.e., the wall that faces the room(s) that are heated and air conditioned.

I understand the principle.

I've never saw a wall with any insulation, covered with spray foam. I've always saw the foam against the outside sheathing, whatever that might be.

 

[Snobdds]

Maybe a rando, but that makes two of us saying it. I asked you for your source, but you did not address that request.

You write: "You want the vapor barrier next to the cold side so no warm moist air can condense on a cold wall." I'm confused with the identity of the "you" I have underlined. Vapor barrier should not be next to the cold side. Georgia and north, vapor barrier should be on the conditioned wall - meaning, the interior wall.

You write: "compresses it and loose all insulating value." All insulating value is not lost. It is reduced to the R value that insulation, properly "fluffed" without compression, would have had. There is no increase in R value for compressing insulation.

I agree about just putting 3" of foam, and not mess with the bats, but that introduces a whole different economic scenario, than what the OP was not considering.

I think you're getting a bit confused here. You are steadfast that vapor barrier, no matter the type, needs to be next to the warm side. Which is true if you are using anything but foam. Closed cell foam is a completely different animal and you can't apply the old logic to this material. Foam needs to be next to the sheathing, that is how it was designed to be. It provides a vapor barrier, a thermal break, racking strength, and it basically glues the entire building envelope together. You are only getting one benefit, some r value, if you spray foam over batt insulation. Why give up the other huge benefits.

Now I know a lot of people, that are cost centric, say just spray one inch of foam and then put in batts to get to the proper R Value. Well, there is some water vapor that does permeate the batt insulation and travels to the foam, where it stops. However, things dry to dry and that vapor will eventually migrate back to the dry side of the envelope. I still think if you are going to use foam, just pony up a little bit more and get the full R value sprayed in and then it's all a moot point.

If you use foam, there needs to be fresh air movement. It needs more that people think too.

 

[Have tractor did travel]

I think you're getting a bit confused here. You are steadfast that vapor barrier, no matter the type, needs to be next to the warm side. Which is true if you are using anything but foam. Closed cell foam is a completely different animal and you can't apply the old logic to this material. Foam needs to be next to the sheathing, that is how it was designed to be. It provides a vapor barrier, a thermal break, racking strength, and it basically glues the entire building envelope together. You are only getting one benefit, some r value, if you spray foam over batt insulation. Why give up the other huge benefits.

Now I know a lot of people, that are cost centric, say just spray one inch of foam and then put in batts to get to the proper R Value. Well, there is some water vapor that does permeate the batt insulation and travels to the foam, where it stops. However, things dry to dry and that vapor will eventually migrate back to the dry side of the envelope. I still think if you are going to use foam, just pony up a little bit more and get the full R value sprayed in and then it's all a moot point.

If you use foam, there needs to be fresh air movement. It needs more that people think too.

Snobdds, In our exchange (post 27) I provided a link showing agreement with my position of spray foam over insulation; and asked you to provide substantiation for your position. Can you now do that ?

I agree, to a limited degree, with racking strength and 'glues the entire building ... together'. However, spray foam is not a building code requirement for houses meeting Cat 3 wind resistance (I don't know about 4 and 5), so while we have no disagreement over this point, the 'glue' and racking strength may have esoteric value, but no monetary value.

You mention "It provides a vapor barrier, a thermal break, racking strength, and it basically glues the entire building envelope together. You are only getting one benefit, some r value, if you spray foam over batt insulation. " I say applying the foam over the batts provides all of the values you ascribe, AND WITH THE VAPOR BARRIOR IN THE RIGHT LOCATION.

We also agree about the value of ponying up a little bit more for full R value and then there need be no concern over foam over, or foam before, batts.

 

[Snobdds]

Snobdds, In our exchange (post 27) I provided a link showing agreement with my position of spray foam over insulation; and asked you to provide substantiation for your position. Can you now do that ?

I agree, to a limited degree, with racking strength and 'glues the entire building ... together'. However, spray foam is not a building code requirement for houses meeting Cat 3 wind resistance (I don't know about 4 and 5), so while we have no disagreement over this point, the 'glue' and racking strength may have esoteric value, but no monetary value.

You mention "It provides a vapor barrier, a thermal break, racking strength, and it basically glues the entire building envelope together. You are only getting one benefit, some r value, if you spray foam over batt insulation. " I say applying the foam over the batts provides all of the values you ascribe, AND WITH THE VAPOR BARRIOR IN THE RIGHT LOCATION.

We also agree about the value of ponying up a little bit more for full R value and then there need be no concern over foam over, or foam before, batts.

I don't think you understand how the internet works. Everyone can find someone on the internet that backs any position out there. Substantiation on the internet is really non existent. Unless your google is broken, maybe seek out things that don't line up with your beliefs. You might just learn something new instead of insisting you know better than anyone.

You're right there is no code for gluing everything together with foam, but what you're missing is it's a value added thing, some will pay for a better than code build.

Where the line needs to drawn is when people give bad advice. Saying you can spray foam over batt insulation is bad advice and it should be pointed out. No good contractor sprays foam over batt insulation. And no, I'm not going to substantiate that...that is just known information in building.