Open or closed cell foam

Geo-TH,In

Well-known Member
I called around and many insultors recommend open cell foam on metal roof.

Then I ran across this article.

An open-cell foam (about 0.5-pound density) is the most cost-effective way to insulate, but any opening over 1/16" could cause the foam to expand out onto the roof. It would be better to use a closed-cell (2-pound density) foam because it doesn't expand as much as open-cell and is more likely to fill voids but not go through them. In our neck of the woods, closed-cell foam costs about 56% more than open-cell.

Closed-cell achieves about twice the R-value per inch (open being 3.5 and closed being 6-7), but the density is 4 times higher and therefore you are using a lot more material to cover the same area. Closed-cell foam also contributes additional rigidity to the roof (while remembering our minimum safety assumption). Closed-cell foam is a vapor retarder, while open-cell is more vapor-permeable. This is important because you do not want water vapor within the foam condensing at the juncture where it contacts the metal.

I want a vapor barrier, so I'm leaning towards closed cell.
 
I also recommend closed cell. If you put on 1/2 as much the cost would be "comparableish" and it wiuld have more insulation value. In Terre Haute, putting R6 on the roof will assist in keeping it cool, and warmer in the fall/winter if you heat it, or a portion of it. Jim
 
For someone who totally railed on me and others in 2016 about how useless metal roofs were and how you would never have one, sure sounds like your going with a metal roof.
 
It sounds like an expensive experiment to me.

Things may have changed, but the metal manufacturers used to offer a warranty on their product if you followed their installation recommendations.
 
Only my opinion and observation threw personal testing with different products in my yard.
Metal will sweat. Nothing you can do about it except control the climate.
And all ventilation does in bring in more moisture from the out side.

Metal does the same thing as your car windshield does.
It radiates heat to the night sky more than the air around it.
That is why your windshield will frost over with ice when the temperature is above freezing.
So when you are so close to the dew point as we are this small temperature change will cause the metal to sweat.

Open cell foam insulation is the water based stuff you were asking about yesterday.
It has open cells so it will absorb water just like fiberglass insulation will.
Tyvek and tar paper are not vapor barriers. Water will go threw them.
That is how the moisture in a house wall gets out threw the Tyvek.

Close cell foam is just that. Closed cells.
It will not absorb water.
So it needs to be put on a dry surface to stick.
Any condensation that forms on the metal will be trapped there.
Once the temperature rises the condensation will revert back to a vapor.
Hopefully the closed cell was put on with very few air pockets during low humidity conditions to reduce this trapped moisture.

My solution was to put a thick rubber water proof tarp between the rafters and metal.
Any condensation that forms on the metal can not drip in the barn because of this.
 
A shingle roof would solve George's dilemma. I seem to remember that he is the same age as me. He would be 90 years old by the time the shingles would need replacement.
 
Times are changing.
Roofer doesn't like the idea of putting osb and shingles on a 14ft building.
Condensation hasn't changed.
BIL has foam on his 14 foot metal roof.
So this old dog may have found a solution to condensation.
 
Spray foam has answered my concerns of fastener failure, metal blowing off and condensation. The foam will act like glue. Quiter when it rains. Possible less hail damage. Cooler in summer. And CHEAPER.
Should last my lifetime.
 
That close cell insulation sprayed directly on a dry metal roof will not trap any moisture at all. It sticks like paint would and there is no air pockets. Then the bottom seals itself. I had to put in a chimney on one of the roofs we had spray foamed. I had the piece I had cut out to fool with. I tried getting the foam off that piece. It was about impossible. You can not scrap it off a very wide section. I finally took a hand saw and cut across right beside the metal. Then with the foam only being a 1/4 thick I could scrap it off the metal.

My reason for seeing if it would come off was thinking if I ever had to replace the metal roof. So buy good metal as it will not come off.

A spin off I noticed right away was that it stiffened the building's roof structure. My shops both have a full six inches in the ceiling. They both have four inch purlins. So the foam completely covers them. When it is windy now the trusses do not move any at all. Before they would move some. I mean HIGH winds 50-60 MPH.
 
[b:654c4848f0]Tyvek is a 'one way' membrane. Label up under a metal roof - no moisture penetration.[/b:654c4848f0]

So now I have a decision to make.
Believe you or the manufacture.
Direct copy and paste for the DuPont web site.

Is DuPont? Tyvek? a vapor barrier?

No, DuPont? Tyvek? is not a vapor barrier. It is made with unique material science to keep air and bulk water out while allowing moisture vapor inside walls to escape.


Can you install Tyvek? WB with the lettering facing inwards or upside down?

Tyvek? HomeWrap?, Tyvek? StuccoWrap?, Tyvek? DrainWrap? and Tyvek? CommercialWrap? are equally effective in both directions and the logo may be on the inside or outside. However, Tyvek? StuccoWrap? and Tyvek? DrainWrap? have a specially engineered surface that should be placed with the grooves facing outwards in a vertical direction.


So per the manufacture Tyvek will allow moisture vapor threw it in either direction.
 
(quoted from post at 14:00:38 10/06/19) I called around and many insultors recommend open cell foam on metal roof.

Then I ran across this article.

An open-cell foam (about 0.5-pound density) is the most cost-effective way to insulate, but any opening over 1/16" could cause the foam to expand out onto the roof. It would be better to use a closed-cell (2-pound density) foam because it doesn't expand as much as open-cell and is more likely to fill voids but not go through them. In our neck of the woods, closed-cell foam costs about 56% more than open-cell.

Closed-cell achieves about twice the R-value per inch (open being 3.5 and closed being 6-7), but the density is 4 times higher and therefore you are using a lot more material to cover the same area. Closed-cell foam also contributes additional rigidity to the roof (while remembering our minimum safety assumption). Closed-cell foam is a vapor retarder, while open-cell is more vapor-permeable. This is important because you do not want water vapor within the foam condensing at the juncture where it contacts the metal.

I want a vapor barrier, so I'm leaning towards closed cell.
 
Why are you guys insulating the bottom of the roof, you're not working in the attic ! Metal roofs usually sweat because of no vapor barrier on the floor, such as a concrete floor. Insulate the ceiling joist/bottom cord of the trusses, & then a ceiling covering, such as the same metal roofing, up & done, no painting required & more fire proof !
 
How flammable are other moisture barriers?
My contractor wanted to use fan fold.
Others want to use bubble wrap.
What moisture barrier is fire proof?
 
'To keep air and bulk water out, while allowing moisture inside walls to escape'. I am not questioning your research, BUT, it still sounds like a one way membrane to me. Heck, they make rain-suits out of the stuff. Cheers.
 
I had 2" of closed cell foam put in my shed ceiling and walls. It turned a building that snow would drift inside into an igloo cooler. The plans were for just heating it in the winter, but being closed up caused enough humidity build up that I got a layer of mold on everything the first summer. I ended up with a mini split system that does both heat and cooling. When it gets down to around zero it needs help to keep up. I have a small pellet stove that picks up the slack well.
 
I don't know what all this condensation is. We have a few sheds with Steel roofs even been there for decades. You guys act like it is raining through the steel. Ours are not heated nor fully enclosed except one and it does not drip. We used to keep feed additives in there and none got wet. Salt soybean meal things such as that. Yes the feed grinder and metal equipment might get condensation on then but then so do all the other things when the air has the right temperature and dampness in it. When the temperature is right you can see the frost line on the tires for the chloride level on them.
 
(quoted from post at 08:13:22 10/06/19) Times are changing.
Roofer doesn't like the idea of putting osb and shingles on a 14ft building.
Condensation hasn't changed.
BIL has foam on his 14 foot metal roof.
So this old dog may have found a solution to condensation.

Are you talking about a new structure, or a new roof? I just replaced my house roof, I left the shingles intact, only one layer, and put new decking on, then metal. Looks great, will last my lifetime. On a barn, the roof was in good shape, but needing a new one in a few years. Trying to get ahead, I left the shingles on, cut off the drip edge flush with the roof boards. Then synthetic underlayment, stapled to the roof. Much better than the old tar paper, and lighter. . It is a vapor barrier, and is textured, so it isn t as slippery as tar paper. As long as the roof is reasonably flat, you don t need to strap the roof. I expect it will outlast me by a good bit, and I m 64.
 

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