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.
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.