Most steel roofing is factory finish painted which adds yet another barrier surface in the interior primer paint coat which further isolates the steel from the spray foam.
Open cell spray foam on metal roof.
In warm climates zones 1 through 4 low density open cell spray foam insulation is the typical choice since it is vapor permeable and will allow drying of the exterior sheathing and roof framing if they happen to get wet via diffusion into the interior of the building.
There are some cases where i could see some challenges.
Versi foam open cell foam kits have a density of approximately 0 75 pounds per cubic foot.
Your metal roof expands when it s hot and contracts when it s cold.
Closed cell foam provides better insulation than open cell and also functions as an air barrier.
Closed cell spray foam insulation has a tendency to fill voids and gaps because it doesn t expand as much as open cell insulation.
If you use open cell spray foam on your roof rafters you should cover the finished application with a paint or sealant that retards water vapor.
Since spray foam is monolithic and closed cell it will create a watertight barrier over the entire metal roof.
It is 92 open cell and has an insulation r value of 4 lower than the other versi foam systems but still superior to some of the other commonly used insulation materials.
Murmurs and hearsay about open cell spray foam insulation have been gaining traction for a while.
One would be if someone went on the cheap and used open cell spray foam rather than closed cell.
It rots roofs people have told me.
Other considerations to get the best performance out of spray foam insulation you must cover the roof rafters and surrounding areas as thoroughly as possible.
Closed cell foam differs from open cell in that it prevents water entry minimizes moisture vapor permeability and decreases air leakage making it the preferred insulation to apply to metal panels.
Spray polyurethane foam insulation with metal.
About open cell spray foam kits.