The big picture concern is actually more about trapped moisture than whether the substances that make up spray foam insulation will corrode steel or metal sheets.
Open cell spray foam metal roof.
Spf insulation consists of isocyanate and polyol resin that is chemically combined and applied to surfaces using a spray gun.
In our neck of the woods closed cell foam costs about 56 more than open cell.
Less common of the two types of spray foam open cell is mostly used for residential and commercial insulation.
Closed cell foam provides better insulation than open cell and also functions as an air barrier.
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 or closed cell spray foam is applied to the underside of the roof sheathing and additional fiberglass or cellulose insulation is blown in as a cost saving method for meeting high insulation requirements and filling in the cavity space between the rafters to the ceiling deck.
Open cell spray foam can also be used to create an unvented attic in cold climate zones provided code requirements for a vapor retarder are followed.
One would be if someone went on the cheap and used open cell spray foam rather than closed cell.
However i own a spray foam rig and i wouldn t bother putting more than about 8 of open cell or 5 closed cell.
Moisture from indoors can diffuse through the foam and find the cold roof sheathing where it accumulates and eventually rots the roof.
How ducts in an unvented attic should be installed.
We already know open cell spray foam is risky in cold climates.
I prefer spraying open cell over the rafters when possible because it avoids shrinkage problems that can occur with such foams.
As a result in iecc climate zones 5 and higher building codes require the use of a vapor retarder if you install open cell spray foam.
Some spray foam manufactures have tested primer coating products that result in the formulation of a class ii vapor retarder directly on the surface of the open cell spray foam.
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.
There are some cases where i could see some challenges.
Open cell spray foam is made of open cells that are softer and flexible with the physical structure similar to a sponge shape.
Strong material that can strengthen walls roofs structure.
Open cell spray foam.
Open cell foam provides insulation and air sealing for a building but is water and vapor permeable.