Open Cell Spray Foam Metal Roof

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.

Open cell spray foam metal roof.

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. However i own a spray foam rig and i wouldn t bother putting more than about 8 of open cell or 5 closed cell. Open cell spray foam is made of open cells that are softer and flexible with the physical structure similar to a sponge shape.

I prefer spraying open cell over the rafters when possible because it avoids shrinkage problems that can occur with such foams. We already know open cell spray foam is risky in cold climates. How ducts in an unvented attic should be installed. One would be if someone went on the cheap and used open cell spray foam rather than closed cell.

In our neck of the woods closed cell foam costs about 56 more than open cell. 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. There seem to be no chemicals in spray foam that could react with steel or the galvanized protective coverings on the metal siding and roofing panels. Strong material that can strengthen walls roofs structure.

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. Moisture from indoors can diffuse through the foam and find the cold roof sheathing where it accumulates and eventually rots the roof. Spf insulation can be open cell or closed cell. Open cell foam provides insulation and air sealing for a building but is water and vapor permeable.

Closed cell foam provides better insulation than open cell and also functions as an air barrier. 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. There are some cases where i could see some challenges. 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.

Less common of the two types of spray foam open cell is mostly used for residential and commercial insulation.