Open Cell Spray Foam Metal Roof

Closed cell foam provides better insulation than open cell and also functions as an air barrier.

Open cell spray foam metal roof.

Open cell spray foam is made of open cells that are softer and flexible with the physical structure similar to a sponge shape. Less common of the two types of spray foam open cell is mostly used for residential and commercial insulation. 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. Moisture from indoors can diffuse through the foam and find the cold roof sheathing where it accumulates and eventually rots the roof.

We already know open cell spray foam is risky in cold climates. 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. How ducts in an unvented attic should be installed. However i own a spray foam rig and i wouldn t bother putting more than about 8 of open cell or 5 closed cell.

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. Open cell spray foam. 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. 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.

One would be if someone went on the cheap and used open cell spray foam rather than closed cell. There are some cases where i could see some challenges. Spf insulation can be open cell or closed cell. Spf insulation consists of isocyanate and polyol resin that is chemically combined and applied to surfaces using a spray gun.

I prefer spraying open cell over the rafters when possible because it avoids shrinkage problems that can occur with such foams. 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. In our neck of the woods closed cell foam costs about 56 more than open cell. Open cell foam provides insulation and air sealing for a building but is water and vapor permeable.

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.