Open Cell Spray Foam On Metal Roof

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.

Open cell spray foam on metal roof.

It rots roofs people have told me. Your metal roof expands when it s hot and contracts when it s cold. 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. There are some cases where i could see some challenges.

Since spray foam is monolithic and closed cell it will create a watertight barrier over the entire metal roof. Spray polyurethane foam insulation with metal. That s an important consideration because if there s a leak in the roofing or the ridge cap moisture could get trapped between the roof and the insulation. 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.

Not long ago someone even told me that in florida roofing companies won t let their workers go up on roofs with open cell spray foam because the roofs are so spongy the guys fall right through. One would be if someone went on the cheap and used open cell spray foam rather than closed 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. 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.

About open cell spray foam kits. Murmurs and hearsay about open cell spray foam insulation have been gaining traction for a while. Closed cell spray foam insulation has a tendency to fill voids and gaps because it doesn t expand as much as open cell insulation. Closed cell foam provides better insulation than open cell and also functions as an air barrier.