Possible Foam Insulation Problem?

Question

Will spaying foam insulation to the underside of a roof deck cause problems with the adhesives in plywood and OSB? Being that this could cause the plywood to stay near 200 degrees during a summer day i'm beginning to wonder if it's possible that the plywood would become un-glued or delaminate.

Answer 1

Good question. The simple answer is no.

Adding foam to the underside of the roof will cause the shingle temperature to rise since you are adding more mass to store heat in the roof. The temperatures will still be no where close to causing delamination issues in the chip board or plywood.

However, most shingle warranties will void after you reach the 190 degree point on the roof. Plus, the foam will not let moisture through, so if the roof ever develops a leak, it will degrade and rot the wood substrate before you realize the problem.

I am not a big fan of installing the foam on the underside of the roof for the above reasons. It does work good, but has some potentially bad side effects.