The Spray Polyurethane Foam Alliance (SPFA, www.sprayfoam.org) and National Roofing Contractors Association (NRCA, ) are two industry trade associations that offer a great deal of information on SPF roofing. Both organizations agree that when used as roofing foam, the physical properties of SPF suggest the use of spray foam with a minimum compressive strength of 40 pounds per square inch or higher. This is a general guideline that will work in all parts of the United States. Less compressive strength foams are used where less foot traffic is anticipated or where the geographic area is not as hard on construction materials.
You can’t walk on SPF roofs.