Spray polyurethane foam- (SPF-) based roof systems are constructed by mixing and spraying a two-component liquid that forms the base of an adhered roof system. The mixture expands 20 times to 30 times its liquid volume and forms a closed-cell foam insulation. An elastomeric coating usually is applied to the foam insulation and provides the long-term weatherproofing characteristics of SPF-based roof systems.
Polyurethane foam flashings with elastomeric coatings, as depicted in the detail, are sprayed in place and become an integral component of an SPF-based roof system. SPF forms a monolithic, continuous, self-adhered flashing detail. At skylight penetrations, SPF is applied to form a fillet or cant at the base of a skylight curb and then is applied up the vertical surface to a desired flashing height. A polyurethane foam flashing detail requires an elastomeric coating up the curb and above the termination line of the SPF.
At skylight curbs, the SPF should terminate a minimum of 6 inches (152 mm) above the horizontal SPF roof surface with the elastomeric coating extended a minimum of 2 inches (51 mm) above the SPF.