NRCA has conducted limited R-value testing of polystyrene insulation products used as roof system components. The polystyrene insulation was tested to determine whether the tested values meet ASTM International's recognized values.
According to the U.S. product standard for polystyrene insulation, ASTM C578, "Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation," 15 types of polystyrene insulation are manufactured in the U.S. ASTM C578, Type VIII, designates 1.25 pounds per cubic foot nominal density expanded polystyrene (EPS) insulation typically used in roof system installation. ASTM C578, Type IV, designates 25 pounds per square inch compressive strength extruded polystyrene (XPS) insulation typically used in below-membrane roofing applications.
NRCA obtained multiple samples of new (uninstalled) 2-inch-thick EPS and XPS insulation from various manufacturers. The samples were provided to R&D Services Inc., Cookville, Tenn., for R-value testing conducted according to ASTM C518, "Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus." The samples' R-values were tested without additional aging. The samples ranged from three to eight months old.