XO/SK (T&G) is an engineered tongue and grooved external roof insulation system with robust facings which meets the passive U-value of 0.15 W/m²K. XO/SK (T&G) is an engineered tongue and grooved external roof insulation system with robust facings which meets the passive U-value of 0.15W/m2K. Using XO/SK improves detailing, speeds up the installation process and provides a uniform plane to detail more effectively. Creating a warm roof reduces the normal amount of junctions prone to thermal bridging greatly improving the thermal performance of the roof.