This type of ceiling system is only intended for use on horizontal timber roof joist elements and not for sloping roofs. The testing and certification we have for these systems, rated at 30, 60 and 120 minutes integrity and insulation, does not include installation at an angle and doesn't readily lend itself to the dimensions normally associated with this part of a timber roof construction, as each of these systems requires deep layers of stone wool insulation above the line of the Supalux® boards.