FTT highly-energy efficient roof windows have been designed taking into account the stringent requirements of passive construction. This specialized and innovative design provides excellent performance by ensuring high efficiency of thermal energy. FTT U8 Thermo with the U value of 0.58W/m2K is the most energy-efficient roof window on the market. The window is supplied and installed in conjunction with EHV-AT Thermo flashing. The window glazing unit is set in a specially designed sash frame, utilising thicker timber profiles, thus reducing the risk of thermal bridging and improving overall thermal performance of the structure. FTT window can be equipped with highly energy-efficient glazing units: - double-chamber U6 glazing unit offering U value of Ug=0.5 W/m2K as standard. The overall heat transfer coefficient for the whole FTT U6 window is Uw=0.81W/m2K. The internal glass is laminated (safety glass) and fulfils the requirements of class P2A. - Optionally, the window can be fitted with a triple-chamber U8 glazing unit with Ug=0.3W/m2K.