This European Standard specifies a method for calculating the thermal transmittance of curtain walls consisting of glazed and/or opaque panels fitted in, or connected to, frames. The calculation includes: - different types of glazing, e.g. glass or plastic; single or multiple glazing; with or without low emissivity coating; with cavities filled with air or other gases; - frames (of any material) with or without thermal breaks; - different types of opaque panels clad with metal, glass, ceramics or any other material. Thermal bridge effects at the rebate or connection between the glazed area, the frame area and the panel area are included in the calculation. The calculation does not include: - effects of solar radiation; - heat transfer caused by air leakage; - calculation of condensation; - effect of shutters; - additional heat transfer at the corners and edges of the curtain walling; - connections to the main building structure nor through fixing lugs; - curtain wall systems with integrated heating.