This European Standard specifies a measurement procedure to determine the thermal transmittance of glazing with flat and parallel surfaces. For the purpose of this Standard, structured surfaces may be considered to be flat. This European Standard applies to multiple glazing with outer panes which are not transparent to far infrared radiation (in the wavelength range 5µm to 50µm), which is the case for soda lime silicate glass products, borosilicate glass and glass ceramics. Internal elements can be far infrared transparent. The procedure specified in this European Standard determines the U value (thermal transmittance) in the central area of glazing. The edge effects due to the thermal bridge through the spacer of an insulating glass unit or through the window frame are not included. Energy transfer due to solar radiation is also excluded. The procedure specified in this European Standard should be considered only when the thermal transmittance of the glazing cannot be calculated in accordance with EN 673. The determination of the thermal transmittance is performed for conditions which correspond to the average situation for glazing in practice. NOTE Patterned glass is an example of a glass with a structured surface;