The document specifies the measurement of thermal transmittance of frames and sash components of windows and doors including transoms and mullions. It is based on DIN EN ISO 8990. Measurements are performed under conditions which are representative of those found in practice. Edge effects occurring outside of the perimeter of the specimen are excluded. Furthermore energy transfer due to solar radiation is not taken into account, and air leakage is excluded. The test procedure is designed to take into account the whole development area of the frame or sash surface, but excludes the influence of the thermal bridge introduced througt the spacer in sealed glazing units. Thermal bridging effects of window or door furniture are included.