The document specifies methods for the calculation of the thermal transmittance of windows and doors consisting of glazed or opaque panels fitted in a frame with and without shutters. It allows for different types of glazing (glass or plastics; single or multiple glazing; with or without low emissivity coatings, with spaces filled with air or other gases), various types of frames (wood, plastic, metallic with and without thermal barrier; metallic with pinpoint metallic connections or any combination of materials), the additional thermal resistance introduced by different types of shutters, depending on their air permeability. The document does not apply to curtain walls and other structural glazings which are not fitted in a frame, as well as to roof windows.