This International Standard specifies detailed calculation procedures for determining the thermal and optical transmission properties (e.g., thermal transmittance, total solar energy transmittance) of window and door systems based on the most up-to-date algorithms and methods, and the relevant solar and thermal properties of all components. Products covered by this International Standard include windows and doors incorporating: a) single and multiple glazed fenestration products with or without solar reflective, low-emissivity coatings and suspended plastic films; b) glazing systems with pane spacing of any width containing gases or mixtures of gases; c) metallic or non-metallic spacers; d) frames of any material and design; e) fenestration products tilted at any angle; f) shading devices; g) projecting products.