This standard defines the uses of energy to be taken into account for setting energy performance ratings for new and existing buildings, and provides: a) A method to compute the asset rating, a standard energy use that does not depend on occupant behaviour, actual weather and other actual (environment or input) conditions. For this, occupancy, climate and some other data that do not depend on the building itself are conventional ones, depending on the intended use of the building and on the climatic zone considered. b) A method to assess the operational rating, based on the delivered energy. c) A methodology to improve confidence in the building calculation model by comparison with actual energy consumption. d) A method to assess the energy effectiveness of possible improvements. It is up to national bodies to define under which conditions and for which types of buildings the various ratings apply.