The purpose of this standard is to: collate results from other standards that specify calculation of energy consumption within a building; account for energy generated in the building, some of which may be exported for use elsewhere; present a summary on tabular form of the overall energy use of the building; specify calculation of primary energy consumption and carbon dioxide emission for the building as a whole; establish general principles for the calculation of primary energy factors and carbon dioxide emission factors. This standard will provide: a definition of system boundaries (e. g. building, installations, energy supply) and calculation periods; general definition of the overall energy use (i.e. determine which services are taken into account within the system boundaries); definition of energy terms (energy use, primary energy, etc.); definition of the data interfaces with other standards in order to report the overall energy use of buildings; general procedures for taking into consideration decentralised energy production based on renewable energy and CHP (combined heat and power production), e. g. to show how on-site energy generation offsets energy demand; identification of the energy streams across system boundaries; principles for assessing primary energy consumption and CO2 emission of buildings (i.e. principles for determining primary energy factors and carbon dioxide emission factors); general principles for taking into account the interactions between the different energy uses (e. g. calculation of recovered losses and gains). The objective of specifying the details of the energy performance calculation for a building is to: underline the particularity of a project (e. g. efforts made on bioclimatic design); show the strong and the weak points in the overall energy performance of the building and to highlight potential gains: distinguish between thermal uses and specific electrical uses; indicate the outputs required from related standards, in which calculation of energy consumption of services within a building are specified. This work will be coordinated with CEN/TC TC 89, TC 156, TC 169, and TC 247.