This International Standard sets out ways of expressing the energy performance in an energy performance certificate of a building (including the technical building systems) and ways of expressing energy performance requirements. This includes an overall numerical energy performance indicator and classes against benchmarks. This International Standard additionally includes numerical indicators at system or component level. This International Standard defines the different types of rating (such as calculated, measured, design, and tailored rating) and the energy uses to take into account (such as heating, cooling, domestic hot water, ventilation, and lighting). This International Standard defines a) overall indicators to express the energy performance of whole buildings, including heating, ventilation, air conditioning, domestic hot water, and lighting systems (this includes different possible indicators), b) ways to express energy requirements for the design of new buildings or renovation of existing buildings, c) procedures to define reference values, and d) ways to design a procedure for building energy certification. Furthermore, it provides a (calculation) link between delivered energy and the energy performance indicators for buildings. Since a building generally uses more than one fuel (e.g. gas and electricity), the different energy sources are collected per energyware. The overall rating is based on a weighted sum of delivered energywares. The weightings can be related to, for instance, primary energy or CO2 emissions to provide the end result of the calculation of energy performance. It also provides calculation procedures to assess the energy performance on the basis of measured energy use, including ways to convert the measured values to values under standardized conditions (environment, user). Finally, it defines the system boundaries needed to make a distinction between building energy needs, technical building systems, energy supply systems on site, and distant energy supply systems. This International Standard can be applied to a group of buildings if they are on the same lot, if they are serviced by the same technical systems, and if no more than one of them has a conditioned area of more than 1 000 m2. This International Standard provides different options at different levels. When this International Standard is used to set up national or regional methods for expressing energy performance and/or for energy certification of buildings, the choices between the options shall not be made by the individual user but by authorized national or regional bodies.