This standard gives calculation methods for assessment of the annual energy use for space heating and cooling of a residential or a non-residential building, or a part of it, which will be referred to as "the building". This method includes the calculation of: a) the heat transfer by transmission and ventilation of the building zone when heated or cooled to constant internal temperature; b) the contribution of internal and solar heat gains to the building heat balance; c) the annual energy needs for heating and cooling of the building, using input from the relevant system standards referred to in this International Standard and specified in Annex A. The standard also gives an alternative simple hourly method, using hourly user schedules (such as temperature set points, ventilation modes, or operation schedule of movable solar shading). This method produces hourly results, but the results for individual hours are not validated and the results for individual hours can have large relative errors. Also procedures are given for the use of more detailed simulation methods to ensure compatibility and consistency between the different types of methods. The standard provides, for instance, common rules for the boundary conditions and physical input data irrespective of the chosen calculation approach.