The Energy Saving Ordinance (EnEV) came into force in 2002. It replaced the Thermal insulation Ordinance (1995) and the Heating Systems Ordinance (1998). The Energy Saving Ordinance sets energy performance requirements for new buildings and for existing buildings in case of major renovation. In exceptional cases there are requirements to retrofit. For non-residential buildings, the calculation of the primary energy demand is based on the DIN V 18599. The Energy Saving Ordinance also regulates the issue and the display of energy performance certificates as well as their content. The certificates serve as an information about the energy performance of a building and they are supposed to give the possibility to compare buildings in terms of the energy performance (for further information see lines 1193 ff.).