Directive 2002/91/EC on the energy performance of buildings. Member States are obliged to ensure that when buildings are constructed, sold or rented out, an Energy Performance Certificate is made available to the owner or by the owner to the tenant or potential buyer. The certification shall also include advices and information on how to improve energy performance. It concerns such elements as building envelope, windows, heating, electrical and ventilation instillations, lighting, heat sources (incl. boilers, CHP units) cooling systems and others.