In relation to Royal Decree 235/2013, of April 5, which approves the basic procedure for the certification of energy efficiency of buildings.

The energy efficiency certificate or energy certificate is an official document written by a competent technician that includes objective information about the energy characteristics of a building. In this sense, energy certification qualifies a building energy by calculating the annual energy consumption needed to meet the energy demand of a building under normal conditions of occupation and operation. (Including hot water production, heating, lighting, refrigeration and ventilation). The energy certification process concludes with the issuance of an energy efficiency certificate and the assignment of an energy label. The energy rating scale is seven letters and varies between the letters A (most energy efficient building) and G (least energy efficient building). The energy label expresses the energy rating of a building by giving one of these letters. This certificate is mandatory, with exceptions, for the owner of any individual part of an existing building (dwellings, offices or premises) subject to a sale or rental transaction.
As of June 1, 2013, it is mandatory for the owners of the buildings or part of them to include in any offer, promotion and publicity directed to the sale or rental of the same, a badge called “Efficiency Label Energy “that identifies the level of energy efficiency rating obtained by the building.

This “Energy Efficiency Label” will be obtained once the energy efficiency certificate issued by a competent technician has been obtained and will have to be registered. The owner must register it in the register of certificates of energy efficiency created for this purpose by the Autonomous Communities and that will have a validity of 10 years.
From the normative point of view, the current rule requires that all existing buildings, when sold or leased, have an energy efficiency certificate. Therefore, it is mandatory to have such certificate (the notary will ask you) before proceeding to make the sale. At the time of signing the contract for the sale of the property, the energy efficiency certificate obtained must be made available to the acquirer. When the contract is a lease, it will suffice merely to display and make available to the lessee a copy of the said certificate.
Failure to comply with the precepts contained in the aforementioned rule shall in any case be considered a violation of the certification of energy efficiency of buildings and shall be sanctioned in accordance with the provisions of the legal range applicable, such sanctions vary between The 300 and 6,000 euros. In addition, such breaches may constitute breaches in the defense of consumers and users.