Within the Greek framework for Energy Performance Certificates (EPCs) the methodology is based on a calculation tool with specifications according to the directives of the Technical Chamber of Greece and to the Energy Performance of Buildings Regulations (K.En.A.K.). The procedure refers to the “Energy Efficiency at Household Buildings” Programme. The energy auditor examines the building and issues the EPC for the existing condition and then proposes appropriate interventions in order to improve the energy efficiency. Once the interventions are completed, the energy auditor must examine again the building, certify that the proposed interventions were implemented and issue the new EPC. The values reported in the new EPC are the ones that are compared against the design values of the first EPC.