Approval of the European Directive 2002/91/EU was followed by its reformulation in Directive 2010/31/EU, with reference to the Energy Performance of Buildings (EPBD). The partial transposition of this norm in Spain took place through Royal Decree 235/2013, which describes the Basic Procedure for the Energy Performance Certification of Buildings and acknowledges four different documents to certify the energy simulation of buildings: (i) CALENER VYP as the general method, and (ii) CE3, CEX and CERMA, as simplified methods. This study analyzes and compares these documents through the qualified opinions of a panel of 105 multidisciplinary professionals of the sector that determined the strengths and weaknesses. To this end a survey was drawn up, including aspects as diverse as: the background and professional characteristics of the experts, the types of residences studied, the characteristics of the documents, the means of processing documents, and the final results in terms of reports and energy certifications. Data analysis shows that most technicians prefer using programs with a simple interface-namely, the CEX. Although all the documents recognized are equally valid for energy certification, when certain types of residence are involved, there may be as much as a 26% difference in the determination of CO2 emissions. This translates into a higher or lower level in the final energy certification obtained for a building. (C) 2015 Elsevier B.V. All rights reserved.