The European Community introduced the energy certificate of buildings to reduce the energy consumption in buildings and emanated some standards in order to publicize the energy buildings certificate procedure. Consequently, to calculate energy performance of buildings (EPB), many numerical codes have been developed, which take into account several parameters in static or dynamic conditions. In this article three different models for EPB software calculations have been analysed and compared, in order to quantify their gap with the real energy consumptions. The study has been conducted considering a single-family house in Italy, and focused the differences among numerical codes and real consumption in relation with flexible architectural solutions, that are widely utilised especially in rural areas in Mediterranean countries.