In the context of European efforts to reduce energy consumption and CO2 emissions in the building sector, the second recast of the Energy Performance of Buildings Directive promotes the acceleration of the energy renovation of European building stock. To do this, a cost optimization is necessary to find the best combination of energy efficiency measures which minimize the global cost during the entire life-cycle of the building, as suggested in the first recast of the same Directive. Since a great number of combinations must be analyzed, an automated procedure is necessary to reduce the calculation time. In this work, an iterative input-output process is set, thanks to the coupling of a dynamic energy simulation software (TRNSYS) and a generic optimization software (GenOpt). The cost optimization is applied to a new social housing construction - a multi-family building located in Northern Italy. The methodology that was adopted allows the simultaneous optimization of both the building energy demand (building envelope) and the building energy supply (technical systems and renewable sources). Results are compared with those obtained using a more widespread sequential approach whose purpose is firstly the optimization of one of these two factors, and subsequently the optimization of the other one. This study has demonstrated that an integrated approach allows a larger number of possible combinations of energy efficiency measures to be explored with respect to the sequential approach.