The extended exergy analysis method, taking into account the mean life time cycle of building, has been applied to evaluate the sustainability of an urban area. The impact of the emissions due to the life cycle of the buildings has been evaluated. Two thermodynamic indexes, ηI and ηII showing, respectively, the first and second law efficiency of buildings, have been proposed as thermodynamic indexes. The applied methodology provides a single thermodynamics environmental criterion for the selection of technological alternatives, strategies and designs that produce lower environmental impacts connected to higher exergy indexes ηII.