This paper deals with the evaluation of thermal insulation performance of metal framed lightweight walls. This technology, more and more popular also in Italy, offers interesting advantages, but available commercial documentation lacks in reliable information about the real thermal insulation performance of the whole building envelope taking into account all the details and related thermal bridges. In other countries the available knowledge has been completed after long time and the recent growth of insulation performances requires something more than a simple Italian translation. In this paper the main envelope solutions are identified. The thermal transmittance has been calculated using a specialized freeware FEM application (THERM [1]) and the results checked with a commercial HAM application (WUFI [2]). The existing simplified methods have been extended in order to take into account also the most recent solutions proposed and realized, for a simple assessment of the real (corrected) avera ge thermal transmittance, far from singular points. Finally the main thermal bridges have been analyzed, optimized and used to calculate the average thermal transmittance of a standard façade module comparing it with the non-corrected U-value.