The innovative aspect in Pro-GET-OnE (Proactive synergy for Greater Efficiency On buildings’ Envelopes) consists in the following holistic vision: To combine in a same integrated system based on pre-assembled components the highest performances (iii) in terms of i) Energy requirements – by adding (or substituting the existing with) new prefab and plug and play high energy performing envelopes ii) Safety – by using appropriate steel structures to reduce horizontal loads and implementing the structural safety while supporting the new envelopes (timber for opaque parts/surfaces, glass, PV and solar panels) iii) Social sustainability – by ensuring tailored and customized solutions for users and increase the desirability of retrofit options. Building upon the previous experiences, Pro-GET-OnE aims at promoting a holistic optimized approach that goes beyond the results of EU and national projects and the IEA report on Prefabricated Systems for Low Energy Renovation of Residential Buildings. In fact, PRO-GET-ONE proposes the highest transformation of the existing building’s shell with volumetric increase and buffer zones (i.e. sunspace between the building and the outdoor environment, extra room, etc.). These solutions have been designed and analysed in a large set of existing buildings. Being the openings guaranteed, this solution would efficiently provide an effective zone to reduce thermal losses in the cold winter season while ensuring shadow during summer.