Abstract This paper proposes an analysis methodology that can be applied by governments and local administrations to evaluate energy retrofit programs that involve entire building categories. Through a simulation based approach, that combines detailed energy modelling and algorithmic optimization, the analysis methodology is aimed to assess the magnitude of achievable energy savings for various retrofit levels along a cost-optimal path towards achieving net zero energy operation conditions. The proposed approach allows to identify the most cost-effective energy efficiency measures (EEMs) for building retrofits and their required investment costs. The retrofit potential benefits of the Italian office buildings stock is used as a case study to illustrate the application of the proposed analysis methodology. The results of the evaluation analysis for the Italian office building stock indicated a potential primary energy savings of 54% (i.e., 8000 GWh), when retrofitted through optimal combinations of EEMs and rooftop integrated photovoltaics. The optimal set of EEMs showed strong dependency on building typology and climate. In general, the cost-optimal combinations of EEMs and rooftop PV systems did not allow to reach net-zero energy operation conditions for any Italian office building type and climatic zone.