Energy Communities are based on principles of renewables, efficiency, local ownership, to improve energy supply and demand. This study evaluates performance of communities, moving from single buildings to the comprehensive performance. The method combines several tools, including DesignBuilder® and EnergyPlus for simulation, MATLAB® as optimization engine. To determine best options, three retrofit scenarios are compared using three performance indicators: primary energy consumption (PEC), CO2 emission, and running cost (RC). Moreover, evaluation of the investment - with specific economic indicators for helping the citizen to be able to understand the profitability of each individual intervention and so to help him in the choice once an economic constraint - is set. The first retrofit scenario involves insulation of both opaque transparent envelopes, while the second is a retrofit of only systems, through replacement of existing ones and introduction of renewable sources and batteries. Results show how the third scenario - a retrofit trade-off between the first two - offers the greatest PEC, CO2 emission, and RC reduction of 71.35%, 73.42% and 60.52%, respectively. Even from a purely economic view, the third intervention represents a better investment when considering annual economic savings, as shown by increasing net present values.