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[Display omitted] • The transition of building districts to sustainable energy communities is addressed. • The case study is set in a real social housing district in Naples, South Italy. • Brute-force optimization is used to drive the transition maximizing sustainability. • Design variables include envelopes, energy systems, renewables, storage, control. • A multi-objective approach is applied to trade-off sustainability and costs. The decarbonization of the energy industry is essential to achieve a future net-zero energy system. To maximize the capacity of citizens to contribute to the clean energy transition, sustainable energy technologies are mandatory. Accordingly, the development of nearly-zero energy districts and communities is up-to-date, and, about it, the net-zero energy goal requires a challenging combination of building design and retrofit, renewable energy sources, energy storage systems. This manuscript investigates several alternative solutions for a shared energy system, to turn a 29-building social housing district in Naples, Southern Italy, in a nearly zero-energy community. The method is quite articulated, based on various numerical approaches, applied by the cycling use of many programs, namely: DesignBuilder® for the building modeling, EnergyPlus as simulation tool, and MATLAB® as optimization engine. A sustainability index based on emissions is introduced. A first optimization is carried out to maximize the sustainability index of the energy community, with a brute-force algorithm used to investigate several design variables, that address building envelopes, energy systems, renewables, electric storage, and operation strategies, resulting in 2,224,044 solutions explored. A second multi-objective optimization is then performed on a limited number of solutions, to evaluate not only the energy-environmental aspects but also the economic ones. The analyzed solutions have a minimum sustainability level equal to 85% and it shows a suitable combination of common buildings retrofit measures. Finally,in order to be able to achieve generalizable results, possible energy and economic targets are outlined: sustainability levels of 85%, 90%, and 95% with an investment budget of up to 150–200 €/m2. [ABSTRACT FROM AUTHOR]