Climate neutrality by 2050 is a priority objective and reducing greenhouse gas (GHG) emissions, increasing energy efficiency, and improving the circularity processes of resources are the imperatives of regulatory and economic instruments. Starting from the central themes of the mitigation of the causes of climate change and the interdependence represented by the water–energy nexus, this research focuses, through the application of the principles of the circular and green economy, on deep energy zero-emission renovation through the improvement of circularity processes of water resources in their integration with energetic ones on the optimization of their management within urban districts, to measure their capacity to contribute towards reducing energy consumption and CO₂ emissions during water use and distribution in buildings. After defining the key strategies and the replicable intervention solutions for the circularity of water resources, the investigation focuses on the definition of the research and calculation method set up to define, in parallel, the water consumption of an urban district and the energy consumption necessary to satisfy water requirements and CO₂ emissions. Starting from the application of the calculation method in an existing urban district in Rome, 10 indicators of quantities have been developed to define water and energy consumption and their related CO₂ emissions, focusing on the obtained results to also define some interventions to reduce water and energy consumption and CO₂ emissions in territories that suffer a medium-risk impact from contemporary climatic conditions.

The European Commission strategic long-term vision for a prosperous, modern, competitive and climate-neutral economy by 2050 outlines main strategic blocks to maximise the benefits of energy efficiency, including zero emission buildings and to maximise the deployment of renewables and the use of electricity to fully decarbonise Europe’s energy supply. The following EU Climate Target Plan 2030 underlines, once again and even more urgently than in 2050, the strong need to build a modern, sustainable and resilient Europe, and this high objective means cleaner air, more energy security and more energy-efficient buildings. Looking at these European directives, Italy has signed the PNIEC, with whom intends to pursue an indicative target of reducing consumption by 2030 equal to 43% of primary energy and 39.7% of final energy compared to the PRIMES 2007 reference scenario. To achieve this goal, particular attention is paid to the existing buildings such as Palazzo De Simone. This historical building, built in the eighteenth century on a project by the architect Raguzzini, located in Benevento (BN), is now home to four different uses: the De Simone Theatre, the De Simone Chapel, a faculty of the University of Sannio and the Conservatory of Benevento. Starting from an extensive historical research, as well as from a series of non-destructive in-situ surveys and environmental measurements, it has been possible to create a satisfactory analysis framework. Later, the design objectives have been identified and, starting from these, design strategies and solutions have been formulated. It has been decided to act at a global level with a conservative restoration in compliance with the constraints imposed by the Superintendence, and at a specific level first on the building envelope, leaving the systems unchanged, then on the systems, leaving the envelope unchanged. Finally, crossing the results, the transformation of the historical building in a nZEB has been obtained, in compliance with the legislative constraints imposed by the national regulations.

The next decade will see severe environmental and technological risks, pushing our adaptive capacity to its limits. The EPBD Case Green directive, to counter this phenomenon, emphasizes accelerating building renovations, reducing GHG emissions and energy consumption, and promoting renewable energy installations. Additionally, it calls for deadlines to phase out fossil fuels and mandates solar system installations. This research provides a comprehensive perspective on the opportunities for and challenges of incorporating renewable energy into the built environment. It focuses on the 2961 residential buildings on Procida, a small island located south of Italy, to efficiently utilize energy resources and lay the groundwork for sustainability. Beginning with an analysis of the territorial, urban, historical–conservation, structural, and geological context, in addition to environmental assessments, the research develops a classification and archetypalization system using in-house software. This system aggregates data on the island’s residential buildings, analyzes their current state, and formulates various intervention scenarios. These scenarios demonstrate how integrating technological–environmental design interventions, such as upgrading the building envelope and enhancing bioclimatic behavior, with energy retrofitting measures, such as replacing mechanical systems and installing solar panels, can improve the overall performance of the existing building stock and achieve energy self-sufficiency.

The transition away from fossil fuels towards a carbon-neutral, clean and circular economy is one of the greatest challenges of our time. Energy communities are one of the tools to re-structure our energy systems by harnessing the energy and allowing citizens to participate actively in the energy transition and thereby enjoy greater benefits. The definition of Renewable Energy Communities (RECs) given by the European Commission, places the REC as an association that produces and shares renewable energy, generating and managing cost-effective green energy autonomously, reducing CO₂ emissions and energy waste. Observing this definition, the new Italian regulations concerning RECs boost distributed generation, encouraging the development of ‘zero-mile’ local energy production and smart grids. This research aims to evaluate the conditions to propose a REC in the Tor Sapienza district, as an Italian prototype, assessing the possibilities and advantages of transforming it into a large-scale sustainable infrastructure by means of a deep energy transition and the active role of local citizens, public administrations and small and medium-sized enterprises. Thanks to an in-depth technological, environmental and demographic survey of the neighbourhood, the study focuses on the retrofitting of a social housing complex in Tor Sapienza, as the main prosumer of the REC.