This project transforms the vacant Terzo Palazzo, a former office headquarters in San Donato Milanese, into a cooperative housing community addressing housing, social and environmental challenges. The proposal reuses the existing structure, reducing material consumption, construction waste and embodied carbon while extending the life of a 35,000 m² office complex. The project demonstrates how obsolete office buildings can become resources in responding to the housing crisis. The intervention promotes an intergenerational community bringing together students, young adults, elderly residents, immigrants and care-dependent individuals. Housing is organised through flexible clusters combining private units with shared kitchens, living rooms and collective facilities, encouraging cooperation and efficient resource use. At the urban scale, the project reconnects the building with the city through community spaces and mobility infrastructures, transforming an isolated corporate complex into an active civic hub. Adaptability is a central design principle. Housing units are conceived as flexible frameworks capable of evolving with changing needs and family structures, ensuring long-term affordability. By combining adaptive reuse, social inclusion and environmental responsibility, the project proposes a model for regenerating underused buildings. The Terzo Palazzo becomes a living infrastructure supporting collective wellbeing and a more sustainable future.