La Borda is a self-organised housing cooperative in Barcelona that proves affordability, community and climate responsibility can reinforce each other. One of its most powerful sustainability moves happens before materials or systems are even chosen: the programme is rationalised. By shifting “extra” square metres from private flats into shared spaces, the cooperative reduces built area and duplicated appliances while increasing usefulness—kitchen–dining room, laundry, multi-purpose room, guest room, health & care space, storage, patio and roof terraces extend daily life beyond the home. Fewer metres to build and condition means less embodied carbon, lower resource use and lower bills, without sacrificing comfort or quality of life. Environmental performance then builds on this demand-first logic. A low-carbon timber primary structure replaces conventional high-impact materials and supports a dry, efficient construction process. The envelope is optimised for thermal performance, and the central courtyard typology brings daylight deep into the plan while enabling cross-ventilation and shaded semi-outdoor transitions that temper summer conditions. With passive measures prioritised over technology, space-heating needs are effectively eliminated in normal operation and operational energy is kept exceptionally low. Programmatic choices reinforce the same strategy: the project renounces an underground car park, avoiding the carbon and excavation of basements and reallocating budget to performance and shared amenities. Together, these decisions stabilise long-term living costs and help remove the risk of energy poverty for residents within a 75-year public land lease. Co-designed through resident workshops, La Borda integrates energy, materials, water and circularity criteria from early stages, turning measurable targets into everyday collective management.