The housing crisis today is not only quantitative but also qualitative. Households have become increasingly diverse and dynamic: single-parent families, blended families, boomerang children, home-workers, non-family cohabitations…, yet housing production remains standardised and rigid. To address this paradox, we developed the Design Principles for Socially Adaptable Housing: a research-based and transferable framework: 1-Research into household diversity and evolving spatial needs; 2-Translation of these needs into spatial solutions; 3-Distillation into an applicable set of 10 Adaptability and 8 Quality Principles; 4-Development of new housing typologies and floor plans; 5-Built case study: START-Ivry. Here, housing adapts to people, not the reverse. Super-adaptable and divisible dwellings, equipped alcoves, movable kitchens, carefully designed layouts… allow homes to meet present needs and evolve as lives change. Adaptability becomes a form of circularity at the scale of the dwelling: the most sustainable square metre is the one that does not need to be rebuilt. The Principles translate inhabitants’ needs into architecture. They provide a practical tool for municipalities, developers, and architects. They are also used in academic contexts, such as London Metropolitan University, and have informed policy documents in Paris, Ivry, and soon in Amsterdam. Socially adaptable housing is no longer a distant ideal, but a practical and scalable form of social infrastructure.