The Netherlands faces a significant housing shortage alongside a steady rise in single-person households, a combination that increases the risk of social isolation in daily life. This graduation project investigates how the design of shared transition zones in a mixed-use residential building can support informal social inclusion without relying on programmed activities or community management. Drawing on the theoretical work of Jan Gehl, William H. Whyte, and Richard Sennett, three spatial conditions are identified as central to everyday encounter: intimacy, visibility, and programmatic activation. These conditions are translated into three architectural principles, light, gradient, and threshold, that shape the design of a mixed-use apartment building located in the Spaanse Polder in Rotterdam. The building's stepped form ensures direct sunlight reaches a central courtyard, the spatial organisation creates a gradual transition from public to private rather than a hard boundary, and semi-private threshold zones at each dwelling entrance allow residents to be present in shared space without being exposed. Through case study analysis, research by design, and physical modelling, the project demonstrates that social inclusion in housing is less a matter of organised programming than of careful spatial design, where the gallery, courtyard, and threshold are treated as primary architectural spaces rather than residual circulation. The project concludes that meaningful collective life depends on the coexistence of encounter and retreat, and that the most socially valuable spaces in a building are often the ordinary ones that ask nothing of the people who pass through them.