Following the Second World War, rapid and economical housing production emerged as a key challenge for Is-tanbul’s growing population. In the 1950s, municipal efforts resulted in the construction of affordable housing in Koşuyolu and Selamsız, two neighboring districts. Built with similar aims and designs, these settlements shared common features in their plan layouts, building sizes, and massing characteristics. However, the transformation of these housing projects and their surrounding areas has followed divergent trajectories over time, shaped by distinct socio-economic dynamics. Changes in land use, demographics, and functional or commercial differentiations have altered spatial arrangements, settlement character, and building usage patterns in both districts, with Selamsız largely retaining its original character, while Koşuyolu has undergone significant transformations. This study examines these transformations, highlighting how economic and societal dynamics in both districts and their surroundings influence the preservation of 20th century modern housing heritage.