Urban decay and obsolescence of post-war mass housing is a global phenomenon. Although the reasons for housing deterioration are different, the altered relationship between public and private spaces is essential for the mass housing. The research hypothesizes that strong polarisation of the urban landscape into private and public is firmly influencing urban decay and obsolescence of post-war mass housing neighbourhoods. Taking New Belgrade blocks as the case study, the research investigates this correlation, following the gradual transformation of the urban landscape of modernity in parallel with different factors. Moreover, the research sheds light on the specific Yugoslav housing policy and developed collective self-management of the urban commons from the time of construction. Although these strategies have been neglected over the time, they are valuable for contemporary, increasing discussions on community-driven approaches for comprehending and managing change in urban environment, specifically for residential neighbourhoods. Furthermore, the research is analysing different contemporary strategies and community practices that are reinventing the public-private relationship in the context of mass housing, contributing to the development of a methodology for mitigating obsolescence and causes of housing deterioration. The methodology is revitalizing the important value of common spaces and the role of community and is reusing the modernist idea of co-creation, contributing to inheritance of the modernist concepts. Moreover, if applied, it would increase liveability of urban space and well-being of its residents, contributing to transformation strategies for adaptation to current needs, and therefore ensuring vitality of mass housing as a core typology of the Modern Movement.