In Budapest, one third of the population lives in large prefabricated housing estates. Therefore, this Modern heritage of the Communist period is one of the key issues of sustainable urban development. The majority of scientific studies on mass housing focus on economic and social aspects, so this research intends to approach the subject from the built-up environment. Taking the people’s needs and Budapest’s specific situation in relation to the challenges of sustainability as a starting point, the paper attempts to use the back-casting method based on social, economic and environmental trends. Defining a theoretically desirable future for this dominant type of urban housing, the analysis works backwards to understand their principal historic turning points. What are the values of large prefabricated housing estates? What were they, and what could they be? How can this modern and open urban form be sustained? What elements of the existing built environment will disappear, and what can be adapted in the transition process? By introducing three different scales — city, neighborhood and building, along with their subcategories – it is possible to recognize the effects of changing socio-economic conditions upon the built context and indicate problem-oriented, locally-minded interventions.