Vienna is growing and with the city, the demand for residential space. Till today rooftop extensions as a tool for innercity development focused on buildings which where built around 1900,the so called "Gründerzeit". The thesis shows the potential of extensions of residential facilites, which where built just after the second world war until the late 1960s. In addition to the analysis of urban, architectural and structural features of buildings of this period, the European rules and standards, Viennese building regulations and information sheets are critically viewed at. The follwing chapters cover the features of timber constructions, which must be considered not only for its ideal ratio of weight and loadcarrying capacity within the legal restrictions, but also because it meets all demands of a sustainable and modern building method and is therefore perfectly suited for rooftop extensions. The parallel thermal refurbishment of the existing building as well as the securing of a barrier-free accessibility, raises the structural quality and should lead to the influx of new tenants and a balance of age groups. The second part shows on the basis of a building in the 14th district of Vienna, the practical implementation of the concepts described.