Vienna is the fastest growing metropolis in Europe: In 2017 alone, the city grew by 21.194 people and in the last ten years by 217.555. The development forecasts of MA 23 and Statistics Austria do not foresee a significant change in the coming years. New city expansion areas, such as the Seestadt-Aspern, are set up in no time and new parts of the city are being built in former rail station areas (such as the North and Central rail stations). But this newly created housing is still not enough, and the sealing of land should be sparingly handled. Indeed, it should be the last option. In addition to the expansion of the attic in old buildings, there are other ways of in-creasing the density within the existing area. One could be the constructional supp-lement structural addition of retail stores. At the centre of this thesis is an example of design for a building on the rooftop of a supermarket and its parking space, thus creating additional space for apartments and offices. The flats are designed as small apartments (for one to two people) u-sing space-saving furniture easily stowable when not in use. For example, in additi-on to the basic equipment, a room in a shared apartment with only 18.2 m has a fold-out guest bed, so the living space can be used flexibly. The planned project was evaluated according to the criteria of Klimaaktiv (quality level Gold).