The work deals with the idea of an investment in an old apartment of a Wiener Zinshaus. Therefore, rental law regulations and investment figures are explained. Based on this knowledge, some apartments of a specific Zinshaus are examined for potential investment. There is a possibility to increase the yield and it results from an improvement of the flat category. An improvement requires the rearrangement of the floor plan. For this purpose, some examples of a renovation have been prepared and additional structural conditions are described. Whether the investment is profitable or not, can be calculated in a specially developed calculator.