It is an significant task to qualify and rank residential buildings based on various priority aspects and to make optimum allocation of the material resources available for the renewal of the buildings.To this end a model based on fuzzy logic was prepared. To construct and to test this model many detailed technical-static expert reports were available all related to a stock of residential buildings in Budapest. Based on this report a database was created. With the help of this database a model was prepared, calculating a so-called status characteristic value between 0 and 1 on the basis of the structures and status of the buildings. For this calculation a fuzzy singleton signature model was prepared. Based on this a hierarchy can be set up related to the stock of buildings, which is suitable for supporting the decision making on intervention. The model was examined by using the created database. Membership values characterising the status of the load-bearing structures-were defined on the basis of the deterioration of the structures. In this chapter a new method for the determination of the membership values is described, which in addition to the deteriorations of the structures takes into account other parameters of the structures, and the impact exerted on the quality of the structure, too. The method is suitable for the determination of the membership values of all primary and secondary structures. As an example the membership values of the foundation structures of the buildings in the database were defined and the results were analysed. The method was elaborated by the use of "real fuzzy values" (R-fuzzy sets), an extension of the concept of classic fuzzy sets, the former being suitable for simultaneously taking into account various aspects.