The maintenance and renovation of old (over 100 years old) residential buildings is one of the priority tasks in the last decades, because - especially in the inner areas of big cities - there are still a lot of them today, and therefore it has a decisive effect on the quality of life of many people. Since the structural design, materials, and condition of these types of residential buildings show many similarities, it is advisable to develop a uniform method for their condition assessment. A condition assessment and decision support model that is suitable for objective and uniform evaluation of this large number of old residential buildings and enables their energy-efficient maintenance and renovation as needed is being developed. The decision model consists of 4 main components (“Project info”, “Knowledge base”, “Preparatory work process”, “Fuzzy system”). For this method, a fuzzy signature-based decision model was developed, that can be used for the condition assessment of old residential buildings and for multi purpose intervention decision support. In this article, the main components are briefly overviewed and the automatic relationships between the individual elements of the project info and how it’s values affect the structure of the fuzzy signature is examined in details. Since the optimal structure of the fuzzy signature helps to make the right decision and the ideal use of the available resources, it is of great importance in terms of energy efficiency and sustainability. The other aim of automation is to make condition assessment even faster and more reliable.