The urban-type residential houses built before World War Two represent a large part of the built environment in Hungary. Due to their physical condition and low energy-efficiency the retrofit of these buildings is very much advisable nowadays. In this paper we propose an approach based on fuzzy signatures and state machines, that helps decision support for determining the renovation scenario concerning necessity, cost efficiency and quality. Using the knowledge obtained from diagnostic surveys done during the previous decades by architect experts, and technical guides and the available database of contractors billing, a protocol for the preparation for optimized refurbishment is proposed, based on the concept of an extended fuzzy state machine model. In this combined model the theoretical concepts of finite-state machine and fuzzy state machine, and also the principles of fuzzy signatures are applied. © Springer International Publishing Switzerland 2014.