In the present paper we propose a solid theoretical framework for the automatic parametrization of the cost-optimal refurbishment of arbitrary buildings. The parameters describe the structural parts of the building that can be modified or replaced during the refurbishment process. The methodology also provides the cost-optimal refurbishment cost and the corresponding smallest possible total life-cycle operation cost constrained by the available technological and economical limitations. The theory is implemented into the EnergOpt expert system providing fast and accurate answers to costoptimization problems appearing in common practical applications. The system is built on firm mathematical foundations that is supported by state-of-the-art optimization algorithms capable of finding good optimums in a short amount of CPU time. The modular structure of the IT implementation facilitates effortless localization in different countries. The application of the system may considerably contribute to the decrease of the heating energy consumption and the corresponding environmental load of the building stock. The practical potential of the technology is demonstrated by the energetic analysis of an existing family house. © (2014) Trans Tech Publications, Switzerland.