In Budapest, several buildings of historic value have been renovated and refurbished in the last 10 years. Among them two buildings of high historical prestige are presented in the paper: the 159-year-old palace building of the Hungarian Academy of Sciences, which is under renovation, and the Eiffel-designed 152-year-old steel hall of the MÁV Vehicle Repair Plant, which has been refurbished into the Eiffel Art Studios of the Hungarian Opera House. Both buildings were originally designed and built without standards and regulations, using the technical and technological knowledge of the time, and each of them has interesting and unusual technical solutions. The load-bearing structures of the buildings had problems in verifying that they met current standards. The reconstruction works were designed by KÖZTI Architects & Engineers. Scientific and technical support was provided by the Department of Structural Engineering of the BME by expertizing the buildings, adapting the standard loads to the current site and analysing the behaviour of the load-bearing structure by advanced models. The paper describes the buildings, the technologies and scientific methods used in their renovation/refurbishment, which finally ensured the safety of the structure to the current requirements.