On-site assessment of hygric and thermal performance of an interior thermal insulation system on the basis of hydrophilic mineral wool is presented in the paper. The system is applied during the Summer period oil a brick-built house from the end of 19th century. Hygrothermal testing is done during the time period of 4 years. The reconstructed building envelope exhibits very good hygrothermal performance. The thermal resistance increases approximately two times. Water condensation is never observed inside the envelope during the whole testing period. A comparison with the previous experiment in semi-scale conditions which was performed for similar insulation system constructed during the winter season shows that the precedence should be given to the application of the system in summer period as it is more considerate to the old masonry. (C) 2008 Elsevier B.V. All rights reserved.