In the article, the authors presented the results of microbiological air quality studies in selected buildings with additional thermal insulation applied from the inside using a silicate and lime system, as well as the results of a survey study concerning the comfort of use of said buildings. The microbiological air quality studies, conducted in buildings immediately prior to and after the application of additional thermal insulation using silicate and lime sheets, demonstrated a significant decrease in the number of mould spores in interior spaces. This was also reflected in the results of a survey study. The survey study was conducted with users of public and commercial buildings and municipal housing buildings in Krakow. Thanks to the additional insulation applied from inside using the silicate and lime system, all of the utilitarian parameters of internal spaces had improved. The most significant changes concerned parameters like comfort of use, the aesthetic of the spaces and breathing comfort. According to experts, the silicate and lime system was also rated highly in terms of the analysed parameters.