The significance of sound insulation and noise protection is contingent on the utilization of thermal insulation and the implementation of lightweight construction methodologies. In both scenarios, sound transmission is predominantly characterized by a deficiency in mass. The materials employed for thermal insulation are often inadequate for sound insulation and noise protection purposes. Moreover, the presence of leaks in the building envelope, including connections such as windows and doors, serves to facilitate sound transmission within the building, thereby compromising the effectiveness of the building envelope’s sound insulation. This study undertakes a comprehensive analysis of noise protection in lightweight construction, employing a case study approach. The subject of the study is two neighbouring detached houses, constructed on two storeys and insulated with a external thermal insulation composite system. The sound transmission through the staircase in one of the houses results in a discernible background noise in the neighbouring house. A innovative methodology is employed to analyse the causes of the sound trans-mission observed in the staircase of the transmitter house in the receiver house. The conventional measurement method has been proven to be inadequate in this context, as it does not allow for differentiation between the various potential causes. For instance, it is not possible to determine whether the sound is transmitted through windows or connections. Consequently, the investigation is continued with an acoustic camera, which allows for the visualisation and localisation of the sound waves and sources.