Thermal performance of buildings is the key aspect of energy saving and energy efficiency enhancement. The thermal behavior of a building is formed under the influence of many factors. The complexity of the process of heat transfer through envelope structures makes the problem of multifactorial assessment of thermal behavior in building envelope elements crucial. This paper presents an assessment of the heat-insulating effect gained from the use of the “ceramic microspheres – binder” composite coating as additional thermal protection of the combined unventilated covering of a building. This multifactorial assessment is based on the calculation method of measuring thermal behavior in building envelope elements developed by the author. It was shown that the application of the composite coating has almost a zero heat-insulating effect and does not provide a normalized level of thermal performance of the enclosing structure during the cold season. In the meantime, the application of mineral wool slabs as the traditional heat insulation for the basic construction allows enhancing thermal properties of the construction to a specified value. Such heat insulation is best for the building thermal capacity, providing a minimum heat gain during the warm season.