The contemporary construction, both new buildings and renovations, is characterized by the low air permeability of the building envelope. The high airtightness of the building envelopes reflects current energy-saving trends. However, saving energy is a contrast with hygienic conditions (supply of fresh air). The well-being of occupants is defined by the interaction of the physical, chemical and biological components of the internal environment of buildings. The basic factors of indoor air quality are indoor air temperature [°C] and relative humidity [%]. The paper includes an analysis of long-term (1-year) measurements in the apartment in terms of the thermal-humidity microclimate, including the optimization of the hygro-thermal parameters of the indoor environment. The measurements were carried out in a standard apartment in the residential prefabricated building after revitalization (new thermal insulation and new windows) located in Central European climatic conditions. This climate is typical of low relative humidity in the indoor environment of buildings in the winter (heating season).