The analysis of the current codes for the insolation in apartments has been done by the authors. It is shown that the insolation assessment during exposure is not sufficiently correct. The current codes do not take into account the amount of solar energy, the transmittance of UV radiation with double-glazed windows, the dimensions of light openings and the room parameters. The current codes for insolation do not contain requirements for the essential level of sanitation. The proposed energy method of calculating insolation corrects the shortcomings of the existing Sanitary Codes method considering the climatic and structural factors. It introduces an unambiguous quantitative measure of insolation-the dose of UV radiation as well, which provides a given level of bactericidal efficiency of room sanitation. Additionally a proposal to specify the bactericidal efficacy level of irradiation based on the most common microorganisms in living rooms (Staphylococcus aureus and Escherichia coli) has been made. An example of the UV radiation dose calculation in rooms is given, which provides a necessary level of bactericidal efficiency.