The paper is devoted to the study of the regularities of the radon situation formation in modern multi-storey buildings at the design stage. Calculation schemes for radon entry into the premises of the lower and upper floors are constructed, a method for determination of radon concentration in the building after its erection is proposed. It is based on a joint analysis of the soil base physical and mechanical characteristics of and the design features of the underground shell of the building. According to the calculations results, a significant role of air exchange in the formation of a favorable radon situation in the building was noted.