Radioecological monitoring of radon-hazardous territories in residential and public buildings of the towns of Lermontov (Russia, Stavropol Region) and Baley (Russia, Transbaikal Region) made it possible to reveal that the volume activity of radon in premises on 1 floor of buildings reliably characterizes the radon inflow from the soil surface. This control parameter, which can be used to estimate the radon danger of the territory, to make decisions on the sanitary condition of the building, to estimate the potential danger to the population or personnel, to calculate the potential dose rates. Improvement of radio-ecological monitoring in potentially radon-hazardous areas is aimed at monitoring the volume activity of radon on 1 floor of buildings, the excess of which is higher than the normal values is the basis for making managerial decisions to protect the population or staff. © The Authors, published by EDP Sciences, 2020.