The uniform method for soil gas radon measurements (Neznal et al. 2004, Barnet et al 2008) is used by all Czech organizations dealing with building site assessment (list of them is given on web of the State Office for Nuclear Safety ). The soil gas sample is taken from depth of 0,8 m using probes with the „lost tip“. At least 15 measurements are performed at the building site. The 75% quantile of radon data set serves as an input parameter for radon index classification. Permeability is determined from the grain-size analysis, expert evaluation or in situ permeametric measurements. All subjects dealing with soil gas radon measurements pass the calibration of devices in the radon chamber of the National Institute for Nuclear, Chemical and Biological Protection and the field testing at the reference sites to ensure the comparability and reliability of sampling process, which is organized by the Charles University in Prague, Faculty of Science.