A development project was undertaken within the consortia formed by Polygon and AK-konsult. The aim of this project was to map out the impact of humidity leakages on the result of humidity measurements in concrete slabs according to the so-called RBK-method. It is behind the idea of this development project that the main purpose of this thesis can be derived from. For instance, an evaluation of already existing data material from a RBK-measurement has been done. A method has been retrieved in order to compare the trend of the measured values of the relative humidity with the trend of the expected values of the relative humidity during the drying process. The main goal has been to implement this method as an instrument to analyze the actual drying process. A survey study was undertaken among the employees of the consortia in order to point out the differences that arise during the installation of the measurement equipment prior to measurement according to the RBK-method. The result of the survey has been summarized and analyzed in purpose to catch a wider glimpse over the different kinds of variables that might have an impact on the result from a RBK-measurement. The outcome from the study of the existing measurement data shows that some of the measurement spots tends to dry out faster than the calculated drying process, while other spots indicates a slower drying process. Three of them actually pointed out that they were under humidity, which implies that they still hadn’t reached the stadium of moisture equilibrium with the concrete. The main reason behind the observed discrepancies might have its explanation in the fact that measurement wholes that have been subjected to a big humidity leakage. The consequence of measurement spots subjected to big humidity leakages, is that the measured value of the relative humidity turns out to be much lower than the actual level of the relative humidity in the concrete. An observation has been made in the plausibility analysis and in the Vaisalaproject that the normative equilibrium time exceeds the number of three days that’s been ordained by RBK. A further study of the normative equilibrium time can thereby be recommended to clarify if it still can be compatible with the different kinds of concrete classes of today.