It is vitally important to understand the moisture transfer process in the buildings as this knowledge allows to generate solutions on how to control it. The data about typical indoor air humidity levels and moisture sources are usually taken from the existing standards. However, this information needs to be verified and adapted for the local situation as occupant behaviour varies for each country. Similar studies have been performed in Estonia and Finland and they indicate that the typical data of these northern countries differ from the one provided in the standard. This paper presents the preliminary results of moisture measurements for several residential and office buildings in Latvia. Afterward, the difference between indoor and outdoor air absolute humidity is calculated and the data is analyzed depending on the outside air temperature. The results can be used to provide suggestions on the adaption of EN ISO 13788:2012 Figure A.2 which presents the information on the variation of internal humidity classes with external temperatures. The study is not yet completed as more measurements must be taken since the outside temperatures have dropped under zero degrees only for a few days and the number of the test objects must be increased.