A series of tests on the moisture expansion of vertically perforated clay units from all regions of Germany were carried out in 2022 to verify the range of values given in the German national annex to EN 1996-1-1. Tests were carried out on the basis of EN 772-19 (relevant for horizontally perforated units). The obtained data confirm the given range of values in the German national annex. An additional series with selected specimens was carried out to determine the moisture expansion under laboratory conditions in climate 23°/80% r.h. These values are compared with the results of the standard tests and results from literature. Moisture expansion of vertically perforated German clay units can be neglected under practical conditions. The necessary work for a possible revision of testing moisture expansion with respect of conditions of the building site is discussed.