In recent years, questions emerged about how high level moisture contents might affect heat technical properties of building materials. Yet, existing standards and scientifi c publications, respectively, do not provide conclusive insights into the area of high rated moisture, since they are valid for the equilibrium moisture area only. Taking instructions of calculation according to harmonized European standards (EN ISO 10456, DIN EN 1745) as a basis, typical moisture contents of freshly produced AAC would theoretically involve immense surcharges on λ, which would drastically affect thermal conductivities and, in turn, increase heating costs. Moreover, increasing risks of mould formation and other damages would be expected. Our experiments clearly demonstrate that actual increases in λ at production moisture levels are far below values stated in the European standards. In addition to this fundamental perception recent investigations have shown that the surcharge of moisture content under typical condition of AAC use in buildings the moisture conversion factor Fm is not higher than 5%. In several investigations a lower value for Fm have been found and can be used in the future for starting points of further investigations and tests.