Hygrothermal building component simulation requires a complete set of storage and transport functions. Such functions are typically determined by the aid of material models defining a set of functions that are adjusted to basic material data. Basic material data consists of either single parameters or measured functional courses of, for example, water uptake or drying. For parameter adjustment during material modeling, functional courses are most reliable. For a simple comparison of material properties, though, single number material parameters are more appropriate.

The drying behavior of building materials is rather complex, which is the reason why a single-number drying coefficient does not yet exist. Some first attempts to standardize drying data have been made. However, these did not yet result in a consistent drying coefficient definition.

The paper briefly introduces the different dependencies of the drying process. Data from experimental and numerical investigations is provided and discussed. On this basis, a new drying coefficient for building materials is defined. This coefficient is ultimately discussed with regard to its meaning as well as its additional information content compared to other moisture transport
coefficients.