This article presents a method that can be used to convert soil properties into building physical material properties that meet the requirements of modern codes for transient hygrothermal simulations. The soil input data must be specified by the so-called "van Genuchten parameters" in order to predict the water retention curve and the hydraulic conductivity of unsaturated soils. The percentages of silt, sand and clay are used to calculate the moisture-dependent thermal conductivity for soils with different water saturation. The output is a validated set of hygrothermal material functions (moisture storage function, liquid water conductivity, water vapour conductivity, thermal conductivity), which is prepared for use in simulation projects or for inclusion in a database. The methodology described in this document has been implemented in an MS Excel tool that enables an efficient, almost fully automatic conversion of a list of soils in three steps.