The investigation of the need for three‐dimensional hygrothermal simulations. This article discusses the question of whether transient, two‐dimensional simulations are sufficient for the hygrothermal analysis of a three‐dimensional detail, such as the supports of a wooden beam ceiling in an internally insulated wall, or whether three‐dimensional simulations should be carried out. The validation of the software DELPHIN 6 is shown with the help of a three‐dimensional, stationary test case from EN 10211, subsequently followed by a very good correlation between measurement and simulation output. This has been determined based on the detailed measurement results from beam supports. From the thermal point of view, no more precise results can be achieved by the three‐dimensional calculations, however, the hygric results are somewhat better reproduced by the three‐dimensional calculations. For planning real tasks, two‐dimensional simulations should be sufficient, provided that the simulation settings are selected within the secure margins.