Heat, air and moisture (HAM) models allow efficient simulation of the building components’ hygrothermal behavior. However, specific model assumptions, simplifications and approximations, as well as users’ preferences, biases and mistakes in the implementation of material properties, boundary conditions, etc., may yield divergences among results from different models. The lack of a standard framework for HAM model quality assessment results in inconsistent benchmark cases and assessment methods in previous studies. Thus, this state-of-the-art empirical round robin validation targets to test the robustness and the reliability of HAM models in predicting one-dimensional hygrothermal responses of building components under controlled boundary conditions. It ran from 2023 to 2024, was coordinated by KU Leuven, and achieved participation of 38 groups from 19 countries. A comprehensive experimental dataset serves as “correct answer”, and simulation results from other participants form “reference answers”. Since the boundary conditions are simple and explicit, the material properties’ implementation has the main impact on the simulated hygrothermal responses. Most models prove to be robust, particularly in the heat transfer prediction. The moisture transfer prediction, on the other hand, looks more challenging. Reliability is also achieved by most models, as the deviations between simulation and experimental results are reduced when actual measured material properties are implemented as input. However, inappropriate and/or incorrect implementations are observed even with a limited impact in this case. More in-depth investigations are performed for a better understanding of HAM-simulation tools and achieving their better performance in predicting and interpreting the hygrothermal behavior of building components.