Numerical heat, air, and moisture (HAM) models enable powerful predictions of the hygrothermal behavior of building components. While the embedded formulations of the transfer equations and boundary conditions are largely physically equivalent, deviations amongst different models might still occur, due to different assumptions, simplifications, and approximations in implemented material properties, boundary conditions, etc. This paper presents results of an empirical round robin validation, in which the hygrothermal responses of wall assemblies under controlled boundary conditions are simulated by different models. Participants are assumed to be “engineers”, lacking dedicated measured material properties but applying technical sheets from the manufacturers. Material properties can thus be determined from built-in databases or generated from available datasheets. Boundary conditions are known, while non-specified surface transport coefficients can be derived from standards or from experience. The confrontation to the experimental datasets is used to validate the models’ robustness by similar trends. “Result overlapping” indicates the inherent differences of the models. User preferences, biases and/or mistakes in implementing material properties and surface transport coefficients are found to yield disparity or even incorrectness. Despite the significant deviations in implemented material properties and surface transport coefficients, heat-related outputs express considerable similarities, while moisture-related outputs show larger disparity.