Electron Beam Melting is an innovative process for the production of massive parts with minimum support structures and negligible residual stress. However, some geometries, such as overhang volumes, still pose a challenge to manufacture and can result in non-negligible geometrical defects such as “side loss”. Based on thermomechanical simulations, the aim of this work is to understand the reasons for the appearance of this defect and its evolution throughout successive layer depositions. Simulation results indicate that side loss is due to the repetitive force applied by the new layers on the previous ones due to the fast shrinkage in the top of the part. In addition, both simulation and experimental analysis show an increase in the defect amplitude with increasing thickness of the overhang volume and its stabilization after the first millimeters of the overhang volume.