Using coastal buildings for the emergency evacuation process in an unexpected tsunami event is an effective measure in flat widespread coastal areas. This is especially true in countries such as Japan located adjacent to the faults of tectonic plates, and having only a very limited time frame for evacuation following a tsunami warning. Well-constructed tsunami evacuation buildings can play a vital role under such circumstances. This makes proper understanding of tsunami force and its variation in different building configurations vital in the engineering design of such buildings. In this study, we assessed tsunami force estimation methods for buildings consisting of openings. We also discuss the influence of their internal configurations and orientations for incoming tsunami flow based on physical model experiments and numerical simulation and analysis. Results indicated that the arrangement of internal building configurations with large openings is important in estimating tsunami force, and that building orientation related to the direction in which the tsunami approaches also affects tsunami force, mainly due to the change in effective area directly facing the tsunami.