The requirements for modern brick masonry have grown steadily in the past. In addition to the architectural requirements for user flexibility and aesthetics, they must also be optimally designed in terms of the structure, energy, sound insulation and fire protection. The complex combination of the above-mentioned criteria often leads to the fact that the structural design of buildings made of brick masonry is only possible with great effort or with a hybrid construction method. Conservative linear design methods prove to be incapable of exploiting the available load-bearing reserves. The solution appears to be the application of modern nonlinear deformation-based verification methods. Although these methods provide a more realistic representation of the load-bearing behavior of masonry, they also impose increased requirements on the calculation model and the masonry-specific design principles. In practice, the design principles are criticized, among other things, because of the very simplified modeling assumptions and the resulting inadequate representation of the interaction effects within the building structure when determining the internal forces. Moreover, the application of the design concept according to DIN EN 1996-1 in connection with the validity of the shear failure criteria is to be questioned. Furthermore, important details of the structure, such as the reduced slab support at the energy-optimized wall-slab node, have not yet been considered in the codes. The exploitation of existing load-bearing capacities by modifying masonry-specific rules is of essential importance for the future viability of masonry as a building material. The present work investigates the load-bearing and displacement behavior of unreinforced brick masonry with special attention to the influence of wall-building interaction. For the investigation, a nonlinear three-dimensional micromodel is developed, which can represent effects in the wall plane as well as out of the wall plane. With the help of the numerical model, a comprehensive variant study is carried out, considering all the main parameters influencing the shear-bearing behavior. The consideration of a variable moment distribution over the wall height as well as an eccentric vertical load introduction due to partial slab support at the wall head is of particular importance. To investigate and differentiate the decisive failure mechanisms at wall level, the stress and strain states at both joint and individual brick level are analyzed, and the capacity curves are evaluated with respect to load-bearing and displacement capacity. Next, the obtained knowledge will be used and incorporated into an improved design approach, which should enable the correct representation of the horizontal load-bearing capacity with a simultaneously manageable computational effort for the practical application in construction. Finally, the development of a macromodel for the simulation of masonry shear walls with and without eccentric vertical load introduction at the wall head is described.