Preserving cultural heritage in seismic territories like Italy requires effective strengthening techniques to restore masonry walls in-plane shear resistance and prevent out-of-plane overturning. The seismic performance of masonry structures and reinforcing systems is typically assessed through experimental tests and numerical modelling. Shaking table tests provide reliable experimental simulations of earthquake effects. Given the small dimensions of shaking tables, it is often necessary to design specific tests on individual structural elements like masonry walls, arches, and vaults. However, designing accurate boundary conditions for these tests is challenging, particularly within a blind prediction framework for out-of-plane mechanisms in unreinforced masonry buildings. This study adopts a blind prediction approach to develop accurate boundary conditions for finite element models (FEM) of unreinforced masonry walls, focusing on their seismic response with respect to out-of-plane mechanisms. A critical type of orthogonal interaction is addressed, i.e. C-shaped walls at building ends. Characteristics of masonry walls and floors typologies are determined based on the primary construction technologies of architectural heritage in Italy, with particular reference to Sicily.