This study investigates four numerical models to approximate the static and dynamic resistance of an unreinforced masonry wall loaded in one-way out-of-plane bending. From validation with experimental data it was found that for the combination of shell and interface elements with discrete cracking the static and dynamic behaviour of unreinforced masonry walls for out-of-plane bending is dependent on the interface stiffness. Due to Euler-Bernouilli's hypothesis, on which these elements are based, the deformation over the thickness remains straight, while in reality the wall deforms non-linearly over the thickness. A reduction of the interface stiffness is proposed to mimic crack opening with a linear deformation and obtain realistic results. The validated model is used for comparison with the analytical calculation of NPR 9998. This shows that the boundary condition assumptions can be made differently to increase the resistance of out-of-plane walls.