The document specifies a method of determining the shear strenght for out-of-plane forces fo joints between prefabricated components made of autoclaved aerated concrete (AAC) or lightweight aggregate concrete with open structure (LAC). The shear strength of longitudinal joints between prefabricated AAC- or LAC-components for forces acting perpendicular to the plane of the components is determined by applying a vertical line load along the middle-axis on top surface of a horizontally positioned component or a section there of. The loaded component is supported both longitudinal edges. At least one of these longitudinal supports consists of an adjacent component connected to the loaded component by the type of joint to be tested. The load is increased coninuously or in steps until failure of the joint.