The invention relates to a method for producing a flat element (2) for vehicle bodies according to the sandwich construction technique. Said flat element comprises an outer cladding (4) and a hump plate (6), with edge sections (8, 10) located between them. According to the inventive method, a first step consists of at least partially bonding the edge sections (8, 10) to the hump plate (6) using a mechanical joining process. A second step consists of bonding the hump plate (6) to the outer cladding (4) by adhesion and a third step consists of at least partially joining the edge sections (8, 10) to the outer cladding (4) using a mechanical joining process. These measures result in a flat element with a high degree of transversal resistance and resistance to buckling.