Abstract: A construction system comprises a lattice girder reinforcement and a formwork for producing double-skinned concrete ceiling or wall slabs, with two frames separated from each other. The rising reinforcement of the inner skin is bent towards the outer skin so that the top inner skin support edge remains undisturbed and extends to the top outer skin edge. It comprises a reinforced haunched concrete slab each end of which defines a slot through which an interconnecting tie bar extends. Abutting prefabricated slabs are aligned with respective connecting bars inserted into slots and joints between two abutting wall elements. A board with an open hole is slid on the rear end of the connecting bar and bears on the other surface of the wall elements and a turnbuckle at this end bears on the free surface of the board.