It is disclosed a building kit for erecting buildings, especially wall constructions in buildings, comprising at least two mainly parallel wall plate elements (1), where the wall plate elements (1) are equipped with a number of grooves (2) on at least one side of the elements (1), said grooves (2) having a shape so that the part of the grooves (2) lying inside the wall (1) is larger than the mouth of the groove (2) opening towards one of the surfaces of the wall (1), where it between the grooves (2) in the wall elements (1) run joining elements (4) being designed with an extended part fitting inside the extended part of the wall groove (2). It is also disclosed joining elements (4) connecting adjoining and abovelying wall elements (1).