Centering for casting concrete roofs

In a centering for casting concrete roofs, comprising a rectangular steel construction including at least two longitudinal girders and a plurality of cross beams welded thereto in spaced relationship to support a flat form board, the improvement in which each one of said cross beams, at least at one end thereof, is provided with an extension arm displacable in the transverse direction of the centering, said arm slidably engaging the cross beam in a manner such that its upside lies flush with a geometrical plane toughing the top surfaces of all cross beams, and said arm being displacable with its end outside of the end of the cross beam to support a form board, the width of which is larger than the nominal width of the centering, each one of said cross beams consists of a pair of channel irons welded in spaced relationship to the longitudinal girders with their webs facing one another and with the flanges turned outwards, and the extension arm is in the shape of a square tube arranged at each end of each one of said cross beams within the space between the webs of the channel irons, said arms being displacable with slip fit in the longitudinal direction of said cross beams, the length of said square tube being maximum half the length of said cross beam, its width corresponding substantially to the width between said channel irons, and its height being substantially equal to the height of said channel irons, each square tube at the bottom side of the end thereof projecting into the space between the channel irons, is provded with a plate welded thereto, said plate having a greater width than the space between the channel irons, and a flat bar steel is welded over the extreme ends of the bottom flanges of said channel irons to form a stop member for engagement with the plate on said square tube.