a method for producing a composite construction element comprises the steps of : a ) providing a composite construction element , which comprises a thermoplastic core layer between two fiber - reinforced thermoplastic cover layers ; b ) providing one or more interruptions in a fiber - reinforced thermoplastic cover layer of the panel ; c ) positioning a fiber - reinforced thermoplastic reinforcing layer over and / or near the interruption ; d ) deforming situated along the interruption and , if desired , the thermoplastic reinforcing layer , preferably while simultaneously locally compacting the core layer , so that a thermoplastic construction element having a recess which is delimited by fiber - reinforced thermoplastic walls is obtained .