Ventilating element comprising two extruded shells, namely an inner shell (2) and an outer shell (3), and a support (4) provided between the aforesaid shells (2,3), whereby the support (4) is provided with an air passage (5) reaching from the inner shell (2) to the outer shell (3), whereby the support (4) is built of two blocks (6 and 7) on which are respectively provided the inner shell (2) and the outer shell (3), characterised in that the two blocks (6 and 7) are telescopically adjustable.