A roof air-vent pipe (D) has a projecting dome (9) on the top side of a metallic roof-covering plate (1) and a vent pipe (7) carried by the dome over a cap (19). In order to obain a roof ventilator which is particularly efficient in use, the plastic dome which carries a plastic vent pipe (7) is set on the marginal area (8) of a hole (2) cut out in a roof-covering plate (1).
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