Abstract: A ventilation cowl for arrangement on a house roof. The cowl comprises a plate-shaped member which is adapted to form an abutment against the roof and which is designed with one or more openings for the reception of air ducts. The cowl further comprises a superstructure which covers the openings and at least a portion of the plate-shaped member. The superstructure is divided into two chambers by means of a partition wall, namely an approximately closed inner chamber and an aired outer chamber. An outlet union from an air duct passes through the partition wall and empties on the outer side of the partition wall in the outer chamber. By means of the ventilation cowl condensation which has a tendency to be formed on the inner side of the cowl is readily expelled. The inner chamber can form an inlet chamber to a fan which is received in the inner chamber, so that one or more air ducts can be readily connected to the inner chamber to be served by the fan.