The DLS Pro-Tile roof cowl and vent has been designed to give a free area ventilation of at least 20,000sqmm required by EN 721, if installed correctly. The Ceiling Vent & Roof Cowl are supplied as a complete kit. The roof cowl contains an adapter that should be sealed and fixed with screws (not supplied) to the roof of the caravan and is then covered with a cowl and fixed with the cowl screws (supplied). The cowl is fitted over a box section that is constructed between the ceiling and the roof. (Box section hole required ID 195mmsq).