Manufactured in polypropylene, the base being finished in grey, the dome cover in white. Dome fixed to base with screw into self locking brass insert. Dimensions Height 197mm Diameter of base 267mm Diameter of aperture at base 184mm Each Extra Aqua Vent can ventilate an area of up to 36m2 Method of fixing Each Extra-Aqua-Vent can ventilate an area of up to 36 square metres and will bond perfectly to asphalt, bituminous felt and plastic roofing materials. For felt roofing, first cut a hole approximately 210 mm in diameter through the base layer. It may also be necessary to cut a hole through the insulation to aid ventilation. Place the vent over the hole and dress subsequent layers of felt up the neck of the vent. The final layer of felt should then be dressed around the neck of the vent, so that the domed cap provides a weatherproof cover. For Asphalt Roofing, the sheathing felt should be cut and the vent positioned, as per the felt roofing  instructions. The asphalt should then be applied over the base and allowed to cool and set. Subsequent coats of asphalt should be dressed up to the neck of the vent, to within 13 mm of the vent holes. Solid fillets of asphalt should then be formed at the base. The vent requires no further fixing, as the waterproofing medium will hold it securely in position. Finally, secure the domed cap with the brass screw provided.