Flavent Single Piece Breather Vent - Bitumen Flange This is a single piece breather vent from Flavent, with a bitumen flange - the bitumen skirt is 500mm x 500mm. The breather vent has been designed to help improve ventilation within modern buildings, by creating air circulation above the insulation layer. It allows cool air to enter the air space, and warm moist air to exit the air space. The breather vent removes moisture that is trapped within a flat roof, which helps to prevent the formation of condensation on the underside of the waterproofing layer - this is often how blisters, mould and rot occur. Dimensions Height: 345.5mm