Abstract: A water-excluding vent structure wherein water impinging upon an outer surface thereof is excluded while air is allowed to freely flow through the vent structure to an internal space. The circular or other appropriate shaped vent structure has a series of parallel louvers designed for orientation in a level, horizontal plane. A porous, polypropylene membrane is placed behind the louvers. A perimeter gasket is used to seal the vent structure to the object to be ventilated. A notch is formed in an inner edge of the perimeter gasket along a line which is a perpendicular bisector of the louvers. The space defined by the notch is communicative with a drain hole in the outer housing. When properly oriented with the notch in a lowermost position, any moisture passing through the porous membrane collects in the notch and flows through the drain hole.