Configuration of louvers directs passage of water from cavity to outside of building, while inhibiting reverse passage of water. Design permits air passage into cavity, thus aiding pressure equalization and reducing suction which can cause water penetration. Rectangular closure strip prevents mortar droppings from clogging openings. #343 has compressible flanges that can accommodate joints widths of 1/2” - 3/4”. Stocked for modular brick only in grey color.