A mounting box for installation on an exterior wall of a building. The mounting box has a box-shaped structure having a substantially horizontally disposed top surface when in situ, a nailing flange around a perimeter of the box-shaped structure, a downwardly and outwardly inclined shoulder on each side of the top surface, the shoulders each having a shoulder surface and a plurality of notches along an outer edge of the shoulder surface which attract and constrain the flow of water along the shoulders.