Abstract: A hollow concrete building block is provided having physical characteristics which diverts water penetrating inside the block away from the interior of the building. The block comprises parallel interior and exterior walls and at least one transverse vertical web spanning between the walls to form a unitary block with an interior cavity. The webs have notches on the top and bottom surfaces which divert any infiltrating water into the cavities. The notches span the length of the top and bottom surfaces of the web. The apex of the top notch is proximate to the exterior wall of the block while the apex of the bottom notch is proximate to the interior wall. Once in the cavities, the water drops to the lowermost block where conventional flashing and weep holes convey the water to the exterior.

Abstract: A hollow rectangular concrete building block is provided having features which prevent and impede the infiltration of water into and migration of water through the block. The hollow block conventionally includes parallel interior and exterior vertical walls with at least one transverse vertical web spanning between the walls to form a unitary block with an interior cavity. Migration of water from the exterior to interior is impeded by a plurality of vertical ribs protruding from each side surface of the web. Water which has penetrated into the block cavity is redirected downwardly, as it trickles across the web, by the ribs to be ultimately expelled at the base of the block array with conventional flashing and weep holes. Grooves in the upper surface of the webs prevent migration of water along the upper surface and redirect the water to flow downwardly along the side surfaces of the web.