The layer of waterproof material that keeps water from getting into a building is called flashing. Bitumen, EPDM, aluminum and copper can all be used as flashing materials. Flashing should be installed at roof lines, on the tops of the walls under copings, above windows and doors and below window sills. Properly installed flashing should meet code requirement for “through wall flashing”.
Through wall flashing acts like a large skirt to collect water once the water has penetrated the most exterior portion of the masonry. Then it directs the water to the outside of the building through weep holes. The absence of weep holes means there is no way for the water to escape once it penetrates the masonry wall. The absence of flashing means that once water penetrates the exterior wall, it will be directed into the living space.