Rain Penetration (also known as "penetrating damp") is a common form of dampness in buildings. It can occur through walls, roofs, or through openings (e.g. window reveals). Water will often penetrate the outer envelope of a building and appear inside. Common defects include: * Roof defects such as faulty flashing, cracked or missing slates or tiles. * Faults in the brickwork or masonry such as missing or cracked pointing. Porous bricks or stones. * Missing or defective mastic around windows and doors. * Blocked weep holes. * Missing or defective trays in cavity walls.