An example of vulnerable roof areas and a recommended fix. The typical vulnerable areas are where the roof changes direction or material (for example, AREAS where the roof meets a chimney or a wall). On a properly installed roof, these areas are flashed. Particularly vulnerable areas exist where two or more flashings intersect, for example where a chimney occurs in a valley. Things that obstruct the flow of water off sloped roofs increase the risk of leaks. Skylights, chimneys and dormers are examples. Roof penetrations for plumbing stacks, electrical masts, etc. are also weak spots.