The answer to 'types of flashing' is that flashing is a thin, impermeable material used to prevent water from entering a building at roof-wall intersections, chimneys, dormers, and other areas where the roof meets another surface. The main types of flashing include step flashing, counter flashing, valley flashing, and chimney flashing.
Step flashing is L-shaped and installed along the joint where a roof meets a vertical wall. Counter flashing is installed over the top edge of the step flashing to prevent water from getting behind it. Valley flashing runs along the low point where two roof slopes meet, and chimney flashing seals the area around a chimney penetration.