Final answer:
Valley flashing is used where two roof planes meet and features a splash-diverting rib to direct water away from the roof.
Step-by-step explanation:
The kind of flashing that consists of strips of copper or galvanized steel and has a splash-diverting rib down the center is called valley flashing. This type of flashing is specifically designed to be installed in the valleys where two roof planes meet. The rib, or center crimp, helps to direct water away from the roof and into the gutters, preventing water from pooling and potentially leading to leaks.
Counter flashing is the kind of flashing that consists of strips of copper or galvanized steel and has a splash-diverting rib down the center. It is usually used to protect vertical intersections between a roof and a chimney or wall. The purpose of the splash-diverting rib is to prevent water from entering behind the flashing and causing damage.