Parapet walls are similar to taller walls with a couple of minor exceptions. If the parapet wall is relatively short, the base flashing may extend up and over the top of the parapet wall and drape over the outside face. The counter flashing often is extended to form a coping or cap for the top of the parapet wall. The outside face of the coping also forms the drip edge flashing. Coping can also be stone, concrete or terra cotta.
Another possible difference with parapet walls is the presence of through-wall flashings. It is recognized that parapet walls are exposed to wind-driven rains from both sides, and these walls get considerably wetter than conventional exterior walls. Since most walls are porous, it is recognized that water will enter the wall system.
It is common to provide through-wall flashings just above the counter flashings for the roof on high-quality parapet walls. Further, through-wall flashings are sometimes provided just below the coping to ensure that any water that gets into the top of the wall cannot find its way down into the building. It should be understood that these high quality details won't often be found residentially.
Clad the Parapets
Good quality roofing work often includes a metal cladding on masonry or concrete parapet walls on the inner or (roof side) of the parapet. The entire height of the parapet wall is protected from wetting with metal. With single-ply roofing systems, the parapet is protected by the roof membrane itself, extended up the wall. This minimizes the need for through-wall flashings. It may also prolong the life of the masonry. Where this is seen, you are usually looking at high quality work.