What feature may surround flat roofs to help manage water drainage?

A parapet is a low wall or barrier that is placed on the edge of a flat roof. Its primary function is to help manage water drainage by directing water away from the roof and reducing the risk of water pooling or leakage. Parapets can also provide added safety by preventing individuals from falling off the edge of the roof and can serve as a visual barrier to conceal roof-mounted equipment from view. Proper design of the parapet can enhance water drainage systems by ensuring that any accumulated rainwater flows towards drains or other drainage locations.

In contrast, ridges are typically associated with sloped roofs, serving as the peak where two planes meet, which is not relevant to flat roofs. Overhangs extend beyond the building's walls and can provide shade or weather protection but do not specifically aid in managing water drainage on flat roofs. Fascia is a vertical board that caps the end of the roof trusses, but its function is more aesthetic and structural rather than directly related to water management. Thus, the parapet is specifically designed to address drainage on flat roofs.