Which wall structure extends above the roofline and provides a parapet-like effect?

The structure that extends above the roofline and provides a parapet-like effect is a parapet wall. Parapet walls are common architectural features typically found on flat roofs, serving to protect the roof's edge, prevent falling debris, and provide a safety barrier. Additionally, they can be aesthetically pleasing and can contribute to the overall design of a building.

Parapets often facilitate drainage and help redirect water runoff, which is vital in maintaining the integrity of the roof structure. This wall extends vertically, beyond the roofline, distinguishing it from other types of walls that do not serve the same function or may not rise above the roofing surface.

In contrast, a party wall shares a boundary between two adjacent properties and is usually not designed to extend above the roofline. A boundary wall defines the perimeter of a property but, like the party wall, typically does not rise above the roofing structure. Support walls, on the other hand, are structural walls that carry loads but do not provide the distinct parapet effect as they are primarily designed for structural integrity rather than for aesthetic or protective purposes.