Parapet

Plain-English definition

The part of a wall that extends above the roof line — the low wall you see around the edge of most flat-roofed commercial buildings. The International Building Code defines it simply as “the part of any wall entirely above the roofline.”

Why it matters to you

Verified: Parapets are where the roof system, the wall system, and the weather all meet, and building-enclosure specialists single them out because the water, air, and thermal control layers of two different assemblies must connect there without a gap (IIBEC Interface — parapets). Unlike an ordinary wall, a parapet is exposed to the weather on both sides, and gaps in its air barrier can pull moist air into the assembly and cause condensation damage that shows up as a “roof leak” (GAF — parapet control layers). For an owner, that means parapet copings, base flashings, and counterflashings deserve specific attention in every inspection — a stained parapet wall is a finding, not a cosmetic issue.

Technical detail

Good parapet practice runs top-down: a coping cap sloped back toward the roof so water sheds onto the membrane rather than down the building face; membrane base flashing turned up the parapet and terminated with flashing/counterflashing detailed to allow differential movement between roof and wall; and continuous water, air, thermal, and vapor control layers carried across the transition. Parapets also interact with wind design — a flush roof edge with no parapet provides the least wind-uplift protection at the edge, and perimeter edge metal and copings are covered by their own securement standard (ANSI/SPRI/FM 4435/ES-1).