What is a parapet?

What it is

Walk to the edge of a commercial flat roof and you meet a knee-high or waist-high wall: that is the parapet. It exists for several reasons at once. The building code's reason is fire: the IBC, Section 705.11 requires parapets on exterior walls that need a fire-resistance rating, with exceptions, and requires them to carry the same rating as the wall and to rise at least 30 inches above the point where the roof surface meets the wall. Beyond the code, a parapet hides rooftop equipment, gives the roof edge a finished line, deflects wind that would otherwise peel the membrane, and stops a worker from stepping off.

Its parts matter more than its height. The top is closed by a coping — metal, stone or precast — that sheds water to the roof side. At the bottom, the roof membrane turns up the inside face as base flashing, and a counterflashing or the coping itself laps down over the top of it. Through it, at intervals, scuppers let the roof drain. The IBC's roof chapter covers the flashing and coping requirements, and on houses the IRC's flashing rule, Section R903.2 names intersections with parapet walls specifically.

What it costs and who does it

Parapet work is priced by the linear foot of wall: new metal coping, repointing or rebuilding masonry, replacing base flashing and counterflashing, adding or clearing scuppers. It is shared between trades — a mason for the wall and stone coping, a sheet-metal shop or roofing contractor for metal coping and flashings, and the roofing contractor for the membrane's turn-up — and on a re-roof the flashing side is part of the roof price. The directory's flat-roof replacement cost guide explains how perimeter details are estimated within a replacement.