Scupper — Flat Roof Parapet Drainage Opening Explained

A scupper is an opening in a parapet wall, curb, or roof edge that allows water to drain from a flat or low-slope roof surface to the exterior or into a conductor head and downspout.

What It Is

On flat or low-slope roofs enclosed by parapet walls, water has no open edge to flow off. Scuppers provide escape paths through the parapet at the roof surface level. They are rectangular or round openings lined or sleeved with metal — typically galvanized steel, copper, or aluminum — that penetrate the wall and extend beyond the face of the building to discharge water.

Scuppers serve two functions. Primary scuppers handle routine drainage and connect to downspouts. Overflow scuppers are positioned slightly higher and activate only during heavy rain or when primary drains are blocked, providing emergency drainage that prevents catastrophic ponding and structural overload. Building codes typically require both primary and overflow drainage provisions on flat roofs, and overflow scuppers set above the normal drainage level are a common solution.

The sheet metal scupper sleeve and its flashing are critical waterproofing elements. The roofing membrane must integrate continuously with the scupper sleeve to prevent water infiltration into the wall assembly behind it.

Types

Open scuppers extend through the parapet and terminate flush or with a slight projection, discharging water directly down the building face. Conductor head scuppers feed into a box collector that connects to a downspout, keeping water controlled and directed away from the wall. Overflow scuppers are sized and positioned independently from primary scuppers and are set at a height that only admits water when primary drainage is overwhelmed. Through-wall scuppers penetrate masonry or concrete parapets and are factory-fabricated or field-fabricated from sheet metal with a flanged face plate.

Where It Is Used

Scuppers are used on flat and low-slope roofs with parapet walls on commercial, industrial, and multifamily residential buildings, as well as on some contemporary single-family homes with parapet-enclosed roof decks. They are also used on balconies and podium decks bounded by walls or guardrails that prevent perimeter drainage.

How to Identify One

Look for rectangular or round metal-lined openings at roof level through a parapet or curb wall. From the exterior, a scupper appears as a projecting metal sleeve or box on the face of the wall near the roofline. From the roof surface, it is the opening where the roof membrane terminates into the wall at a low point. A conductor head — a box-shaped sheet metal collector on the exterior — connecting to a downspout indicates a scupper above it.

Replacement

Scuppers are replaced when the sleeve corrodes or separates from the wall, when the flashing integration with the roof membrane fails and causes leaks, or when the drainage capacity is inadequate and overflow conditions are too frequent. Replacement involves removing the roofing membrane and flashing at the scupper location, cutting out the old sleeve, fabricating or purchasing a replacement unit, reinstalling and reflashing, and restoring the roof membrane. This work is typically performed by a roofer with sheet metal experience and may require permits.