Technical Elements

Through-wall scupper

The NRCA Roofing Manual: Membrane Roof Systems—2007 was issued this month and contains several new details addressing construction scenarios that were not included in the fifth edition. (For more information about the manual and its changes, see "The new manual," on page 23.)

One new detail is BUR-24S, "Mop- or Cold-applied Base Flashing at Through-wall Scupper." Scuppers provide an outlet for water from a parapet wall and are a source of drainage. They can discharge water into a conductor head and downspout, discharge directly into a gutter or be extended to allow unrestricted discharge of water.

Detail BUR-24S from The NRCA Roofing Manual: Membrane Roof Systems—2007

BUR-24S shows a two-piece scupper constructed with sheet metal. The scupper piece located inside the wall is referred to as a scupper liner, and the other piece is an exterior closure flange installed on the wall's outside face. The top and sides of the closure flange are formed to accept sealant; the bottom flange is locked to the conductor head. The top of the conductor head should be 1 inch below the base of the scupper, and NRCA recommends all scupper joints be soldered or welded. In addition, the scupper assembly should be secured to the wall and deck or optional wood blocking.