The removal of water from the roof surface is critical to the success of the roof system and warranty compliance. The most common method of water removal is through interior roof drains. However, in roof systems with parapet walls that exceed 3 feet in height another form of water removal can be accomplished with thru-wall scuppers. The scuppers can serve as overflow drainage — where the scupper is elevated above the deck a minimum of 2 inches — or as primary drainage — where the scupper is flush with the deck.

Typical Thru-Wall Scupper

Thru-Wall scupper flashing detail courtesy of American Hydrotech, Inc.

In both cases it is critical that the membrane is properly terminated at the scupper opening and that the flashing is applied over the metal scupper flashing at both the horizontal and vertical transitions.