Scupper

A scupper is an opening in a wall or parapet that allows water to escape from a roof, terrace or balcony instead of pooling. On low-slope roofs scuppers are set at roof level in parapets and usually discharge into a conductor head (collector box) and downpipe, or directly over the edge.

Types

• Primary (through-wall) scuppers: the main drainage route on roofs drained to the perimeter.
• Overflow (emergency) scuppers: set higher than the primary drains so that, if drains block, water exits the roof before it builds to a depth that overloads the structure or rises above flashings.

Construction

Scuppers are typically formed as metal boxes or sleeves, made of galvanised or coated steel, stainless steel, copper or aluminium, set through the parapet and flashed into the membrane. Single-ply manufacturers supply prefabricated scupper boots; liquid-applied membranes and PMMA are often used to seal them.

Design considerations

• size and number based on rainfall intensity and roof area under the plumbing code (in the US, the International Plumbing Code) or BS EN 12056-3 in the UK and Europe
• crickets or tapered insulation to direct water to the scupper
• flashing heights that remain above the maximum water level in an overflow event
• avoiding discharge onto walkways or building entrances

Advantages and limitations

Scuppers are simple, easy to inspect and less prone to hidden blockage than internal drains. They are limited to roofs where water can be brought to the perimeter, and in cold climates exterior discharge can freeze.