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Gutters, scuppers and conductor heads · Lesson 1 of 4

Gutters, scuppers and conductor heads: principles and terminology

The parts of a roof drainage system and what each does, primary and overflow scuppers, who sizes what, and the hazards in the shop and at the roof edge.

You will be able to: Trace the path of roof water through gutters, scuppers, conductor heads and downspouts, name each part, tell primary from overflow scuppers, and state who sizes the system and the safety boundaries.

12 min · 10 slides · 11 questions

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Slide 1 of 10

The path water takes

Roof water leaves a building one of two ways: into a gutter at an eave, or out through a scupper in a parapet. From there a conductor head and a downspout carry it down.

The CDA describes scuppers as outlets through parapet walls or gravel stops.

A roof drainage system, part by partSection through a low-slope roof. On the left a primary scupper passes through the parapet with its sill at the roof surface; its roof-side flange lies on the roof and is covered by flashing, and it empties into a wider conductor head and downspout. A higher overflow scupper, located elsewhere along the parapet, spills straight out clear of the wall. On the right a box gutter hangs on the eave by a strap, its back below the roof edge; edge metal on the roof turns down the eave and its drip laps into the gutter. An outlet and strainer lead into a downspout. Arrows show the water.ABCCDEFGHJKRoof section, not to scaleDashed: located elsewhere on the parapet

Section through a low-slope roof. On the left a primary scupper passes through the parapet with its sill at the roof surface; its roof-side flange lies on the roof under flashing, and it empties into a wider conductor head and downspout. Above it, a higher overflow scupper spills straight out clear of the wall. On the right a box gutter hangs on the eave by a strap with its back below the roof edge, and edge metal on the roof turns down the eave with its drip lapped into the gutter; an outlet and strainer lead into a downspout. Blue arrows show the water.

A
Primary scupper through the parapet, sill at the roof surface
B
Conductor head: at least 2 in wider than the scupper (CDA, UFGS)
C
Downspout (leader)
D
Overflow scupper: set higher than A, discharging free, no head
E
Hung box gutter at the eave, back below the roof edge, front lower than the back
F
Outlet with wire ball strainer
G
Strap supporting the gutter
H
Edge metal: flange on the roof, drip lapped into the gutter
J
Flashing over the scupper's roof-side flange (CDA)
K
Roof membrane
Section, not to scale. The primary scupper sill sits at the roof surface, its flange extending onto the roof (CDA). The gutter sits below the slope line of the roof (UFGS), with the edge metal lapped into it. The overflow scupper is set higher than the primary and needs no conductor head or downspout (CDA).

Sources

Videos for this lesson

What this video shows: Two general contractors install a built-in gutter recessed into a roof that drains about 1,800 sq ft; shown for the built-in gutter idea only.

Video: Installing a Built-In Gutter | This Old House by This Old House, on YouTube. Chosen from the video's published description.

Glossary

Scupper
An outlet through a parapet wall or gravel stop that lets water off a roof.
Overflow scupper
A scupper set higher than the primary scuppers, so it runs only when they block or are overwhelmed.
Conductor head
A box at the top of a downspout that collects a scupper's water.
Downspout (conductor, leader)
The vertical pipe that carries water down from a scupper, conductor head or gutter; NRCA also calls it a conductor or leader.
Built-in gutter
A sheet-metal gutter lining built into a supporting structure, most often wood framed.
Strap and bracket
In SPRI GT-1 terms, gutter supports from above (strap) and from underneath (bracket).