Definition of Roof Scupper

A roof scupper is an opening in a roof deck or parapet that allows water to drain off. Scuppers are an important part of any roof drainage system. They serve as overflow drainage outlets when the primary roof drains become clogged or overwhelmed by heavy rainfall. Understanding what roof scuppers are and how they work is key for proper roof maintenance and preventing water damage.

What Exactly is a Roof Scupper?

A roof scupper, also referred to as a parapet scupper or wall scupper, is a vertical opening that allows water to drain off a roof. Scuppers are usually installed at perimeter edges and parapet walls where pooling water has no other escape point.

Scuppers are typically rectangular openings with a sleeve or pipe that penetrates the roof deck. The sleeves extend vertically through the roof line and out the side of the parapet or building. This allows any accumulated water on the roof to exit the roofline and drain away from the building’s foundation.

Key Features of Roof Scuppers:

  • Rectangular or square openings cut into the roof deck or parapet wall
  • A sleeve or pipe extending vertically from the roof deck out past the exterior wall
  • Overflow drainage outlets used in addition to primary roof drains
  • Critical safety feature to prevent ponding water from exceeding roof load capacity
  • Allows water drainage even when primary drains are clogged or overflowing

Scuppers are a fail-safe system designed to prevent the potentially catastrophic pooling of water on a roof. They serve as secondary or emergency overflow drains when the main drainage system cannot handle the volume of water.

Where Are Roof Scuppers Installed?

Roof scuppers are installed in key locations where water is likely to accumulate and pool if the primary drains become overwhelmed.

The most common locations for scuppers include:

  • Perimeter edges – Scuppers are often placed about every 10 feet along the perimeter edges of a flat or low-sloped roof. This prevents ponding at the roof edges if the interior drains cannot keep up.
  • Parapet walls – Scuppers are installed at regular intervals along parapet walls or raised edges. This allows water to overflow before it accumulates too high and adds stress to the walls.
  • Large roof sections – Larger flat roof sections may require several scuppers spread out to facilitate drainage and prevent the entire area from pooling water.
  • Corners – The corners of angled parapet walls or building intersections often house scuppers to allow for drainage at these dead ends.

Proper scupper placement depends on the roof’s size, slope, drainage, and parapet design. A qualified roofing professional can help determine optimal scupper locations. But in general, installation at any dead end or low point vulnerable to water accumulation is key.

How Do Roof Scuppers Work?

Roof scuppers provide secondary drainage on a roof by allowing water to exit or overflow at the roof line. Here is how they work:

  • Rainwater lands on the roof surface and drains towards the interior roof drains. These primary drains remove water and discharge it safely away from the foundation.
  • During periods of heavy rainfall, the interior roof drains can reach capacity and become overwhelmed. If the drains cannot keep up, water starts to pond in low areas.
  • Once ponded water reaches the height of the scuppers, it will begin flowing sideways along the roof, entering the scupper openings.
  • Scuppers have interior sleeves or pipes that allow the water to run vertically through the roof deck and parapet. The water exits past the exterior of the roof line.
  • Uncontrolled water spills out the exterior side of the scuppers, safely diverting it away from the saturated roof drains.
  • Scuppers serve as overflow valves, preventing the roof from exceeding its load capacity due to ponding water. Once rainfall subsides, normal drainage ensues.

The secondary roof drainage capacity scuppers provide is extremely important for building safety. The next section covers this in more detail.

Why Are Roof Scuppers Important for Safety?

Roof scuppers play an integral role in safety by preventing the buildup of excess water weight. Here are some key reasons scuppers are vital to roof well-being:

  • Prevent Water Ponding – Scuppers allow ponded water to escape off the roof. This prevents excess pooling which can collapse a roof deck.
  • Control Roof Weight Loads – Water weighs over 5 lbs per square foot. Scuppers divert water off the roof before live loads exceed safety margins.
  • Prevent Leaks & Water Damage – Scuppers drain water safely off the roof instead of letting it back up under membranes or leak through the structure.
  • Improve Roof Drainage – Scuppers supplement interior drains and gutter systems by multiplying drainage outlets.
  • Serve as Emergency Overflow – Scuppers are a fail-safe overflow outlet if primary drains clog or cannot handle heavy rain loads.
  • Comply with Codes – Building codes require controlled roof drainage. Scuppers are mandatory in many jurisdictions for low-slope commercial roofs.

In short, scuppers are an indispensable tool for safe roof water management. They work hand in hand with interior roof drains to prevent hazardous conditions like uncontrolled ponding.

Roof Scupper Construction and Materials

Roof scuppers consist of a cut opening and a sleeve penetrating the roof deck. The scupper assembly must be watertight and durable to handle overflow drainage.

Scupper Opening

The scupper opening is a rectangular hole cut into the roof deck or parapet. The size is proportional to the required drainage capacity based on factors like roof slope and area.

Typical scupper openings range from 4”x6” up to 12”x12” or more. On low slope roofs, the longest side is oriented parallel with the roof deck for maximum drainage.

Sheet metal is used to line the scupper opening. This metal flange is integrated with the roofing membrane for a reliable seal. The flange may be level with the roof surface or rise up to an inch above it to prevent debris accumulation.

Scupper Sleeve

The scupper sleeve extends from the roof deck down through the roof and parapet to divert water outside the roof line. This component is typically made from leakproof galvanized steel or another metal pipe.

The sleeve extends a sufficient distance past the exterior wall to prevent water from dripping back onto the facade. A decorative metal hood can be added to the exterior portion.

The critical sleeve-to-deck connection point must be completely watertight. This juncture is sealed with a rubber gasket, lead flashing, or liquid sealant compatible with the roof membrane.

Sleeves are securely installed prior to the roofing for proper weatherproofing. Coordinate roof and wall membranes so water is fully directed away from the building.

Roof Scupper Sizes: Calculations and Code Requirements

Roof scupper sizing and placement must follow certain calculations and building codes. Improperly sized scuppers can lead to hazardous roof ponding and drainage issues.

Scupper Drainage Capacity

The required scupper drainage capacity depends on factors like the roof area, slope, and rainfall intensity. Building codes provide minimum scupper sizes for typical roof conditions.

As a general rule of thumb, scuppers should be capable of handling around 4 gallons per minute per 10 square feet of roof area. Specific calculations help refine the ideal drainage rate.

Building Code Requirements

Most U.S. jurisdictions follow International Building Code standards for roof drainage and scupper installation. Key requirements include:

  • Low slope roofs under 2:12 pitch require overflow scuppers at parapet walls and perimeters
  • Scuppers must be spaced no further than 10 feet apart
  • The roof must be able to drain within 24 hours after rainfall
  • Scuppers are sized to the 100-year hourly rainfall rate for the location
  • Minimum scupper dimensions are 4” x 2” with the long side on the roof surface

Always verify your local building codes for applicable roof drainage laws. A licensed roofing contractor can ensure your scuppers meet all requirements.

Roof Scupper Maintenance

Like any roof feature, scuppers require periodic inspection and maintenance to remain functional. Monitor scuppers for any needed repairs or improvements over time.

Signs of Roof Scupper Problems:

  • Obstructions and debris around the outlet
  • Leaks at seams or connections
  • Corrosion and rust on the scupper sleeve
  • Cracks, holes, or damage to the opening
  • Water ponding at the scupper location
  • Water overflowing at non-scupper areas

Scupper Maintenance Tips:

  • Clear any accumulated debris around scupper openings
  • Patch any leaky connections with compatible sealant
  • Replace old and corroded scupper sleeves
  • Repair cracked or damaged portions of the roof opening
  • Consider adding additional scuppers if ponding persists in areas
  • Check overall roof drainage capacity for any needed upgrades

With periodic inspection and maintenance, roof scuppers can effectively serve as critical secondary drainage outlets for years. Contact a professional roofer if you have any concerns about your building’s scuppers.

Roof Scupper Frequently Asked Questions

What is the difference between a roof scupper and roof drain?

Roof drains are the primary interior drainage system installed at low points on flat roofs. Scuppers are secondary exterior overflow outlets placed at perimeter edges and parapets as an emergency drainage backup.

Where should roof scuppers be located?

Typical scupper locations include roof perimeter edges, parapet walls, large open roof areas, and roof corners or sections with no interior drains. They should be installed wherever ponding is likely.

How many roof scuppers are needed?

As a general rule, scuppers should be spaced no more than 10 feet apart along required edges, with the capacity to drain around 4 gallons per minute per 10 square feet of roof space.

What is the best material for a roof scupper?

Galvanized steel is commonly used for scupper sleeves. The roof opening is lined with sheet metal and includes a rubber gasket for waterproofing the seam. Durable, leakproof materials are essential.

Can roof scuppers be blocked or covered?

It is hazardous to block roof scuppers in any way. They must remain open and free of debris to function as emergency drainage outlets when needed. Never cover scuppers.

How often should roof scuppers be inspected?

Roof scuppers should be visually inspected twice per year, ideally in spring and fall. Check for any damage, leaks, or obstructions and clear any debris or buildup around the outlets.

Do all flat roofs require overflow scuppers?

Most commercial low-slope roofs below 2:12 pitch require secondary roof scupper drainage according to International Building Code regulations. Always check your local codes.

What causes roof scuppers to leak?

Age, damage, and improper installation can cause scupper sleeves to detach from the roof deck, leading to leaks. Make sure scuppers are well-sealed at all seams and connection points.

How do you clean clogged roof scuppers?

Use a wire brush, hose, and vacuum to gently clear any accumulated leaves, debris, dirt, or buildup from inside and around roof scupper drain openings. Avoid damaging components.

Can roof scuppers be added after a roof is already in place?

It is possible to retroactively install scuppers, but it is better to integrate them during roof construction for proper weatherproofing. Consult a roofer on adding to an existing roof.

Key Takeaways on Roof Scuppers

  • Roof scuppers are vertical slit openings used as secondary drainage outlets on flat or low-pitched roofs.
  • They serve as emergency overflow drainage located at parapet walls, perimeter edges, and other areas prone to water ponding.
  • Scuppers penetrate the roof deck and divert water safely off the roof when interior roof drains are overwhelmed.
  • Proper sizing and placement of scuppers is critical for controlling roof water loads and preventing structural issues.
  • Scuppers should be regularly inspected and cleaned out to maintain optimal roof drainage capacity.
  • Contact a professional roofer if your building requires scupper installation, repairs, or maintenance for full roof water management protection.

This comprehensive guide covers everything you need to know about roof scuppers and their importance for proper roof drainage and safety. With key information on sizing, installation, materials, building codes, and tips for inspection and maintenance, you can better understand how these critical roof structures keep buildings safely conditioned when facing heavy rainfall.