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Engineers design roof drainage systems based on rainfall statistics. The ASCE (American Society of Civil Engineers) and IPC (International Plumbing Code) consider a 100-year rainfall (a rare and intense rainfall event with a 1% probability of occurring in any given year) measured during 15 to 60 minutes.
However, historical data has taught that drainage systems of most membrane roof systems will experience a downpour exceeding the 100-year design rainfall.
The combination of severe rainfall and an inefficient roof drainage system will produce a water depth beyond what the roof can handle, causing immediate structural collapse or mid- to long-term roof deterioration, leaks, and related problems such as algae and moss growth or insect pest infestation—mosquitoes.
Scupper drains are cost-effective roof drainages that prevent structural failure by keeping water from overloading the structure during heavy rainfalls.
However, even if your roof already has scupper drains, consider an inspection to ensure they comply with the latest codes and regulation updates or to discard leaks or any other issue due to improper fabrication or installation.
In this post, we’ll share the basis of scupper drains, their types, design considerations, and maintenance tasks.
At Menzies, we’ve been creating long lasting scupper drains for 46 years. Buy with us and see why we are the preferred brand for engineers, architects, and contractors.
What is a scupper drain?
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Scupper drains are openings that go through parapets or curbs at the edge of a flat roof. They let water flow off the roof and away from the building.
Scupper drains cab the primary drainage system of a flat roof or work along the primary (vertical) drainage system (gravity or siphonic), which drains water into piping running through the interior or exterior of the building before it empties either onto grade or into a storm sewer.
Scupper drains are effective in handling large volumes of water, versatile, budget-friendly, and relatively easy to install. They are also a low-maintenance solution and are less prone to clogging than other systems.
Types of Scupper Drains
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Depending on the type of roof and building, scupper drains vary in shape, configurations, and materials.
Based on the Type of Roof
Depending on the roof edge, you can use thru-wall or channel-type scuppers.
Thru-wall scuppers are square or rectangular closed boxes going through parapets.
Channel-type or open-top scuppers are the go-to solution for flat roofs with short walls (flashing, curb, and cant strip) along their edges.
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Both closed-box and channel scuppers can drain water into extended chutes (sometimes known as roof canales) or spouts, while open-top scuppers can also do so into gutters.
Based on the Type of Building & Environment
Let’s break down the different types of roof scupper drains in the context of their suitable uses.
Copper/Aluminum Box Scuppers.
It’s a box structure drainage solution projecting from the wall.
Due to their durability and low maintenance, they are suitable for residential and commercial buildings with large roofs and robust drainage systems within heavy rainfall areas.
Box scuppers provide an aesthetic appeal as well as functional drainage.
Scupper drains are made of copper and aluminum—non-ferrous metals. When in contact with air and water, copper and aluminum scuppers don’t rust but rather corrode, creating an oxide layer that protects the underlying metal against further corrosion.
The main difference between them is the color of the oxide layer. Copper oxide is green and blue-ish, while aluminum oxide looks like a white-gray powder.
Clamp-tite Aluminum/Copper Box Scuppers.
Ideal for commercial and industrial installations where secure, watertight connections are essential to guarantee reliability.
The clamping mechanism ensures a secure and watertight connection between the scupper drain and the roof or wall membrane.
Based on the Design of the Drainage System
The local rainfall intensity and roof area are the main variables affecting the drainage system and, thus, the size, quantity, and location of scupper drains. Of course, code requirements (that vary from state to state) also come into play.
In addition to their size, quantity, and location within the roof area, roof scuppers’ inlet elevation will also vary depending on whether they are part of the primary or secondary (overflow) drainage system.
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Primary scuppers are at the roof’s lowest points, level with the roof surface. Through-wall roof scuppers have a 90-degree flange to fix them to the roof and parapet.
Secondary or overflow scuppers are slightly higher from the roof level, have a flat inlet flange, and function as a backup when extreme rainfalls overcome the internal roof drainage system (see image above at the beginning of this section).
Decorative Scuppers?
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Roof scupper can be either rectangular or round.
Although both shapes drain water effectively, rectangular scuppers have larger cross-sectional areas, allowing a slightly higher volume of water to pass.
So, choosing between rectangular or round scuppers narrows to the building’s architectural style.
The sleek design of round scuppers makes them excellent choices for large, upscale homes with distinct architectural elements.
Scupper Drains Maintenance
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Regularly check the condition of your scupper drains, especially after intense rainfalls.
Remove leaves, twigs, and other debris blocking the scupper openings. If the scuppers drain into gutters or downspouts, check they are also debris-free to prevent backflow and overflow.
Remove ice buildup around scuppers in colder climates to ensure they remain functional.
Functional tests are a simple and effective way to check the condition of a roof scupper. If you suspect a scupper drain or a piece attached to it is clogged (e.g., the spout), pour water into the roof area leading to the scupper to ensure it drains properly.
Lastly, check and replace any deteriorated sealant to maintain a watertight seal. Butyl sealant prevents water from seeping into the building structure and causing the roof to leak when it rains.
Look for any of these leak signs around or near the scupper:
- Water stains or discoloration on the walls directly below the roof scupper.
- Presence of mold or mildew.
- Peeling or bubbling paint and (wallpaper on interior walls) below the scupper.
- Visible dripping water from the scupper area inside and outside the building.
- Wood rot in the roof structure or the parapet wall near the scupper.
Conclusion
The internal drainage system of roofs isn’t bulletproof. The combination of intense rainfall and clogged or undersized drains (caused by improper installation or noncompliance with code updates) can lead to roof failure due to water ponding.
Roof scuppers effectively drain water, preventing water ponds and, thus, structural failure or deterioration.
Not sure what type of scupper drains you need? Call us at 1-800-665-8840. Our team will gladly answer your questions. You can also check out Menzies’s scuppers page for detailed information about our world-class roofing accessories.
