Understanding Your Commercial Roof’s Drainage System

Understanding Your Commercial Roof's Drainage System

Water is the root cause of many of the most common forms of roofing damage, like mold growth, weakened insulation, and rotting internal building structures. Thankfully, your commercial roof comes with an efficient drainage system to direct harmful water to the ground or sewer. Therefore, your drainage system is an integral aspect of your roof’s longevity and the safety of your business.

Make sure to get your drainage system cleaned and maintained a minimum of twice a year, preferably once every three months. It’s easy to tackle the regular cleanings on your own, as long as you know where to look. The four main types of drains are scuppers, gutters, downspouts, and internal drains. This guide will help you recognize your drains and understand how they keep your roof functioning optimally.


A roof scupper is a type of edge drain, in other words, a drain located on the perimeter of the roof. Similar to a bathtub overflow drain, a scupper is essentially an opening in the parapet wall that allows water to flow down the side of the building. Usually recognizable by its square or round shape, it is sometimes accompanied by a downspout or gutter to guide the water directly to the ground. When scuppers are used as a critical component of your roof’s core drainage system, they are placed directly in line with the surface level of the roof. If used only as a backup against severe overflow, they are commonly placed a few inches above the roof surface.

Compared to internal drains, scuppers are cheap and easy to install, considering they don’t require tearing open the roof. As such, they are also easy to maintain, requiring only the occasional check for clogs. Scuppers also tend to be the most aesthetically attractive and often come with a decorative design.


Gutters are another highly affordable and easily maintained type of edge drain. However, they are only effective as long as they remain clear of debris. Though gutters are most commonly used on residential buildings, commercial buildings will also sometimes incorporate them in conjunction with the roof’s slope. It’s best to have gutter installation Chicago install the gutters for you. A professional knows all the needed steps of installation to ensure they work properly.

Gravity pushes water along the slope until it falls off the edge into the gutter, located just below the roof’s perimeter. These metal half pipes travel horizontally along the roof, leading the water straight into a downspout. Consider what type of gutter guards are available to keep debris from filling the gutters and blocking rain from pouring out. Learn more at bristle gutter guard.


Downspouts, or roof drain leaders, are pipes that carry water vertically from the top of the roof down to ground level. Often attached to gutters or scuppers on the building walls, they ensure that as little water as possible runs down the side of the building. Otherwise, water running along the walls could cause structural damage, erosion, plant or fungus growth, or lateral leakage. Just like scuppers and gutters, downspouts are also reasonably cheap and require regular maintenance to keep them unclogged.

Internal Drains

Internal drains are like the drains you see in sinks and showers, acting as the threshold to the building’s internal system of pipes underneath the roof. Ultimately, these pipes connect to the gutters and downspouts, leading water safely to the exterior of the building and the ground. Internal drains sit within the basin of a slight slope, usually in the center of the roof or wherever water is most likely to collect. They are the best type of drain to prevent water from damaging the building’s foundation, as long as the drain bowl, basket, and sump are kept clean. Because these drains lead to the interior of the roofing structure, they may require professional help to clean and maintain.

Sitting water is the number one enemy to your roof’s health. Yet, this tricky opponent won’t hinder your business operations as long as you keep your drains clear. Once you understand each type of drain, you’ll know where to inspect your roof for clogs and other damages to your drainage system.

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