A downspout on a commercial roof drain directing water away from the building.

Ignoring the health of your commercial roof drains can be disastrous for the overall health of your building and your bottomline. Skipping drain system maintenance can cause you to end up with a flooded roof surface – or worse.

If your roof drainage system needs replacing, it’s important to notice warning signs quickly before backup causes more damage. Here’s all you need to know about commercial roof drains to keep your water flowing and your building in good health.

Why Commercial Roof Drains Are So Important

When your drainage system isn’t working properly, it can lead to ponding on your roof. While you may think that a little bit of water laying on your flat roof isn’t that big of a deal, it can actually lead to a number of issues, including gaps and cracks on the roof itself.

All You Need to Know About Commercial Roof Drainage Solutions

Before we get into the warning signs that a new roof drainage system is on the horizon, let’s give you a crash course on the basics of commercial roof systems so you can identify any specific problem areas.

Types of Commercial Roof Drains

Most commercial buildings have low-sloped or flat roofs. For these kinds of roofs, there are two types of drainage systems – gravity drains and siphonic drains.

Gravity Drain Systems

These drainage systems are usually found on smaller commercial roofs or light commercial operations because larger roofs collect water too quickly for a gravity drain system to function properly. As the name implies, these drains use gravity to move water off the roof. Typically this system is made of four sloped segments that direct the water to a single drain.

Siphonic Systems

Siphonic systems are used for larger commercial buildings. A siphonic system is set up so that a baffle on each drain point keeps air from entering the drain pipe. The pipes have lower atmospheric pressure than the outside area, meaning the water is pulled in faster than just by gravity alone.

This system utilizes straight pipes that connect to a vertical drain pipe entering onto the ground.

Parts That Make Up Commercial Roof Drains

Regardless of what system you have, there are common parts to most commercial roof drains. Below are some of the major components that make up your system.

Interior Drains

Interior drains are set into the roof’s surface. They work best when there is a slight slope in the roof guiding the water to the floor drain. Typically, interior drains have a dome strainer fixed to the pipe with a clamp ring to keep debris out. If you have a siphonic system, there will also be an air baffle.

Edge Drains and Scuppers

Edge drains are placed at the edge of the roof to catch excess water. A scupper is a type of edge drain that is built into the wall or parapet of the roof. Scupper drains need to be checked during the colder months for ice build up, and sometimes, areas of extreme weather need drain covers to protect them.


Gutters are usually found on sloped and residential roofs, but sometimes they’ll be incorporated into a commercial roofing system to help direct water flow.


A downspout is a pipe that works in combination with your scuppers (they’re similar to a gutter). This pipe leads down to the ground and directs water away from your building.


These are entry points that allow you to easily get into the drainage system and remove clogs.

Common Commercial Roof Drain Materials

The parts that make up your system operate differently depending on the kind of material used in its construction. Some are more high-quality than others and will have a longer lifespan.


This is a cost-effective material used in drainage systems. PVC roof drains (aka plastic roof drains) tend to be a little weaker, however, than options like cast iron drains. They do have an advantage in being less-likely to clog, though.


Thermoplastic Polyolefin is similar in many ways to PVC, though it is more fire-resistant. It’s not the best choice for roof drain covers due to how lightweight it is.

Cast Iron

Cast iron roof drains cost a little more, and can clog more often than PVC or TPO. They are extremely durable, however, so they’re often used as drainage covers to keep large debris from entering your drainage system. If heavy debris is an issue for your flat roof, then a cast iron dome strainer will be much more effective than a plastic dome strainer.

Stainless Steel

Stainless steel drainage systems are strong but lightweight, and they can withstand low temperatures without growing brittle.

However, all materials require insulation when being used for exterior pipes in order to survive cold winter temperatures.

Signs You Need New Roof Drains

There are a few telltale signs that you need to replace your roof drains. One we already mentioned – ponding water.

Or course you may not be regularly up on your roof to see if water is pooling there or not – and some water on the roof after a rainstorm may not be a problem. However, if water remains after 48 hours, then you likely have a drainage problem that could affect your roof.

One of the dead giveaways that you have a drainage problem on your hands is the smell. If you start to notice an odor of mildew or stagnant water in the air around your building, call a professional. Water stains around roof vents and stains on your ceiling are two other big warning signs that something is going on with your drainage system. Algae and fungus growing on the roof itself can be a result of poor drainage.

Any visible damage to your downspouts or missing nozzles can also cause drainage issues, and should be checked by a roofing professional.

Don’t Hesitate to Call in the Professionals

If you notice signs that your drainage system is failing – don’t wait to get it checked out. The longer you do, the more damage it causes. It’s best to have any issues checked out by professional roofing experts – like us here at TEMA. We are happy to discuss options for drain replacement and even retrofit roof drain systems.

We understand how urgent a failing commercial roof drain (or entire roofing system) can be, so we offer 24-hour emergency roofing repair services, along with regular maintenance checks and quality customer service. When you hire TEMA, you’re partnering with roofing professionals who care about the health of your commercial roof, and the well-being of your business. Contact us today for a free consultation.