Best Drainage Solutions For a Flat Roof

Not many consider exactly how different the drain system operates in their home or building. Many typically have no idea how water and waste are drained out and disposed of. They do not consider nor explore any other form of drainage system other than the system that they have. And to their credit, many do not have the time to organize how each drainage system works and the good and bad points of each. Doing the research on these types of things can take a long time, and require a lot of attention, causing you to get overwhelmed. Listed below are drainage solutions for a flat roof, their good qualities, as well as their bad qualities.

Keep in mind that these are solutions for a flat roof. If the building or home you own does not have a flat roof, you can stop reading now unless you are considering owning a place with a flat roof in the future. This is because different roofs have different drainage systems and solutions. In particular, a flat roof has no slant, meaning that it cannot drain automatically. While this can also be an issue in slanted or sloped roofs, it usually is not. However, if a drainage solution below can also work for a building that with a slanted roof or can make drainage more efficient for a sloped or slanted roof, it will be mentioned.

Another thing to keep in mind is that although this is a list of drainage solutions, they are not the only drainage solutions available. Other drainage solutions likely exist outside of this, and they should certainly be explored. If you are interested in finding out the best drainage solution for your roof, get in touch with a trusted roofing contractor near you!

What is a Flat Roof Drainage System?

Before beginning the list, it is important to describe exactly what demands a flat roof drainage system. This information is important as it will describe many common characteristics of each drainage solution. All flat roof drainage systems possess a network of pipes and other plumbing, and they all should be able to flush out more than just water. Also, if a flat roof building does not have a properly maintained drainage system, the results can be pretty unsavory: water damage and leaks are still possible even if you have a very ideal drainage system.

3 Most Common Flat Roof Drainage Systems

There are three common flat roof drainage systems. They all accomplish generally the same thing; draining water and other materials out of the roof and away from it. However, they are all different in terms of size, cost, and design. Keep these in mind when choosing one.

Interior Drains

Description: An interior drain essentially turns your flat roof into a sink. A drain is installed in the roof, which is then followed by a network of pipes that transport the water and other debris outside of the building. Most interior drains are placed at the center of a flat roof. The network of piping and plumbing is inside the building, which makes interior drains the only drainage solution that is not visible outside.

Pros: The piping networks of an interior drain are protected from anything that happens outside of the building. It also “focuses” water (and other debris) to the center of the roof, reducing damage to the walls of the building.

Cons: Because of the fact that this drainage system involves opening up a separate drain line in your building, interior drains are the most expensive of the three drainage solutions. Also, even if you have a strainer to catch debris, it still must be cleaned out regularly.


Description: If you have ever seen a pipe at the end of a flat roof that water is shooting out of, this is a scupper. Installed on the edges of a flat roof, it shoots out water and other debris, usually onto a separate gutter or some other slanted surface which then gets funneled to reach the ground, this way water is not falling directly from the building onto anybody.

Pros: Scuppers are cheap to install and are the most efficient way of protecting a flat roof from debris. This is especially true if they are really big. The leaves and other debris that a strainer in an interior drainage system blocks (which also slows down water flow, causing leaks) are never an issue if scuppers are built, especially if the scupper is big enough to pass leaves through.

Cons: Ice and snow will render scuppers useless. This is because snow and ice can block passage to the scupper, resulting in massive leaks when the snow and ice melt. Also, ideally, scuppers should be coupled with another slope like structure, this way water and other debris do not fall directly off of the side of the building.


Description: Gutters are in virtually every building, even in buildings with a slanted roof. They will catch any and all forms of debris. They usually flow into pipes which then transport water and debris onto the ground. Of these three solutions, gutters are far and wide the most common.

Pros: Gutters are the cheapest drainage solution money can buy. They are also easy to install, and it is possible to install them yourself with the right materials. Different than interior drains, they can handle any form of debris.

Cons: Because they can handle any form of debris, gutters must be cleaned out–constantly. If you have made the decision to install gutters and have not made the commitment to cleaning them at least once per month, then you will not have an effective drainage system. Gutters can fill with debris (like leaves, or even dead birds and pests) quickly. And when this happens, they will overflow then water will begin spilling outside the edge of the building. It will cause massive leaks as well. If you do not clean your gutters at least once a month, you should expect major leaks.

As mentioned previously, these are not the only three drainage systems in existence. There are more out there, and it is not necessary to only choose from these three. However, these three should give you a decent start in your search for an efficient drainage system for your building or home.


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