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How Do Flat Roofs Drain?

Published on Friday October 21, 2022

flat roof

Flat roofs can transform any home by providing an opportunity for a gorgeous rooftop garden or a stylish, weather-resistant outdoor living area — but what happens when it rains or snows? How do flat roofs drain?

It’s important to know how flat roofs drain so you know how to best maintain them. There are three basic flat roof drain systems: gutters, interior drains, and scuppers. Read on to learn more about how these draining systems work.

What is a Flat Roof?

A flat roof is exactly what it sounds like: a roof that is flat without any angles or pitches. It’s common for commercial buildings to have a flat roof thanks to their easy, low-cost installation. They’re also commonly seen in older homes. 

There are several types of flat roof systems available to homeowners, such as built-up roofing, rubber roofs, and modified bitumen systems. Many flat roofs are installed on a slope to allow rainwater to flow off the roof. Some others are installed with a unique flat roof drain system to handle precipitation. 

Pros and Cons of a Flat Roof Drain System

Pro: Affordable Installation

Due to the few materials required and a straightforward design, flat roofs are a reasonably affordable roof installation. This roof style can be installed quickly, cheaply, and with less effort compared to other roofing types. 

Pro: Minimalist Design

A flat roof can be the ideal option for you if you value a simple, minimalist style of home. They offer a very simple style that can look quite nice on a suitable house or commercial structure.

Con: Brief Lifespan 

Flat roofs often have a shorter lifespan than other types of roofs since they have a flat surface and less slope means less opportunity for water to run off. They may only last for 10 years before serious repairs or a replacement is necessary.

Con: Increased Chance of Roof Leaks

A flat roof’s design means that it isn’t the best roof type to drain water completely. Rain, snow, and ice have a propensity to settle a little bit more securely on a flat roof than other roof types, leading to puddles, damage, and even roof leaks.

How Do Flat Roofs Drain?

All flat roofs that are properly installed should have a flat roof drain system. Here are the most common drainage systems for modern flat roofs:

1. Gutters

Like pitched roofs, flat roofs can have a gutter system. Gutters are the drainage system that is most frequently used for flat roofs. They collect rainfall and direct it into a downspout, which then transports it away from the foundation of the building, much like the gutters installed on sloped roofs. 

Pros of Gutters on Flat Roofs

  • Low installation expense.
  • Easiest flat roof drain system to install.
  • Removes water from the foundation of the home, protecting the walls, doorways, windows, and foundation in situations of heavy precipitation.
  • Reduces water damage to roof and foundation.

Cons of Gutters on Flat Roofs

  • When poorly maintained, they can pull away from the fascia boards and cause damage.
  • They are susceptible to damage from severe weather and clogged debris.
  • Can lead to roof rot when not maintained.

2. Interior Drains

Interior drains are a common flat roof drain system for large buildings. They are also installed in some residential homes. Just like the drain in your sink or shower drains water out and away from your home, interior roof drains work with an interior system of pipes to carry water off the roof and away from the home. These pipes can be found below the surface of the roof and the drains are typically placed at the center.

Pros of Interior Drains for Flat Roofs

  • The drainage system is protected from severe weather.
  • The drainage system carries water away from your home’s foundation and walls.
  • No gutters can boost your home’s curb appeal, especially when using custom fittings.

Cons of Interior Drains for Flat Roofs

  • This is the most expensive flat roof drain system to install.
  • Repairs and maintenance are expensive.
  • Debris can easily clog your system, so this drainage system requires regular attention and routine cleaning or you risk having standing water on your roof’s surface.

3. Scuppers

“Scupper” is a term to describe large, square openings in the outermost wall or curb along a roofline. They can be seen on the outside walls and allow water to pour out the building’s side through these apertures. Scuppers frequently have downspouts constructed just below the apertures to collect water and direct it away from the building.

Pros of Scuppers for Flat Roofs:

  • Highly efficient drainage system.
  • Cost-effective drainage system with easy maintenance.
  • Rarely clogs when they are the correct size.

Cons of Scuppers for Flat Roofs

  • Downspouts must be checked regularly for clogs.
  • Scuppers are not as effective in heavy storms or snowmelt.

Ready for an Upgrade?

Long Roofing is a trusted name in home improvement. With over 7 decades of experience, you can rest assured that your roof replacement is in good hands.

If you have questions about the best flat roof drain system for you, don’t hesitate to reach out to our team of skilled professionals. 

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**Excludes labor. Subject to credit approval.

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