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How Do Flat Roofs Drain? (& 3 Things You Should Know)

Posted on April 15, 2024

How Do Flat Roofs Drain? (& 3 Things You Should Know)

A common problem on flat roofs is water pooling and insufficient drainage because of the low slope. Property owners often look for different drainage methods for flat roofs to address this before any damage is done. Otherwise, if left unattended, water pooling on flat roofs can create structural issues that will cost you more in the long run. 

If you are thinking of installing a flat roof, you might be wondering, ‘How do flat roofs drain?’ By the end of this blog post, you will have an answer to that question and reliable flat roof drainage solutions to help you seamlessly install a flat roof. Keep on reading until the end for three things you should know. 

The Challenges of Flat Roofs

While flat roofs offer many benefits, they also come with their own set of challenges. One of the biggest concerns is proper drainage – without the right slope and drainage system, water can accumulate on the roof, leading to leaks, mold growth, and potential structural damage. This standing water can also attract insects and other pests. Installing the correct flat roof drainage system and regular maintenance is crucial to ensure the roofing material remains in top condition and doesn’t succumb to deterioration and the elements.

 Flat Roofs

Flat Roof Drainage Options

Now, let’s come to the main question of this blog post: how do flat roofs drain? The following are some flat roof drainage options you can choose for your property. 

These systems are carefully engineered to channel water away from the roof’s surface, preventing potential water damage, mold and algae growth, and structural issues. Without them, flat roofs would hold water and deteriorate quickly. 

1. Internal Drains

One of the most common flat roof drainage methods is the use of internal drains. These drains are strategically placed at the lowest points of the roof, acting as funnels for water to flow towards. 

Once the water collects in these drains, it’s then directed through a network of pipes that run vertically down the building and away from the foundation. 

2. Scuppers

Scrappers are openings or outlets that are cut into the parapet wall and allow water to flow off the roof and into external downspouts or gutters.

Scuppers are often used in conjunction with internal drains, providing an additional line of defense against water accumulation. 

3. Gutters and Downspouts

While not as commonly associated with flat roofs as they are with sloped roofs, gutters and downspouts are a crucial part of flat roof drainage systems.

Gutters and downspouts are generally installed along the roof’s perimeter or at strategic low points, ready to catch any water that runs too close to the edge. Once collected, the water is whisked away through the downspouts and safely deposited away from the building. 

Gutters and Downspouts

4. Tapered Insulation and Sloping Materials

Remember how we mentioned that flat roofs aren’t entirely flat? This is where tapered insulation and specialized sloping materials come into play.

These components are not a type of drainage system but are used to create the desired slope for optimal drainage, ensuring that water flows toward the designated outlets or gutters rather than pooling on the roof.

These popular and recommended drainage systems are widely used in commercial and flat roofs to facilitate drainage while preventing water-related damages. 

3 Things To Know About Flat Roof Drainage Systems

1. Flat Roofs Aren’t As Flat As You Think

Despite their name, flat roofs aren’t actually flat – they’re designed with a slight slope to facilitate water drainage. This subtle slope (generally ranging from 1/4 inch to 1/2 inch per foot) isn’t visible to the naked eye, but it plays a crucial role in preventing water from pooling on the roof’s surface.

Without this slope, flat roofs would collect rainwater and put the entire structure at risk of leaks, mold growth, and extensive damage. 

2. Maintenance Is Key 

Even the most advanced flat roof drainage systems won’t function properly without regular maintenance. Debris, leaves, and other particles can easily clog drains, gutters, and downspouts, leading to water buildup and potential leaks. 

Therefore, it’s crucial to schedule regular inspections and cleanings, especially before and after the rainy season. A professional roofing contractor can identify and address any issues, ensuring that your flat roof drainage system is in the best shape and ready to handle any weather conditions. 

3. The Right Roofing Material Matters

The choice of flat roofing materials plays a significant role in ensuring proper drainage and longevity for flat roofs. Each material has unique properties and advantages, so it’s essential to consult with a professional to determine the best fit for your specific needs and climate conditions. 

Some popular flat roofing materials include:

Built-Up Roof (BUR):  This flat roofing option involves multiple layers of waterproof materials, creating a durable and long-lasting roof.

Modified Bitumen: A flexible and cost-effective option that combines asphalt and reinforcing materials for enhanced weather resistance.

EPDM: A synthetic rubber membrane that is highly durable and resistant to various elements, making it a popular choice for flat roofs.

PVC and TPO Membranes: These single-ply roofing membranes offer excellent resistance to UV rays, chemicals, and environmental pollutants, ensuring a long lifespan for your flat roof.

Closing Thoughts

Flat roofs may seem like simple, level structures, but they have slight slopes that help them drain water. From the carefully engineered slopes and strategically placed drains to the gutters and downspouts, these systems ensure water doesn’t pool on the roof. 

By understanding the importance of proper drainage, slope, maintenance, roofing materials, and insulation, you can keep your flat roof dry and prevent potential water damage. 

Choose Renova Roofing & Construction In Mississippi For Your Roofing Needs

Now that you know how a flat roof drains, you can make an informed decision. But, you may still wonder how to choose the right flat roof drainage system. Choosing the right flat roof drainage system isn’t an easy task; it requires a professional roof inspection to assess the current condition of your roof, the local area climate, and the roofing material you have installed. 
That’s why we always recommend property owners call a professional and reliable roofing contractor. If you want to install a flat roof drainage system in Mississippi, choose Renova Roofing & Construction. Contact us for a complete flat roof inspection. Give us a call today at (601) 647-3433 and consult a roofing professional.