Few things are as important for protecting a commercial building than proper roof drainage. Flat and low-slope roofs have a different design, meaning that certain systems are better than others. Unlike sloped roofing, flat roofs don’t shed water easily. Therefore, if your building doesn’t have an effective flat roof drainage system, rainwater can pool, degrade materials, and ultimately cause expensive leaks or structural problems. As a commercial roofing contractor, the team at RGB Construction understands the need for adequate drainage and can also make recommendations. In this article, we explore the best flat roof drainage systems available today and the best practices to ensure long-term performance.
Key Takeaways
- Flat and low-slope roofs require effective drainage systems to prevent ponding water, leaks, structural stress, and mold.
- Common commercial flat roof drainage systems include interior drains, scuppers, gutters with downspouts, and tapered insulation for added slope.
- Each system has specific advantages, but all require regular maintenance to remain effective, especially after storms.
- Common issues like blocked drains, improper slope, and gutter damage can be avoided with twice-yearly inspections and prompt cleanings.
Why Does Flat Roof Drainage Matter?
Flat roofs are commonly used in commercial construction, as they add more space efficiency and can be used for HVAC systems. However, the flat or low-slope design brings added challenges. Without proper flat roof drainage systems, the following may happen:
- Ponding water weakening roof membranes and insulation
- Leaks occurring around HVAC units, drains, and seams
- Added weight from water buildup that stresses the roof structure
- Mold and rot developing in damp areas
That’s why choosing the right flat roof drainage system, and maintaining it, is critical for protecting your investment.
Types of Flat Roof Drainage Systems
There are several types of drainage systems used for flat and low-slope commercial roofs. Each offers different advantages depending on the building layout and rainfall exposure. Let’s take a look at the best flat roof drainage systems.
1. Interior Drains
As the name suggests, interior drains are installed at low points in the roof and connected to a network of internal piping that carries water away from the building. Interior drains are ideal for large commercial roofs with minimal slope. Due to the design, interior drains are generally protected from freezing temperatures. Concealed plumbing also maintains your exterior appearance. It’s also effective for large or multi-level buildings.
Maintenance is also straightforward: Install strainers to prevent debris from clogging the drainage system and check them regularly for blockages.
2. Scuppers
Scuppers are openings at the edge of the roof that allow water to drain off into downspouts or diverters. They’re often combined with collector boxes or parapet wall drainage systems.
Scuppers come with the following advantages:
- Easy to maintain and clean
- Lower installation costs than interior drains
- When properly sized, they can handle large volumes of water
3. Gutters and Downspouts
While gutters are more commonly used on residential properties, they can also be used on commercial flat roofs when combined with slight slope toward the edges. Gutters and downspouts are cost-effective. It’s important to keep gutters clear of debris, especially after a storm. Since they’re familiar, most maintenance teams know how to clean them. Gutters can also be customized to fit the size of any roof.
4. Tapered Insulation Systems
While gutters are more commonly used on residential properties, they can also be used on commercial flat roofs when combined with slight slope toward the edges. Consider tapered insulation systems for improving water flow, enhancing insulation performance, and minimizing ponding. If you combine tapered insulation with one of the three flat roof drainage systems mentioned previously, you’ll have more efficient water flow.
What are Common Drainage Problems on Flat Roofs?
Even the best-designed drainage systems can fail without regular care. Here are some of the most common issues we see on commercial flat roofs:
- Blocked drains or scuppers from leaves, gravel, or debris
- Improper slope, leading to water stagnation
- Damaged or detached downspouts
- Collapsed gutters due to ice dams or heavy rain
- Leaks around drain assemblies or seams
Inspections should be done bi-annually or after any major storm to ensure that these problems are caught early. Prevention is better than reacting to a problem that has already become significant and costly.
Maintenance for Flat Roof Drainage Systems
Flat roof drainage systems perform best when they are well-maintained. Here are some recommended maintenance steps to take:
- Inspect drains and gutters twice a year, or more frequently during storm season
- Clear debris after storms, including leaves, twigs, and roofing material
- Flush interior drains to prevent sediment buildup
- Check sealants and flashing around drains for cracks or wear
- Monitor ponding areas to ensure water drains within 48 hours
If your roof consistently shows signs of standing water or leaking, it may be time to upgrade or reconfigure your system.
Schedule an Inspection for Flat Roof Drainage Systems with RGB Construction
Choosing and maintaining flat roof drainage systems is essential to protecting your commercial property from water damage and premature roofing failure. RGB Construction has helped business owners across South Jersey design, install, and maintain high-performance drainage solutions tailored to their unique building needs.
Whether you’re building new, replacing an aging system, or troubleshooting ponding issues, we’re here to help. Call 856-264-9093 or schedule a drainage evaluation online today. Let’s keep your roof—and your investment—dry, safe, and built to last.
