When it comes to commercial flat roofs, few issues cause as much long-term damage as ponding water. It might not look like much—just a little standing water after a rainstorm—but over time, poor drainage can compromise your roof system, damage insulation, and even lead to structural collapse.
If you manage a commercial property in Missouri or Illinois, here’s what you need to know about stagnant water—and how to stay ahead of it.
What Causes Ponding Water?
Flat roofs aren’t truly flat—they’re designed to slope slightly so water can move toward drains or gutters. But over time, a variety of issues can cause water to stop flowing and start collecting:
Settling of the building or roof deck
Clogged or undersized drains
Poorly installed rooftop units (like HVAC)
Lack of tapered insulation or slope
Debris buildup blocking water flow
We often see ponding water collect around HVAC systems, where condensation lines drip constantly and shaded areas prevent proper drying.
The Hidden Damage Adds Up
Ponding water may not cause immediate leaks, but the longer it sits, the more damage it does:
Premature membrane failure:
Roofing materials break down faster when constantly wet, especially in areas with UV exposure and extreme temperature swings.Mold and saturated insulation:
Water that infiltrates your roof system can soak the insulation layer, creating a perfect environment for mold—and decreasing your building’s energy efficiency.Structural concerns:
When drains back up and water collects too deeply, weight can add up fast. In several recent cases, we’ve seen roofs collapse because of poor drainage—not roofing material failure.
Warning Signs to Watch For
If you’re managing a commercial building, keep an eye out for these common signs of drainage problems:
Pools of water that linger more than 48 hours after rain
Water stains or bubbling near rooftop units
Soft or spongy areas in the roof membrane
Recurring leaks in the same areas
Overflowing gutters or downspouts during storms
What You Can Do About It
There are practical, proactive steps that building owners and facility managers can take to fix ponding water before it leads to bigger issues:
Clean your drains and gutters at least twice a year.
Blocked drainage is one of the most common—and most preventable—causes of ponding.Add overflow systems or secondary drains.
These provide a safety net when your main drainage system is overwhelmed during storms.Install tapered insulation or crickets.
These solutions help redirect water away from trouble spots like HVAC units or skylights.Schedule regular roof inspections.
A professional inspection can catch drainage issues early and help you plan cost-effective repairs before damage spreads.
Don’t Let Water Sit—Let’s Get It Moving
Flat roofs are built to perform, but they’re not built to be swimming pools. The sooner you identify and correct ponding water, the longer your roof will last—and the more money you’ll save in emergency repairs down the road.
Need help identifying problem areas on your roof?
Jewett Roofing is here to help with inspections, drainage solutions, and proactive maintenance plans across the Greater St. Louis and Greenville regions.
Contact us today to schedule an inspection or get a quote on drainage upgrades.
