2 Reasons Flat Roofs Leak In Heavy Rain

Your commercial property has what is casually called a flat roof, but it is not really flat. It is “low-slope,” meaning it most likely just barely helps water shed into gutters and scuppers. That ¼:12 slope (two percent) may seem like one reason water leaks in instead of running off, but it is not the main problem. In fact, it is not even one of the two main problems.

Water, Water Everywhere

In Fort Myers we get a bit of rain. Sperling’s Best Places puts annual rainfall at 53 inches, a full 14 inches above the national average. Miami is even more generously blessed with precipitation: 61 inches annually. All that rain has to go somewhere, and it is often driven into weak spots on your roof by the high winds so common to south Florida.

Rooftop internal drains and exterior parapet scuppers can be easily overwhelmed under the twin assault of heavy rain and high winds. Clogged drains allow water to back up onto the roof, compressing the sloping insulation and leading to ponding.

If your roof is neglected, this ponding gets worse with each rainstorm so over time you may even have plants growing in low spots on the roof. The organic debris at internal drains and scuppers can also break down and provide rich soil for more plant life.

Ponding water will seep into any open spot or weak area in your low-slope roof. A steady drip-drip-drip will ruin insulation, weaken the roof deck, and lead to increased humidity inside your building.

No Place To Hide

Your low-slope roof is not a barren landscape. It is pierced by sanitary stacks, HVAC equipment, ventilation ducts, and other openings. Rain gets driven into every nook and cranny on your commercial roof, including all those penetrations.

Though the roof area around a vent may be watertight, the wind can carry water into the vent itself. With a long, steady storm or a hurricane, this can mean gallons of water entering your structure.


Systematic and thorough roof inspection, coupled with regular roof maintenance, can lessen the impact of wind-blown rains and hurricanes. Enlist your local, reliable roofer for help preventing water leaks on your low-slope roof.

PSI Roofing knows low-slope roofs. We have the expertise, the experience, and the right equipment to deal with your roof’s leaks. Please contact PSI Roofing today so your commercial property can stay drier tomorrow.