Ponding water is water that stays on a flat roof for more than about 48 hours after rain. On Phoenix flat roofs it usually follows monsoon downpours, and it’s one of the main reasons flat roofs wear out early. Ponding speeds up coating breakdown, adds weight, and eventually finds its way through any small crack. Perfect Roofing corrects drainage and restores flat roofs through our flat roofing service.
What causes ponding water on a flat roof?
- Clogged drains and scuppers blocked by leaves, dust and debris.
- Low spots from deck deflection or settling over time.
- Insufficient slope in the original roof design.
- Rooftop equipment like AC units that block water flow.
- Built-up roofing layers that change how the surface drains.
Why is ponding water a problem?
- Faster coating wear: standing water and sun together break down coatings sooner, especially acrylics.
- Leaks: water held against seams, flashing and small cracks eventually gets through.
- Added weight: standing water stresses the deck in low spots, which can deepen the low spot.
- Debris and growth: dirt and organic material collect where water sits.
If ponding has already caused a leak, our guide to the signs of a roof leak explains how to spot related damage inside.
How is ponding water fixed?
Clear and improve drainage
Drains and scuppers are cleared, and additional scuppers or drains are added where water has no path off the roof.
Build slope with tapered foam or crickets
Spray foam can be applied in varying thickness to build slope toward drains. Crickets (small sloped ridges) redirect water around obstacles like AC curbs and chimneys.
Restore and recoat
Once drainage is corrected, the roof is repaired and recoated. Silicone coatings resist occasional standing water better than acrylics. Our foam roof recoating guide compares coatings and timing.
Replace if saturated
If water has soaked into the roof layers or insulation, those areas need removal before the roof is rebuilt with proper slope.
Prevent ponding before monsoon season
Have drains and scuppers cleared and the roof inspected each spring before monsoon season starts on June 15. A roof inspection finds low spots and worn coating before the storms arrive.
Frequently asked questions
How long can water sit on a flat roof?
Water that remains on a flat roof more than about 48 hours after rain is generally considered ponding and should be corrected.
Is ponding water covered by roof warranties?
Many roofing manufacturers exclude damage caused by ponding water. Correcting drainage protects both the roof and its warranty.
Can you fix ponding without replacing the roof?
Often, yes. Clearing drains, adding scuppers, and building up low spots with tapered foam or other slope corrections can fix ponding on a sound roof.
