Ponding water (standing water) is one of the biggest threats to flat and low-slope roof longevity. It stresses seams, increases UV/thermal cycling, and can expose weak details fast.
Why ponding happens
- Drain clogs: leaves, gravel, roofing debris, or roof grit block flow.
- Insufficient slope: low areas that never fully drain.
- Deflection/settling: structural movement or insulation compression creates a “birdbath.”
- Drainage design: too few drains/scuppers for roof area.
Why ponding matters
- Accelerates membrane aging
- Increases leak risk at seams and penetrations
- Raises the chance of interior damage during storms
- Makes maintenance problems (like debris buildup) worse
Fix options (from simplest to most involved)
1) Maintenance + drain service
Sometimes the “pond” is just a clogged drain or scupper. Cleaning and verifying flow is step one.
2) Add or upgrade drainage points
Additional drains or scuppers can reduce water depth and improve performance.
3) Rebuild slope with tapered insulation (during reroof)
If the roof has chronic low spots, tapered insulation creates positive drainage and is one of the most durable long-term fixes.
4) Detail rebuilds at weak points
Even if you don’t rebuild slope immediately, flashing and transition details can be reinforced to reduce leak risk.
What not to do
- Assume coating “fixes” ponding without addressing slope or drainage
- Ignore small ponds that return after every rain
- Rely on patch sealant as a permanent solution
Next step
If you have a low-slope roof, explore flat roofing and compare systems in our TPO vs modified bitumen guide. To document ponding zones and options, request an inspection.