Drains and Scuppers: How to Stop Ponding and Backup Leaks on your Commercial Roof
- Jamie Aylwin
- Sep 25
- 2 min read
One of the most common issues for flat commercial roofs is ponding water. When water lingers for more than 48 hours, it can weaken insulation, overload the deck, and lead to leaks. A well-designed system of roof drains, scuppers, and overflows keeps water moving off the roof safely — but only if those components are properly maintained.
Interior Drains, Scuppers, and Overflows
Interior roof drains channel water through piping inside the building.
Scuppers are openings at the roof edge that allow water to exit sideways.
Overflow scuppers provide backup relief if drains clog or rainfall exceeds design limits.
Every building needs a combination of these elements sized to its square footage and rainfall exposure.
Common Failure Points
Most ponding problems come from simple issues like clogged strainers, blocked scuppers, or deteriorated seals. Left unchecked, standing water can back up under flashings or freeze into ice dams in winter. Quick checks of drains and scuppers often prevent major roof repair costs.
Sizing and Placement Basics
Drain and scupper placement is critical. Building codes typically require overflow scuppers as a secondary safeguard. Proper sizing ensures drains handle design storms without overwhelming the system. For older buildings, undersized drains are a common cause of chronic ponding.
Maintenance and Seasonal Checks
Schedule roof drain inspections at least twice a year — spring and fall — and after severe storms. Maintenance should include clearing debris, testing water flow, and checking for damaged flashing around penetrations. Adding this step to your roof maintenance checklist keeps systems functioning year-round.
When Ponding Signals Bigger Problems
If ponding persists even after drains and scuppers are clear, the issue may be with the roof deck or insulation. Saturated insulation compresses over time, creating low spots where water collects. In these cases, localized replacement or re-sloping may be needed.
Upgrades That Make A Difference
Simple improvements like adding strainers, sumps, or reinforced walk pads around drain fields can greatly reduce clogging and wear. Facility managers often include these small upgrades as part of scheduled commercial roof repair and maintenance.
Pitfalls to Avoid
Relying only on interior drains without overflow protection.
Skipping seasonal cleanings, which nearly guarantees clogs.
Ignoring chronic ponding, which accelerates membrane failure.
FAQ
What is the difference between a drain and a scupper?
Drains send water through piping inside the building, while scuppers let water flow off the edge. Both are important for redundancy.
How often should roof drains be cleaned?
At least twice a year, plus after major storms. Fall is especially important in New England when leaves and debris accumulate.
Can ponding water void a roof warranty?
Yes. Most warranties require proper drainage and will not cover failures caused by standing water.
Don’t let clogged drains or scuppers cause costly damage. Add a drain and scupper inspection to your next seasonal roof service visit with TheRoofers.com.