Roofing Glossary

Ponding Water

Ponding water is standing water that remains on a roof surface 48 hours or more after rain stops. On sloped shingle roofs it should never happen; on flat and low-slope roofs it is the number one enemy.

Ponding is destructive for compounding reasons: water weighs about 5 pounds per square foot per inch of depth, so ponds stress the structure; standing water accelerates UV and chemical breakdown of roofing membranes; and in winter it becomes ice that pries at seams with freeze-thaw force. The roofing industry's rule of thumb: water should drain or evaporate within 48 hours.

Causes include clogged drains and scuppers, settled or sagging deck areas, crushed insulation, and original design with inadequate slope. Fixes range from clearing drains to adding tapered insulation that re-slopes the roof toward drainage points.

Why It Matters

Chronic ponding voids most flat-roof material warranties and dramatically shortens membrane life. If your flat roof holds birdbaths days after rain, the drainage needs correction — not just patching.

What to Watch For

• Visible standing water days after rain
• Stained rings marking historic pond locations
• Sagging areas or depressions in flat roofs

A Maryland Note

Maryland's heavy downpours overwhelm marginal flat-roof drainage fast. Commercial and porch flat roofs here should be checked for ponding every fall.

Questions about your own roof? Request a free estimate or call Nucci Brothers Roofing at (301) 458-1003.