Flat Roof Ponding Water: Causes and Fixes

Flat roofs are built to drain. When water stays, it is a sign something needs attention.

What Causes Ponding

Clogged drains, low spots, sagging decks and settled insulation all let water stay on a flat roof. Debris from a storm can block a drain in one night.

Heavy water also adds weight to the structure.

What Ponding Does

Water stresses seams and flashing, grows algae and finds tiny flaws in the membrane. It also speeds up aging of the surface.

Many leaks start at a spot where water sits.

How It Is Fixed

Start by clearing drains and scuppers. Then repair seams and low spots, and consider tapered insulation or a recoat.

If the roof is near the end of its life, replacement may be the better choice.