Ponding on flat roofs

Roofing · Modified Bitumen · printed page 24 (PDF page 25)

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Book index entries

Ponding Ponding on Flat Roofs Built-up Roofing

Text in the illustration

any roof that still has water on it after 48 hours is defined as a ponding roof
a dry roof may show signs of ponding - dirty circles on the roof or algae/vegetation growth
ponding water
scupper drain
sagging roof joists can render perimeter drains ineffective by allowing water to pond in the middle of the roof

Generated explanation

An oblique view of a building shows a flat roof enclosed by parapet walls, with a large pool of standing water in the middle. A scupper drain is visible through a parapet, and an exterior collector and downspout are shown on another wall. The annotations explain that sagging roof joists can allow water to collect centrally rather than reach perimeter drains. The illustration defines ponding as water remaining after 48 hours and notes that dirty circles or algae/vegetation growth can indicate ponding on a dry roof.

Components

flat roof roof covering parapet walls scupper drain downspout collector downspout

Defects shown

standing water on a flat roof ineffective perimeter drainage sagging roof joists described as a cause of central ponding dirty circles and algae/vegetation growth described as evidence of ponding