Updated 9 October 2026 · By Efficient Roofing Ltd
Flat roof drainage is what keeps a flat roof alive. A flat roof is never truly flat: it is laid with a slight fall so water runs to a gutter or outlet. When it does not, water sits, and standing water finds every weakness.
Why water ponds
The deck has sagged between joists, the fall was never right, or the outlet is blocked with moss and leaves. Ponding that is still there 48 hours after rain is a sign the drainage needs attention.
What standing water does
It loads the deck, speeds up wear on the covering and freezes in winter, opening up laps and seams. Most flat roof leaks we see start at a ponding spot or at the edge where water runs off.
Outlets and edges
Clearing a blocked outlet or a gutter is the cheapest fix. Drip trims at the edge should throw water into the gutter, not behind it.
Getting the fall right
When a roof is replaced, firring strips or a tapered deck give it a proper fall. That is the permanent cure for ponding, and it is part of every new flat roof we lay.
When to call us
Ponding that does not clear, damp on the ceiling below, splits or blisters in the felt: ring 0118 230 4968 or send the form for a free look.
Questions
Is a little standing water normal?
A thin film that dries within a day or two is not a worry. Deep pools that stay are.
Can ponding be fixed without a new roof?
Sometimes, by clearing outlets or adding an outlet at the low point. If the deck has sagged, it needs relaying with a proper fall.