Flat Roof Ponding: Causes, Risks and Fixes
Ponding is standing water that doesn’t drain away within 48 hours of rain stopping. A small amount that clears quickly is normal on most flat roofs. Water still sitting after two days points to a falls problem, meaning the drainage gradient built into the roof isn’t moving water toward the outlets the way it should.
The risk isn’t just the water itself. Standing water is heavier than most people expect, adding real structural load if it covers a large area. It also accelerates UV and thermal breakdown of the membrane underneath, since the covering is designed to shed water quickly, not sit submerged for days at a time. Over several seasons, that shortens the roof’s working life significantly.
Causes vary. Sometimes the roof was built with an inadequate falls gradient from the start, common on older extensions from the 1970s and 80s. Other times a blocked outlet is the real culprit, and clearing it solves the problem without touching the membrane at all. Because of that, we always check outlets first before recommending anything more invasive.
Fixes range from cheap to substantial depending on the cause. Clearing a blocked outlet costs very little. Adding tapered insulation to correct a falls problem on an existing roof is a bigger job, but often cheaper than a full recover if the membrane itself is otherwise sound. A full replacement with correct falls built in is the permanent fix when the roof is due for renewal anyway.
If you’ve noticed standing water on a flat roof that isn’t clearing, get it checked before it becomes a bigger job. Our flat roofing team surveys the falls as standard, covering Bo’ness, Linlithgow and the wider Forth Valley. We also cover Falkirk and the surrounding area.
Related guides: Flat roof replacement cost guide. Felt vs EPDM vs GRP compared. Signs of a failing flat roof. Garage roof replacement. Conservatory roof replacement. Gutter cleaning and repair. Moss on Your Roof. Roughcasting and Rendering. Velux and Skylight Leaks. Fascias, Soffits and Guttering Explained.
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