Flat Roof Leaking? Common Causes and What to Do

A flat roof leak won't fix itself, and the longer it's left the more damage it does to insulation, ceilings and timbers below. Here's what's usually behind it, and how to deal with it properly rather than chasing your tail.

Common causes

• Failed seams or laps — especially on older felt roofs where the overlaps have lifted.
• Ponding water sitting on poor falls until it finds a weakness.
• Cracked GRP or perished felt from years of UV and thermal movement.
• Poor detailing around upstands, parapets, outlets and rooflights — the most common leak points of all.
• Blocked outlets and gutters backing water up over upstands.
• Splits from movement in the deck or structure below.

Why guessing is expensive

Water rarely enters where it shows up inside — it tracks along the deck before it drips. So "having a look" and slapping sealant on the nearest suspect spot usually misses the real fault, and the leak comes back. That's why we use electronic leak detection: it pinpoints the exact breach without tearing the roof apart, so the repair is precise and lasting — and it's ideal evidence for insurance or warranty claims.

What to do right now

1. Contain the internal damage — move belongings, catch drips, isolate electrics if water is near fittings.
2. Don't bodge it with the wrong sealant — it can make a proper repair harder.
3. Get the roof assessed quickly before water spreads through insulation and plasterboard.

Repair or replace?

We'll find the source, then tell you honestly whether it's a clean repair or whether the roof is past its life and better off replaced. See also the signs a flat roof needs replacing.

Get expert advice on your roof

JLH are single-ply flat roofing specialists covering Rotherham and across South Yorkshire, backed by a 20-year workmanship warranty. Book a free, no-obligation survey and we'll give you honest advice and a clear, fixed quote.