Common Causes of Roof Leaks
By the Quantock Roofing team · Updated 14 June 2026
Roof leaks nearly always come from a handful of usual suspects. Knowing them helps you understand what your roofer is looking for — and why finding a leak properly takes a methodical look rather than a guess.
The usual suspects
Most leaks trace back to one of these:
- • Slipped, cracked or missing tiles and slates
- • Failed or lifted flashing around chimneys, walls and valleys
- • Cracked or washed-out mortar at ridges and verges
- • Blocked or damaged valley gutters
- • Worn or absent underlay beneath the covering
- • Blocked gutters causing water to back up under the edge
The one that isn't a leak
Condensation in a poorly-ventilated loft can mimic a leak exactly — damp timbers, drips and stains — without any water getting in from outside. It's worth checking for, because fixing the wrong problem wastes money. Good ventilation, not sealant, is usually the answer.
Why the source is hard to find
Water runs along battens and rafters before it drips, so the stain inside is often well away from the entry point outside. That's why we trace a leak methodically — internally and externally — before repairing, rather than patching the nearest likely spot and hoping.
