Where two roof slopes meet, they form a valley — and that modest strip of metal or fibreglass handles more water than any other part of your roof. Every drop from both slopes funnels through it. So it’s no mystery that valleys are among the first places roofs fail, and among the most common repairs we do across Bristol.
Why valleys work so hard
A valley concentrates the run-off of two slopes into a channel a few inches wide — in a downpour, that’s a small stream. It also collects everything the slopes shed: leaves, moss, grit from ageing tiles. And on terraces and semis, valleys often sit between properties, quietly shared and quietly ignored by both households until water appears on someone’s landing ceiling.
How they fail
Lead valleys fatigue-crack with decades of thermal movement — usually a split across the fold that’s invisible from the ground. Older mortar-and-tile valleys crack and let water track sideways. Fibreglass valleys (common in re-roofs from recent decades) become brittle and crack at fixing points. And any valley blocks: a moss dam an inch high is enough to push a stream of water sideways under the tiles, producing a “leak” on a roof where nothing is actually broken.
The symptoms indoors
Valley leaks classically show as staining on ceilings or walls near the middle of the house — under the junction line — often only in heavy or wind-driven rain, because light rain stays in the channel. Intermittent leaks that only appear in storms are valleys and flashings until proven otherwise.
What repair involves
A blocked valley just needs careful clearing (and pruning whatever feeds it). A cracked one needs the tiles alongside lifted, the old lining repaired or renewed — we use lead in proper bay lengths, as covered on our leadwork page — and the tiles re-fitted with correct margins. Shared valleys between properties are best assessed from both sides; splitting a repair with the neighbour is common and sensible.
The upgrade moment
If a roof is being re-roofed, the valleys should always be renewed while everything is open — reusing a fifty-year-old valley under new tiles is a false economy nobody should sell you.
Stain on the ceiling that only shows after storms? That’s a valley story we’ve heard many times — get in touch and we’ll trace it properly.