Roof valleys: the highest-risk detail on a pitched roof
A valley collects the water from two slopes and funnels it into one channel. It is the hardest-working square metre on the roof.
Why valleys fail
Volume plus debris. Leaves and moss collect in the channel, water backs up above the lap line, and it goes sideways under the tiles rather than down the valley.
Open lead valleys
The traditional detail: a lead-lined channel with tiles cut to either side. Long-lasting when the lead is the right code and properly supported, but the lead splits if the sheet lengths are too long.
GRP and preformed valleys
Common on modern roofs. Quick and inexpensive, and fine when correctly supported and lapped. They're less tolerant of poor support underneath than lead.
Mitred and swept valleys
Tiles or slates cut and closed across the valley with soakers beneath. Attractive on plain-tile roofs, skilled work, and unforgiving of shortcuts.
Maintenance
Keeping the valley clear of debris is the single cheapest thing you can do to extend its life, particularly on tree-lined streets.
FAQs
The tiles either side normally have to come back to reach the valley itself, but only a narrow band each side rather than the whole slope.
Correctly sized and supported lead lasts for decades. Early failure is usually down to over-long sheets or inadequate support.
Yes — along with chimneys, they're where most of the leaks we attend originate.
Related reading
More on materials & systems and the jobs that usually come with it.
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- New roof cost: what a re-roof really costs in 2026
- Scaffolding for roof work: when you need it and what it costsCosts & budgeting
Looking for something specific? See our roofing services, cost guides, common roof problems or the areas we cover.
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