Roof valley replacement
In short
Replacing a valley means taking the slates or tiles off either side to get at the lining, then relining it properly — correct code lead in appropriate lengths on a sound valley board, or a modern liner where the geometry suits. Sizing it for what actually drains into it is the part that gets missed.
Also called: New lead valley · Valley lining · Replace roof valley · GRP valley
Signs you need this
- Splits or holes in the existing valley lining
- Damp on a ceiling below where two roof slopes meet
- A valley that leaks only in heavy rain
- Cement or mortar 'repairs' along the valley sides
- Bituminous paint or tape over the lining
- An extension whose roof discharges into an original valley
A valley carries the water off two roof slopes at once, which makes it the busiest part of any roof and the one where failure does the most damage fastest. Replacing one is a bigger job than it sounds, because the lining sits under the covering — so the slates or tiles either side have to come off to reach it.
The commonest reason for replacement is lead that has fatigued. Lead moves a great deal with temperature, and a valley laid as one continuous strip from ridge to eaves will work-harden and split, always across the middle, usually within ten to fifteen years. Correct practice is lengths with proper laps and a suitable fall, so each piece can move without stressing.
Code matters too. Valleys take real volume and real velocity, so they want heavier lead than a simple flashing — code 5 or above rather than code 4 — and they want a smooth, sound valley board underneath with no sharp arris to cut into the sheet. Lead dressed over a rough or splintered board thins at that point and fails there.
Capacity is the thing most often overlooked at replacement, and it is the reason some valleys leak only in heavy rain. A valley sized for the roof as originally built can be genuinely inadequate once a rear extension has been added and its slope discharges into the same channel. Replacing like-for-like in that situation puts the same failure back — the correct answer is a wider valley, or splitting the discharge.
Modern alternatives are legitimate and sometimes better. GRP and fibre-reinforced valley liners come in long lengths with no thermal movement problem, they suit awkward geometry, and they remove the lead theft risk that has become a real issue on some buildings. On a period or conservation-area property lead is usually still the right answer visually as well as technically.
Whatever the lining, the detailing either side decides whether it works. The covering has to be cut cleanly to a consistent margin, the tilt fillet has to lift the edge of the slate or tile so water cannot track sideways under it, and the bottom end has to discharge into the gutter rather than behind it. A new valley with a poor margin and no tilt fillet will leak in driven rain despite the lining being perfect.
What the job covers
- Covering lifted either side to expose the full lining
- Valley boards checked and renewed where rotten
- Correct code lead in properly lapped lengths, or a modern liner
- Valley sized against what actually drains into it
- Tilt fillets fitted and the covering cut to a clean margin
- Bottom end detailed to discharge into the gutter
What it costs
We don't publish a price for this yet, because a number pulled out of the air is worse than no number at all — your roofer has to honour it. On roofing it would also be close to meaningless: access is often the biggest single factor, and it varies enormously house to house. You'll get a firm price for your actual job when they ring you back, before any work starts. The quote itself is free and there's no obligation either way.
Common questions
Why did my last valley only last fifteen years?
Almost certainly because it was laid as one continuous length. Lead moves substantially with temperature, and a long restrained piece work-hardens and splits across the middle. Correct practice is shorter lapped lengths, which is slower to lay and lasts several times longer.
Do the slates either side have to come off?
Yes — the lining sits under the covering, so there is no way to replace it without lifting the slates or tiles along both sides. That is why a valley replacement costs considerably more than a flashing repair, and why it is worth doing properly once rather than patching repeatedly.
Is lead still the best material?
For a traditional roof, generally yes, provided it is correctly sized and laid in appropriate lengths. GRP and fibre liners are legitimate alternatives that suit awkward geometry and remove any lead theft risk. On a period or conservation-area building, lead is usually right visually as well as technically.
My valley overflows in heavy rain. Will a new one fix it?
Only if it is sized for what now drains into it. A like-for-like replacement of an undersized valley puts the same problem back. If an extension has been added since the roof was built, the catchment may have grown well beyond what the original channel was designed for, and the new valley needs to be wider.
Need this doing in Macclesfield?
Tell us the job and it goes straight to our local roofer — one call back, usually the same day. Free quote, no obligation.