The two valleys described plainly
A valley is the V-shaped channel where two roof slopes meet, and it carries all the rain from both. Whatever lines it takes the combined runoff of two slopes, so it is a poor place to cut corners.
A lead valley is made from sheets of lead laid in the V over boards, with the tiles or slates cut and dressed neatly to each side. Lead is soft, so it is shaped to the angle of the roof, and it moves with temperature without splitting if the pieces are kept to sensible lengths.
A GRP valley is a gutter moulded from glass-reinforced plastic (GRP, glass fibre set in resin). It is made in a factory or on site, laid in the same V, and it is smooth and joint-free for much of its length. The tiles or slates sit on either side of it and are trimmed to fit.
On the surface the two look quite different. Lead is dull grey and seen only as a narrow band. GRP is often finished in a grey or black colour and can look more uniform. Neither is hard to live with once the roof is done.
Life, cost and what the published figures say
Published life figures exist for both materials, though not for valleys as a separate detail. For GRP roofing, HomeBuilding gives "25-30 years" and Less gives "25 to 40 years". Lead on a flat roof is put at "60-100 years" by HomeBuilding, while MyJobQuote's line is that lead flashing "can last for over 80 years", a lower bound. These are ranges for the materials, not promises about a valley.
| Material | Range | Source |
|---|---|---|
| GRP | 25 to 30 / 25 to 40 years | HomeBuilding / Less |
| Lead, flat roof | 60 to 100 years | HomeBuilding |
On cost, MyJobQuote in September 2026 gave a roof valley replacement as "around £540" as a typical UK figure. It does not split that between materials, so it cannot tell you which is dearer on your roof. What moves the price is the length of the valley, the height and access of the work, the state of the boards beneath, and whether the neighbouring slates or tiles survive being lifted and relaid.
Your written price follows the survey, once the valley and the boards under it have been seen.
Where each tends to suit
Lead suits a roof with a traditional character, a tight or unusual valley angle, or a chimney or dormer cheek the valley runs into. It can be shaped to awkward geometry in a way a moulded section cannot, and it pairs with the other leadwork on the roof.
GRP suits a plain, straight valley on a modern or plain-detailed roof, where its smooth channel and low profile do the job. It is not reworked on site the way lead is, so odd angles need a made-to-measure section.
Points to weigh before deciding, in no particular order:
- How long the valley run is and how many bends it has.
- How much of the valley is visible from the street or garden.
- Whether other leadwork on the roof will be left or replaced.
- The condition of the boards, which decide the life of either material.
What matters beyond the material is how it is laid. Overlaps, board condition and the way the tiles are cut and bedded at each side decide whether a valley stays dry. A good installer of either beats a poor one in the other, so ask who will lay it, how the boards beneath are being checked, and what happens to the old valley.
Listed and conservation homes
On a listed house, section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990 means works that change the character need listed building consent. Swapping a lead valley for GRP can change that appearance and the fabric, so the answer is to ask the conservation officer before you decide.
In a conservation area, ask the council whether the change of material matters to it. Whether an Article 4 direction applies to your address is something to check with your own council.
On a listed house the safe course is to keep what was there. A lead valley stays lead, renewed to the specification, unless the council agrees otherwise in writing, and the reasons are the building's character and the paperwork. If consent is needed, it is better to have it before the work than to chase it once the valley is finished.
Related reading, if the valley is already leaking or a full renewal is on the table: lead valley replacement and a leaking lead valley. The overview is lead roofing.
