Which lead code is used for valleys?

A valley is the inside corner where two roof slopes meet and drain into each other, as happens where a side extension joins a main roof. Rain from both slopes funnels down that line, so a valley handles more water than any other stretch of a roof. A lead valley gutter is a channel of lead sheet laid in the angle, with tiles or slates lapped over its edges.

Lead suits a valley because it can be shaped into the channel, and because the water is concentrated there, the lining has to be continuous and sound from top to bottom. When a valley leaks, the ceiling beneath it shows the stain quickly, and the timber under the lining can be wet long before that. Our page on lead valley replacement covers the repair side of the same detail, including when relining is better than a patch, and what the work involves from start to finish.

Lead sheet is sold by code, numbered 3 to 8, each code being a fixed thickness with a weight of its own. Royston Lead's brochure on cast lead sheet has a column showing what each is used for. Its category C, a pitched valley gutter, lists codes 4, 5, 6, 7 and 8. Category D, a parapet, box or tapered valley gutter, lists codes 5, 6, 7 and 8. The brochure recommends code 3 for soakers only, so it is not a valley sheet.

In weight, code 4 is 20.41 kg per square metre at 1.80 mm. Code 5 is 25.40 kg at 2.24 mm, code 6 is 30.05 kg at 2.65 mm, code 7 is 35.72 kg at 3.15 mm and code 8 is 40.26 kg at 3.55 mm. Our guide to lead codes sets out the same range with its uses, and the page on lead sheet weight goes through the figures in a table you can keep.

The brochure gives a range, not a single answer, because valleys differ. Several things bear on the choice. A long valley that collects water from a big roof is asked to do more than a short one beside a dormer. A shallow valley carries water away more slowly than a steep one, so overflow is more likely. A valley that people may need to walk along for maintenance suffers more wear than one nobody touches.

Heavier lead is stiffer and stands up better to dents, but it is harder to work into the angle and costs more to buy. A lighter code costs less and bends easily, yet it may wear sooner where use is heavy. Lead must also be cut in lengths that allow for movement with temperature, so each piece can shift. A roofer weighs all of this on the actual roof, standing at the valley, and not from a table in the van. The table gives the range the maker supports; the survey picks the point within it.

A box gutter runs in the gap between two roofs, or along the foot of a parapet wall, and has flat sides, often with a gentle fall along its length. A tapered valley changes width as it runs. Royston lists both under category D with codes 5 to 8, so code 4, which the brochure does list for pitched valleys, does not appear against these.

These gutters hold more standing water and take more load, and a leak is harder to reach and trace. They deserve a careful detail with proper falls, which means the water has somewhere to go instead of sitting in the lining. Where you have an old box gutter that keeps overflowing, the survey includes photographs of the outlet and the lining, and we tell you whether it can be repaired or needs renewing, and what each route would involve for the rooms beneath.

You should not have to guess which code you are being sold. The written quote follows the survey, names the lead code for each detail and gives a single total price. If a quote simply says lead, ask which code and why. A roofer should be able to explain the choice in plain words, with the valley in front of you, and to say why a neighbouring detail uses a different code.

Checkatrade's roof repair guide, updated October 2026, lists lead flashing repairs at £50 to £70 per metre, plus VAT. A full valley renewal costs more, because the covering on both sides has to be lifted and relaid. For the wider subject, see the lead roofing and leadwork hub. If you have a valley that is stained or dripping, photograph the ceiling and tell us roughly where it runs, which helps us bring the right materials to the survey.