The inward corner where two roof slopes join is called a valley. Rain from both slopes pours into it, so the channel carries a heavier flow than the open slope. On many houses around Stroud, that channel is lined with lead: a sheet metal laid along the angle, with the tiles or slates cut to a neat line on either side. Lead suits a valley since it can be bent to the exact shape of the timber below and it lasts for a long time when it is fitted properly.
This guide explains how a lead valley is put together, the particular ways it fails, what the lead code and the length of each piece have to do with it, and what a proper renewal involves. It stays on valleys. For the reasoning behind short pieces of lead in general, see our answer on lead sheet lengths, and for the wider service start at lead roofing.
What a lead valley is, and where you will find one
Two terms first. A lead code is a number that grades lead sheet by thickness, with thicker and heavier sheet carrying a bigger number. Code 4 is 1.80 mm thick and Code 5 is 2.24 mm, according to Leadworx, while Code 8 is 3.55 mm.
You find lead valleys wherever a roof has a change of shape: an L-shaped house, a side extension that meets the main slope, a gabled bay, or a dormer cheek running into the main roof. On a Victorian terrace the valley may be tucked between two small gables facing the street. On a cottage it may sit behind a chimney, out of sight from the lane, which is partly why failures there go unnoticed.
Open, closed or swept
An open valley leaves a band of lead showing between the tile or slate edges. In a closed valley the covering is cut to meet over the lead, which hides below. A swept valley, found on traditional stone roofs, curves the courses round the corner in stone with no metal showing. Cotswold District Council's 2000 stone slate guidance calls lead valleys the cheaper build and a poorer match for a stone roof than a swept one. If you have swept valleys, see Cotswold stone roofing. The rest of this guide covers lead-lined valleys.
How a lead valley gutter is built up
A valley that lasts is made of layers, and each layer has a job.
The support
Boards across the rafters form a smooth, continuous bed. Lead is soft and takes the shape of anything beneath it, so a proud nail head or a gap between boards slowly wears a hole. We want a clean, flat bed before any lead goes on.
The underlay and the lead
A layer of underlay separates the lead from the timber, which lets the metal slide a little as it warms and cools. The lead is laid in lengths from the top of the valley downward, each length overlapping the one below it. The overlap is called a lap, and its job is to stop water running backward and finding the joint. The lead is dressed (shaped by hand with a wooden tool) into the angle, so that it sits tight in the base of the channel and rises up each side.
The edges and the covering
The sides of the lead are held down, not nailed through the face. Fixings go at the top edge, where they are covered by the roof covering, so that no hole is left in the part that carries the water. The tiles or slates are then cut to follow the line of the valley and set clear of the centre, leaving the metal exposed in a strip wide enough to take the flow.
Why lead valleys split, lift and leak
Lead valleys fail for a short list of reasons, and nearly all of them come back to the way the metal moves. Sheet lead expands in sun and shrinks in cold. If a long length is held firmly at both ends, that movement has nowhere to go except into the metal itself, which stretches a little each day and slowly work-hardens until it cracks. This is the same cause behind our answer on why lead cracks.
Lengths that are too long
MyJobQuote's guidance refers to the correct code being fitted in 1.5 metre lengths. A valley laid in a single long run, or with laps that are too small, is the classic cause of a split down the centre line, where the metal is pulled hardest. Short lengths with proper laps let each piece move on its own.
A code that is too light
Royston Lead's chart for cast sheet lists Codes 4 to 8 for a pitched valley gutter, and Codes 5 to 8 for a tapered valley gutter. Code 3 is for soakers only. If a valley was lined in a light code to save money, it is far more likely to dent, tear and wear through where water runs hardest. The right code is a matter of the size of the catchment and the exposure, and we set it out in writing on the quote.
Fixings in the wrong place
A nail through the middle of the lead, a clip that grips the sheet too tightly, or a patch of sealant smeared over a crack: each of these stops the metal moving or opens a path for water. Sealant is a stop-gap and never a repair of the metal beneath.
Debris, moss and foot traffic
Leaves, moss and old mortar pile up in a valley and hold water against the lead. A ladder foot or a boot placed in the centre can crease it. Neither does damage in a day, but over years the creases become weak lines that split.
Reading the signs from the house and the loft
Because the lead sits low between two slopes, you often see the result of a failure before you see the failure itself.
Inside the house
A brown stain that grows at the junction of a ceiling and a sloping wall, a patch of paint that bubbles in the same spot after every storm, or a damp smell in a bedroom beneath a roof angle can all point to a valley. In the loft, the timbers either side of the valley board may be darker and the underlay may show a tide mark.
Outside
From the ground, with binoculars, you can sometimes see:
- tiles or slates along the valley edge that have slipped, chipped or been cut raggedly;
- a build-up of moss, grit or leaves in the channel;
- a bright line or ridge in the lead where it has creased;
- white powdery staining, which is the harmless-looking carbonate that forms on bare lead, and which is explained in our answer on white streaks from lead.
Please do not climb up to look; a foot will crease the lead.
At the survey
We look from a safe position and photograph the valley, the laps and the covering edges, then send you pictures of your own roof. The questions are whether the lead has split along its length or at one lap only, whether the bed beneath is sound, and how far the damage runs. That decides between a repair and lifting the whole valley.
Patch, section repair or full renewal
Not every leaking valley needs stripping. The choice depends on how the lead has failed and how old it is. MyJobQuote's guidance says flashing lead can last for over 80 years when correctly installed, and over 100 years in the higher codes, so an old valley is not automatically a failed one.
When a repair makes sense
A single split at a lap, a puncture from a dropped tool, or a small area of damage on otherwise sound lead can be mended. Done properly, that means cutting out the damaged area, lapping a new piece under the old, and dressing it into the channel. It does not mean a smear of mastic.
When to renew the valley
Renewal is the better answer when:
- the lead is split in several places or along its full length;
- the metal is thin from wear, which you can feel and see where it has gone shiny and rough;
- the original lengths were too long and the same fault will return;
- the boards beneath are rotten or the bed is uneven;
- a re-roof is already planned, since the covering has to come off beside the valley anyway.
If the valley is the only fault on an otherwise sound roof, we price the valley as its own job rather than recommending a larger one.
Where the valley is shared with a stepped wall flashing at the top of the slope, the two details meet, and it is often sensible to look at both at once. Our guide to lead flashing repairs covers the wall side of that junction.
Renewing a lead valley, step by step
Replacing a valley follows an order, and skipping a step is how the next failure begins.
- Access and protection. Scaffold goes up so the work is done safely.
- Lifting the covering. The tiles or slates beside the valley are removed, numbered or stacked in order, and checked for cracks. Any that are damaged are replaced like for like.
- Stripping the old lead. The old lead comes out and the boards below are examined. Rotten boards or battens are cut out and replaced.
- Setting the bed. The surface is cleaned, any projecting fixings are removed, and the underlay is laid.
- Fitting the new lead. The specified code is cut into short lengths, laid from the top downward with proper laps, dressed into the angle and fixed at the edges only.
- Re-laying the covering. The tiles or slates are cut to a clean, even line along the valley and set so the metal is clear of obstruction.
- Finishing. The new lead is treated and the roof is swept clear of offcuts.
Choosing the code
The table below shows where Royston Lead's brochure places each code for valley use.
| Lead code | Thickness | Valley use (Royston, cast lead) |
|---|---|---|
| Code 4 | 1.80 mm | Pitched valley gutter |
| Code 5 | 2.24 mm | Pitched and tapered valley gutters |
| Code 6 | 2.65 mm | Pitched and tapered valley gutters |
| Codes 7 and 8 | 3.15 mm and 3.55 mm | Heavy-duty pitched and tapered valley gutters |
For a valley we generally propose Code 5 or heavier and name the code on the quote. Royston's figures are for cast lead, so treat the table as a guide.
Paperwork, price and what to expect afterwards
Renewing a single valley is a repair in the eyes of the regulations. The Planning Portal says you will not normally need a building control application if less than 25 per cent of the building envelope and less than 50 per cent of the roof is affected. A valley is far below that. If your home is listed, the position is different: listed building consent applies to alterations that affect the building's special interest, and Stroud District Council treats the whole of a listed house as protected. Ask its conservation department first. In a conservation area, check with the planning team if the work changes the look of the roof.
Price
We do not have a sourced national price for a valley on its own, so we do not quote a range here. What we can say is how the price is built. The quote that follows the survey prices each item separately: scaffold, strip-out, replacement boards if needed, lead by code, labour, waste removal and making good, with VAT shown.
After the work
New lead starts bright and weathers to a soft grey. Because it is a target for thieves, see our guide to protecting roof lead from theft explains why it is worth thinking about what a thief can see. We clear the old lead and waste away. The workmanship carries our 10-year guarantee in writing.
A valley should still be looked at once a year. Clear leaves from the channel, check that the tile edges have not moved, and look at the ceiling beneath after heavy rain.