A valley is the one place on a pitched roof where all the water gathers. Every slate or tile on both slopes sheds towards it, so the strip of lead at the bottom of the fold is doing the work of a gutter and a roof covering at once. It is a narrow strip, hidden from the pavement, and on many houses nobody has looked at it for years. When it fails, the leak is typically sharp: a brown mark that appears in the ceiling below a hip or an internal corner of the roof after heavy rain. This guide explains the two main types, open and closed, shows how a lead valley is built and what makes it leak, and sets out how a valley is relined. It will help you read a survey report and ask a roofer the right questions before the scaffold goes up.
Open and closed valleys
There are two basic ways to treat a valley, and the difference is whether you can see the lead.
In an open valley, the lead lies exposed in the fold, with bare metal visible down the fold, flanked by the slate or tile cut-lines. You can look down on it from a ladder and see its condition. The width of the exposed strip depends on the roof and the covering, and it is a design choice as well as a practical one. A wider channel copes with more water and clears debris more easily. A narrow one looks neater but blocks sooner.
In a closed valley, the slates or tiles from both slopes are cut and carried across the fold so they meet in a line, covering the lead entirely. From the ground it looks as though the two slopes simply join. The lead is still there, lying beneath the courses as a continuous gutter, but it is hidden. A related form, the secret gutter, is covered on our page about the secret gutter. Some roofs have a swept valley, where slate courses curve round the fold, a feature of traditional slating that depends on cutting each slate to a curve.
Closed valleys trade visibility for neatness. They keep the lead out of the weather and out of sight, which many owners and conservation officers prefer. They are also harder to inspect and slower to repair, because reaching the metal means lifting courses of slate. An open valley shows its faults early, a closed one only when the water arrives indoors.
Valleys are not all the same shape either. Some run straight from ridge to eaves. Others are short, cut across a small dormer or an extension. Some are very shallow in pitch. The pitch matters for the lead, because the steeper the valley, the more the sheet tends to creep down it over time as it warms and cools.
How a lead valley is built
Beneath the lead is a firm bed. On many older roofs that is a pair of boards laid along the fold, sometimes with a timber called a tilting fillet on each side to lift the first course of slates so they sit clear of the metal. The boards must be flat and sound, with no raised nail heads, because the lead lies directly on them over an underlay that stops it rubbing.
The lead is laid in lengths, starting at the bottom and working up, with each upper piece lapping over the lower. The lap is the joint, and it relies on gravity and the width of the overlap, not on any sealant. The sheet must be wide enough to run well up under the roof covering on each side. If the lead is too narrow, water driven by wind can run across the channel, over the edge and under the slates.
The code of the sheet is part of the specification. Supplier data for cast lead gives code 4 for pitched valley gutters, with code 5 and above for valleys that carry more water, and heavier codes still for the largest. The same data suggests a maximum piece length for a pitched valley gutter of about 1,500 mm. Both figures are a trade guide and not a rule for your roof, which is why we set the code and the length of each piece out on site. Our guide to lead codes explains the grading in full.
Fixing is the last detail. The lead is held at the top with a clip or a fixing in the overlap, and is never nailed through the exposed face, because every hole is a path for water. The metal must be left free to slide a little as it expands and contracts.
Why a lead valley leaks
Lead is durable, and cost guides put a figure of over 80 years on well-installed flashings. A valley that is leaking has usually been let down by its details, not by the age of the sheet.
Cracks and creep
On a steep valley, lead moves downhill as it heats and cools, a slow slide that stretches the metal at the bottom and wrinkles it at the top. Eventually it cracks, often across the width at a fold. Our guide to why lead cracks goes through the causes.
Debris and blocked channels
Moss, leaves and grit settle in a valley and hold moisture against the lead. In an open valley, the build-up forces water out sideways beneath the slates. In a closed one, debris at the foot can back water up the channel.
Lead too narrow, laps too short
A valley that was relined in a hurry with lead cut too narrow, or with shallow laps, lets water in during a storm. It looks fine on a dry day and fails in wind-driven rain.
Slipped or broken roof covering
When a slate or tile beside the valley slips, it exposes the lead edge and the timber beneath. Water gets behind the metal and soaks the boards.
Rot beneath
Boards left damp for years soften. The lead above loses its support and can tear when anyone steps on it.
Poor repairs
Tape, sealant and bitumen can hold a split for a season. They collect dirt, hide the real fault and make a lasting repair harder.
Where leaks occur in a valley, the damp often appears some distance away, because the water runs along a rafter before it drips. Our page on a roof valley leak gives a method for tracing it.
Spotting trouble from the ground and the loft
A valley's condition can be guessed at without leaving the ground. A few checks tell you whether to ask for a survey.
- Stand back and look along the roof with binoculars. In an open valley, check the lead for wrinkles, splits and bright patches where the surface has worn.
- Look for green or black growth along the line of the fold. It shows where moisture is lingering.
- Check the slates or tiles beside the valley for slips and cracks. Any gap at the edge of the lead is a path for water.
- In the loft, look at the timbers beneath the fold during or soon after rain. A dark, damp patch on the boards or on a rafter close to the valley line is a strong sign.
- Look at the ceilings under the valley for stains, especially after storms.
Do not walk on a valley. Lead is soft, and a single foot can kink the sheet and open a seam. It is also a dangerous place to stand, since the channel runs down the steepest part of the roof.
A valley leak can resemble other faults. A chimney flashing, a failed hip and a slipped slate can all give a similar stain on the same ceiling. That is why we trace a leak back to the point of entry, and do not guess from the stain alone. Where the answer is simple, such as a blocked channel or a lifted edge, the repair is small. Where the lead has crept or cracked along its length, the repair is a relining.
For an older house, the valley sits within a larger system, so the survey takes in the neighbouring parts too. Our box gutter guide describes the flat-bottomed channel that sometimes sits where two roofs meet, and the way to tell it from a V-shaped valley.
Relining a valley on a slate or tile roof
When a valley needs relining, the work follows a settled order.
- Access. A ladder is not enough for a valley of any length. Scaffold or a roof platform gives a safe working position and somewhere to put materials.
- Lift the covering. Slates or tiles on each side are removed for a margin wide enough to take the new lead, and sorted. Natural slate that is sound is kept and reused, and we match anything that has to be replaced.
- Strip the old lead and check the bed. The boards are examined, rotten ones cut out and replaced, and any raised fixings cleared.
- Fit the underlay and the new lead. The sheet is laid from the bottom upwards with laps set to the pitch, dressed into the fold without stretching, and fixed at the top edge only.
- Restore the covering. The slates or tiles are re-laid over the lead edges. In a closed valley they are cut and mitred to meet in a neat line.
- Test. Where possible we check the result with water or in the next rain.
Lead is the traditional metal for the job and it matches the metal already on an older house, but it is not the only choice. Where lead is not wanted, other materials are used, and we explain the options and the effect on a listed building in our page about lead alternatives on listed buildings.
Matching matters on older roofs. A valley relined in a heavy code, with clean laps and fresh slate cut to the original pattern, should look like a part of the roof. A valley relined in a different style stands out for years.
Once we have surveyed, you get a written fixed figure that names the code of lead, the length of each bay and whether the valley boards beneath need renewing. Typical UK figures for leadwork are gathered in our leadwork cost guide, which also notes that there is no published national price for a valley.
Consent, regulations and what comes first
Start by checking the status of the house. The World Heritage designation covers all of Bath, while the city-wide conservation area reaches roughly half of it. On a listed house, work touching its character calls for consent from B&NES Council under a separate regime to planning, and doing it without is an offence, so contact the council before anything is booked.
Relining in matching lead is the sort of repair conservation officers expect. Changes are what raise questions: swapping lead for another material, converting a closed valley to an open one, or altering the line of the slates. Ask first if you are considering any of these.
Building Regulations are a separate matter, with thresholds. The Planning Portal sets out when roof work needs approval, and a single valley sits far below those limits. If the valley is part of a larger re-roof, the rules may apply to the job as a whole. We raise this at the survey and deal with the notification where it is needed.
If you suspect a valley is leaking, a few practical steps help. Photograph the stain and note when it appears, so the pattern shows whether it follows rain, wind or snow melt. Place a bucket if water is dripping, and move belongings away. Keep off the roof. Then arrange a survey, because the longer a valley leaks, the more of the board and rafter it soaks. Leaks come first with us: we make the roof safe, then plan the lasting repair.
The lead roofing service page covers the wider range of leadwork, including flashings and gutters.