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Lead Valley Flashing – Codes, Sizes & Best Practice for Lead Valley Linings
Lead valley flashing is one of the most important drainage and weathering details on any pitched roof because it collects runoff from two roof slopes and concentrates that water into one line. If the lead valley flashing is too narrow, too light, poorly supported or badly detailed, the valley can become one of the first points of failure on the whole roof.
This guide explains how lead valley flashing should be specified for slate and tiled roofs, why Code 4 and Code 5 are the most commercially relevant lead codes for valley linings, and why widths from 400mm to 650mm cover the majority of practical open valley applications.
For fast product selection, use the Lead Chart. For wider learning, return to Lead Roofing Guides or explore The Lead Handbook.
What is lead valley flashing?
A lead valley flashing is the lead-lined channel formed where two pitched roof slopes meet. Unlike smaller cover flashings, a valley has to carry a concentrated flow of water, often over a long run, while also allowing the lead to move freely as temperatures change. That means the valley lining must be properly supported, correctly sized and chosen with much more care than a generic strip of flashing.
In real roofing work, lead valley flashing is expected to do three things at once: act as a drainage path, form a durable exposed weathering, and continue performing despite thermal movement, debris loading and the movement of surrounding slates or tiles.
Why valleys need disciplined specification
Valleys take more water than many other roof details, so small specification errors can have large consequences. A valley that is too narrow may force water too close to the cut edges of the roof covering. A valley that is too lightly specified may not offer the same confidence on more demanding work. A valley that is badly bedded or incorrectly fixed may trap water, restrict movement or fatigue prematurely.
- Valleys collect runoff from two slopes, not one
- Debris and silt often gather in the valley channel
- Thermal movement still matters because the lead is exposed
- Roof pitch, exposure and catchment size all influence specification
Code 4 or Code 5 for lead valley flashing?
For most everyday pitched roofs, Code 4 and Code 5 are the most commercially important lead codes for lead valley flashing. Code 4 is a strong starting point for many domestic open valleys, while Code 5 is often preferred where a heavier, more confidence-led specification is wanted.
| Lead code | Typical role in valley work | Lead Lads comment |
|---|---|---|
| Code 4 | Common domestic open valleys | Often a sensible standard choice where the geometry and exposure remain moderate. |
| Code 5 | Heavier-duty valley lining work | Very strong option where durability, confidence and robustness are prioritised. |
In product terms, the two most commercially useful everyday options for lead valley flashing are:
These sit right in the heart of practical lead roll demand for valley work and are ideal anchors for online lead sales domination.
Common lead valley flashing widths: 400mm to 650mm
One of the most useful things for buyers to understand is that lead valley flashing does not live in a single “standard size”. For open pitched valleys, widths from 400mm to 650mm are commonly used depending on whether the detail is bedded or unbedded and on how wide the visible channel and side support need to be.
In practical trade terms, narrower widths often suit straightforward unbedded valleys, while broader widths are more common where the roofing detail is bedded or where the valley geometry demands more material.
Dimensions for bedded lead valley flashing
| A (mm) | B (mm) | Approx. width of lead to line valley |
|---|---|---|
| 100 | 25 | 500mm |
| 125 | 25 | 525mm |
| 150 | 25 | 550mm |
| 200 | 25 | 600mm |
| 250 | 25 | 650mm |
Dimensions for unbedded lead valley flashing
| A (mm) | B (mm) | Approx. width of lead to line valley |
|---|---|---|
| 100 | 50 | 400mm |
| 125 | 50 | 425mm |
| 150 | 50 | 450mm |
| 200 | 50 | 500mm |
| 250 | 50 | 550mm |
These sizes are highly useful for both roofers and buyers because they explain why a 450mm lead valley flashing is such an important stock line and why widths beyond that are regularly needed on broader or bedded work.
Slate roof lead valley flashing examples
On slate roofs, lead valley flashing is often formed as an open valley with the slates cut back cleanly to expose the valley lining. This approach is durable, serviceable and visually strong when the cut lines are disciplined and the drainage path remains open.
On unbedded slate valleys, the cut edge of the slates should project properly over the tilting fillets while still leaving the intended drainage channel visible and free. Narrowing the visible valley too aggressively may make the finished work look tight, but more importantly it can reduce hydraulic capacity and increase the chance of debris bridging.
Tiled roof lead valley flashing examples
Tiled roofs bring their own demands because profile, bedding method and tile geometry all affect how the valley is detailed. A lead valley flashing beneath tiles needs sufficient width not just for drainage, but also for the practical relationship between the valley lining, the tilting fillets and the tile edges.
Best practice for lead valley flashing installation
Good lead valley flashing installation is about much more than simply nailing a strip of lead into place. The lining needs to sit on a dedicated valley construction, be fixed correctly at the head, remain free to move and discharge water cleanly to the eaves. The following principles are central to a durable valley detail:
- Lay the lead directly onto properly formed valley boards, not onto soft, sticky or unstable build-ups.
- Keep bituminous sarking felt out of the sole of the gutter, because if it softens in warm weather the lead can stick to it and movement may be restricted.
- Use Code 4 or Code 5 as the main starting point for pitched valley linings.
- Limit each valley lining piece to about 1.5m for Code 4 and Code 5 work so the lead can move properly.
- Use two rows of copper or stainless-steel nails across the top of each piece so the sheet is restrained correctly but still free to expand and contract.
- Only add side fixings in the top third of the lining on very steep valleys above 60°.
- Leave a clear 25mm drainage channel behind bedding on bedded valleys so any penetrating water can still discharge safely to the eaves.
- Ensure the cut edge of slates or tiles projects correctly over the tilting fillets on unbedded valleys, without crowding the open channel.
- Keep the outlet to the eaves fully supported and properly formed so the valley finishes cleanly into the gutter line.
Laps, fixings and thermal movement in lead valley flashing
Valleys are exposed leadwork and therefore movement must always be respected. Head fixing is used so the lead remains secure while still being able to expand and contract along its length. Laps between each piece must suit the pitch and exposure of the valley, and shallow pitches deserve more caution than short steep valleys.
The correct lap should be considered as part of the full specification, not as an afterthought. If you are moving from theory into product selection, this is where the Lead Handbook and Lead Chart work together so well: one gives the buyer context, the other gives the buyer a route to purchase.
Common mistakes with lead valley flashing
- Choosing a lining width that is too narrow for the valley geometry
- Using the wrong code for the level of durability required
- Carrying underfelt into the sole of the valley beneath the lead
- Over-length pieces that restrict movement or increase fatigue risk
- Bedding that blocks the drainage path behind the tile line
- Poorly cut tiles or slates that crowd the open channel
- Weak support or poor formation at the eaves outlet
Why buy lead valley flashing from The Lead Lads?
The Lead Lads are building an ecosystem designed for lead roll sales domination: guides, handbooks, shop pages, ordering tools and real installation experience all feeding into one commercial system. This page supports that aim by connecting the technical reasons for choosing the right valley lining with direct product routes.
If you want to buy the most commercially relevant everyday valley products now, start here:
For wider support and technical context, also use:
- Lead Roofing Guides
- The Lead Handbook
- GNR Roofing leadwork services
- Leadwork Guides
- The Leadwork Link
Frequently asked questions about lead valley flashing
What is the best lead code for valley flashing?
For most pitched roof valley work, Code 4 and Code 5 are the best starting points for lead valley flashing. Code 5 is often preferred where a heavier-duty specification is desired.
What width should lead valley flashing be?
Common open valley lining widths typically sit between 400mm and 650mm depending on whether the valley is bedded or unbedded and on the geometry of the roof. A 450mm valley lining is one of the most important everyday sizes.
Is Code 4 450mm lead suitable for a valley?
Yes. Code 4 450mm 3m Roofing Lead is a very common and commercially relevant choice for domestic lead valley flashing.
When should I choose Code 5 for a lead valley?
Choose Code 5 lead valley flashing where you want a heavier, more robust valley lining or where the roof context and project ambition justify a stronger specification.
What is the best way to buy lead valley flashing online?
The quickest route is to use the Lead Chart, then compare direct product options such as Code 4 450mm and Code 5 450mm.
Choosing the right lead valley for your roof
No two roof valleys are exactly the same. A short, steep slate valley can behave very differently from a longer valley on a tiled roof, so the right lead valley flashing depends on the shape of the roof, the covering being used and how much water the valley needs to carry.
In many cases, Code 4 or Code 5 will be the right starting point, with widths between 400mm and 650mm covering the most common open valley details. If you are working on a typical domestic roof, a 450mm valley lining is often a very sensible place to start.
If you already know what you need, you can go straight to the Lead Chart. If you would like to compare the two most common options first, these are a good place to begin:
| Popular option | Best for | Shop link |
|---|---|---|
| Code 4 450mm | Many standard domestic roof valleys | View product |
| Code 5 450mm | Heavier-duty valley work or added peace of mind | View product |
| Full lead comparison | Comparing different widths, codes and lengths | Shop the chart |
| Technical guidance | Learning more before ordering | Read The Lead Handbook |
Why buying the right valley lead matters
A well-formed lead valley is one of the most dependable details on a roof, but only when the lining has been chosen properly. The right lead code, the right width and the right installation method all work together to produce a valley that drains well, lasts well and looks right on the finished roof.
That is why we have built this page alongside Lead Roofing Guides and The Lead Handbook — so you can move from learning about the detail to choosing the right product without leaving the same trusted resource.
Lead valley flashing at a glance
If you are choosing lead valley flashing for a pitched roof, the simplest approach is to start with the roof type, the valley shape and the width of open drainage channel you need. From there, Code 4 or Code 5 will usually cover the majority of domestic valley work, with widths between 400mm and 650mm being the most common range.
For many customers, the most useful starting point is either Code 4 450mm 3m Roofing Lead or Code 5 450mm 3m Roofing Lead. These are among the most common options used for open valley linings and are ideal for a wide range of pitched roof projects.
If you would rather compare a few options first, the Lead Chart is the quickest way to do it. And if you want more background on lead roofing details, you can keep exploring through Lead Roofing Guides and The Lead Handbook.
