Understanding Lead Codes in the UK
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Understanding Lead Codes: Code 4 vs Code 5 for Roofing Applications
- Lead codes refer to the thickness and weight of lead sheet, with higher numbers indicating heavier gauge material.
- The current BSEN 12588:2006 standard uses colour codes to classify lead sheet. The old imperial numeric system (Code 3, Code 4, Code 5 etc.) is still widely used by the trade in the UK.
- Code 4 lead = Code Blue lead: thickness 1.75–1.80 mm, approximately 20.41 kg per square metre. The standard choice for most lead flashing applications on domestic roofs.
- Code 5 lead = Code Red lead: thickness 2.00–2.24 mm, approximately 25.51 kg per square metre. Specified where greater durability or longer service life is needed.
- Abbey Metals also stocks Code Yellow lead (1.50 mm) which is BSEN 12588:2006 grade with no old numeric equivalent that can replace Code Blue / Code 4 in certain flashing applications, offering a material and therefore cost saving.
- The right code depends on the application, exposure level, and the width of lead being used.
- All codes are stocked by Abbey Metals UK and available for fast UK delivery.
When you are specifying lead for a roofing project, understanding Code 4 lead and Code 5 lead is essential. These codes are not arbitrary labels. They tell you the thickness, weight, and appropriate use of the material before a single piece is cut or fixed. What many contractors may not realise is that the familiar numeric system, Code 3, Code 4, Code 5 and so on, has been updated by a colour-coded classification under the current BSEN 12588:2006 standard. Abbey Metals stocks and references lead by these colour designations. Understanding both systems will help you specify correctly and order with confidence.
What Do Lead Codes Actually Mean?
Lead sheet in the UK is classified by a system that indicates its thickness and mass per square metre. The older imperial system used numeric codes running from Code 3 through to Code 8, with each step up representing a heavier, thicker sheet. The current standard, BSEN 12588:2006 replaces those numeric codes with colour designations. The two systems largely correspond to each other, but they are not identical in every detail. Abbey Metals has published a full lead sizing comparison guide showing how the colour codes and old numeric codes map to each other, along with thickness ranges, typical uses, and the over-specification saving each colour code offers.
The Full Colour Code System at a Glance
| Colour Code | Old Numeric Code | Thickness (mm) | Typical Use |
|---|---|---|---|
| Code Green | Code 3 | 1.25–1.32 mm | Soakers |
| Code Yellow | No equivalent | 1.50–1.59 mm | Flashings (can replace Code Blue / Code 4 in certain applications) |
| Code Blue | Code 4 | 1.75–1.80 mm | Flashings and sheet |
| Code Red | Code 5 | 2.00–2.24 mm | Sheet |
| Code Black | Code 6 | 2.50–2.65 mm | Sheet |
| Code White | Code 7 | 3.00–3.15 mm | Sheet |
| Code Orange | Code 8 | 3.50–3.55 mm | Sheet |
Source: Abbey Metals Lead Sizing Comparison Guide. Standard: BSEN 12588:2006.
Why the Colour Codes Matter for Specification
Abbey Metals' lead sizing guide shows the over-specification cost saving for each grade: the percentage by which the old numeric code exceeds the minimum usable thickness within the same colour band. For Code Red / Code 5, that saving is 12%. For Code Blue / Code 4, it is 2.9%. This means that in some applications, specifying correctly to the colour code rather than defaulting to the old numeric maximum can represent a genuine material saving without any compromise on performance.
Code 4 Lead (Code Blue): The Standard Choice for Most Flashing Work
Code 4 lead, correctly referred to as Code Blue lead under BSEN 12588:2006, is the workhorse of the roofing trade. It accounts for the majority of lead flashing on roof installations across the UK, and for good reason. It offers the right balance of workability and durability for most domestic and light commercial applications.
Where Code 4 / Code Blue Lead Is Typically Specified
You will find Code 4 / Code Blue lead used across a wide range of standard roofing tasks:
- Step flashing and soakers on pitched roofs where tiles or slates meet a wall
- Chimney back gutters and front aprons on domestic properties
- Valley linings on pitched roofs with moderate exposure
- Abutment flashings where a roof meets a vertical surface
The 300 mm wide roll is one of the most commonly ordered formats. If you want more detail on that specific size, our post on Code 4 Lead 300mm: Specifications and Best Uses covers dimensions, tolerances, and typical applications in full.
Could Code Yellow Lead Be an Alternative to Code 4?
One option worth knowing about is Code Yellow lead a grade that has no equivalent in the old numeric system. At 1.50mm thick, it sits between Code Green (Code 3) and Code Blue (Code 4) in the range. Code Yellow can replace Code Blue / Code 4 lead in certain flashing applications, with an over-specification saving of up to 20% compared with ordering to the old Code 4 nominal.
Code 5 Lead (Code Red): When You Need Greater Mass and Durability
Code 5 lead, correctly referred to as Code Red lead under BSEN 12588:2006, is the next step up from Code Blue. The extra thickness makes a meaningful difference in applications where the lead is exposed to more stress, wider widths, or more severe weather. Under the BSEN colour code system, Code Red is 2.00 mm thick, whereas tje old numeric Code 5 has a thickness of 2.24 mm meaning there is a 12% over-specification saving available when ordering to Code Red rather than defaulting to the old Code 5 maximum.
Where Code 5 / Code Red Lead Is Typically Specified
Code 5 / Code Red lead is the right choice in several situations:
- Wider flat roof coverings where Code 4 / Code Blue would exceed maximum width limits
- Parapet and box gutters that need to handle greater volumes of water
- Exposed locations such as coastal buildings or high-altitude roofs where wind and thermal movement are more extreme
- Lead roof coverings on flat or low-pitch roofs where longevity is the primary consideration
- Ridges and hips on pitched roofs where a longer service life is specified
Code 4 vs Code 5: A Direct Comparison
Choosing between Code Yellow, Code 4 (Code Blue) or Code 5 (Code Red) comes down to the specifics of your project. Neither code is inherently better. Each is right for different applications. Code 4 / Code Blue lead is lighter and easier to dress into complex shapes, which makes it preferred for detailed flashing work. It is also lower in cost per linear metre, which matters on projects where lead flashing is used in high volumes. As noted above, Code Yellow may offer a further material saving in suitable flashing applications. Code 5 / Code Red lead gives you greater resistance to wear, thermal stress, and mechanical damage. If you are unsure which code applies to your specific detail, the safest approach is to consult Abbey Metals who can advise on code selection based on your application and the dimensions you are working to. You can also refer to the Abbey Metals lead sizing comparison guide for a quick reference on how colour codes and old numeric codes relate to each other.
Lead Flashing Alternatives and When They Apply
Some projects do use lead flashing alternatives such as self-adhesive butyl or aluminium-based products. These are common in situations where cost, weight, or planning restrictions on heritage buildings make traditional lead impractical. That said, no lead alternative flashing product fully replicates the longevity, workability, or aesthetic of genuine lead sheet. For permanent roofwork where a 50-year or longer service life is expected, Code 4 / Code Blue or Code 5 / Code Red lead sheet remains the material of choice for most roofing contractors and surveyors in the UK. For a broader look at flashing materials and installation guidance, see our post: The Complete Guide to Lead Flashing for UK Roofing Projects.
- Under BSEN 12588:2006, lead is classified by colour code. Code 4 = Code Blue (1.75–1.80 mm). Code 5 = Code Red (2.00–2.24 mm). The old numeric codes are still widely used in the trade but the colour designations are the correct technical reference.
- Code Blue / Code 4 lead is the standard specification for most domestic lead flashing applications.
- Code Red / Code 5 lead is specified for wider bays, exposed locations, flat lead roofs, and applications requiring longer service life.
- Code Yellow lead (1.50 mm, no old numeric equivalent) can replace Code Blue / Code 4 in certain flashing applications and may offer a material saving of up to 20%.
- Width limits for each code are set by Lead Sheet Association guidance. Exceeding them without stepping up in code leads to early failure.
- All codes are available from Abbey Metals UK in standard roll widths with fast UK delivery. See the full sizing comparison guide for a complete overview.
- When in doubt about which code to specify, contact a specialist supplier before ordering.
Frequently Asked Questions
Code 4 lead, known as Code Blue under BSEN 12588:2006, has a thickness of 1.75–1.80 mm. Code 5 lead, known as Code Red, has a thickness of 2.00–2.24 mm and is heavier and more durable. Code Red is suitable for wider applications and more exposed locations where Code Blue would not perform as well over time. Ordering to the BSEN colour code rather than the old numeric maximum can offer a material cost saving, particularly on Code Red where the saving is around 12% or up to 20% if Code Yellow can be used.
Code Yellow is a grade set out by BSEN 12588:2006 with a thickness of 1.50mm. It has no equivalent in the old imperial numeric system. Abbey Metals stocks Code Yellow lead, and it can be used to replace Code Blue / Code 4 in certain flashing applications. The potential over-specification saving versus the old Code 4 nominal is up to 20%. If you are considering Code Yellow as an alternative for a specific detail, speak with the Abbey Metals team to confirm suitability before ordering.
Code Blue / Code 4 lead is used on flat roofs, but the maximum bay width is limited by Lead Sheet Association guidelines. If your flat roof requires wider bays or is in an exposed location, Code Red / Code 5 is the correct specification. Using the wrong code for the width of bay is a common cause of cracking and premature failure in flat lead roofwork.
300mm Code 4 lead refers to a roll of Code Blue lead sheet (the current BSEN 12588:2006 designation for what was called Code 4) cut to 300 mm wide. This is one of the most common widths ordered for chimney flashings, abutment details, and step flashing on pitched roofs. The 300 mm width suits many standard domestic flashing applications and stays within the safe width limits for Code Blue material.
Correctly installed lead flashing, specified at the right code for the application, is expected to last 60 years or more. Premature failure is usually caused by incorrect code selection, bay widths that exceed the recommended limits, or inadequate fixings and detailing rather than a fault with the material itself.
Where Code Red / Code 5 is the correct specification, it is always worth using. The additional material cost is modest compared to the cost of stripping and relaying lead work that has failed prematurely. For applications such as flat roof coverings, parapet gutters, or wider valley linings, Code Red gives you the service life the project requires. For standard domestic flashing details, Code Blue / Code 4 is the appropriate choice and there is no benefit to stepping up unnecessarily.
Abbey Metals stocks the full range of BSEN 12588:2006 lead sheet: Code Green, Code Yellow, Code Blue, Code Red and beyond in a range of roll widths, ready for fast UK delivery. All Abbey Metals lead is 100% Barmark-free, carries a 50-year guarantee, and is made from 80% recycled content. Whether you are ordering for a single domestic job or a larger contract, our team is here to help you get the right material at the right specification. View the full lead sizing comparison guide or get in touch with Abbey Metals UK today to discuss your requirements or request a quote.