The short answer
The lead code is the standard UK measure of how thick and heavy a sheet of rolled lead is, running from Code 3 to Code 8 — the higher the number, the thicker the lead. The three most common domestic codes are Code 3 (1.32mm, about 15 kg/m²), used for soakers and lighter work; Code 4 (1.80mm, about 20 kg/m²), the versatile workhorse used for most flashings, valleys and dormers; and Code 5 (2.24mm, about 25 kg/m²), used for flashings, valleys and flat or pitched lead roofs where more durability is needed. Heavier Code 6, 7 and 8 are used for larger lead roofs and gutters. The codes follow the British Standard for rolled lead sheet (BS EN 12588) and the recommendations of the Lead Sheet Association.
If a quote says 'Code 4 flashing' and you are not sure what that means, this is the page. Knowing the codes helps you check the right lead is being used for the job.
Common lead codes
- Code 31.32mm — soakers, light work
- Code 41.80mm — most flashings & valleys
- Code 52.24mm — flashings, valleys, roofs
- Code 6–8heavier roofs & gutters
- StandardBS EN 12588 / Lead Sheet Association
What the code numbers mean
The code is simply a thickness-and-weight grade: each step up adds lead, so it is sturdier and more durable but heavier and dearer. The codes are colour-coded on the sheet for identification on site. The three you will meet most on a house are Code 3, 4 and 5, with the heavier codes reserved for full lead roofs, large gutters and bays.
| Code | Thickness | Approx. weight | Typical use |
|---|---|---|---|
| Code 3 | 1.32mm | ~15 kg/m² | soakers, lowest-profile work |
| Code 4 | 1.80mm | ~20 kg/m² | flashings, valleys, dormers, cladding |
| Code 5 | 2.24mm | ~25 kg/m² | flashings, valleys, flat & pitched roofs |
| Code 6–8 | thicker still | heavier | larger lead roofs, gutters, bays |
To BS EN 12588 and Lead Sheet Association guidance. Source: Roofing Superstore lead code guide.
Which code for which job
- Soakers: Code 3 is the usual choice because its lower profile sits neatly between tiles or slates.
- Flashings: Code 4 covers most domestic flashing, with Code 5 where extra durability or longer runs are wanted.
- Valleys: Code 4 or Code 5, depending on the valley type and width.
- Lead roofs & large gutters: Code 5 and up, with bay sizes also governed by the code to avoid the lead splitting from thermal movement.
Want the right code specified for your job?
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Frequently asked questions
What is the difference between Code 3, 4 and 5 lead?
They are thickness grades: Code 3 is 1.32mm (about 15 kg/m²), Code 4 is 1.80mm (about 20 kg/m²) and Code 5 is 2.24mm (about 25 kg/m²). The higher the number, the thicker and more durable the lead.
Which lead code is used for flashing?
Most domestic flashing uses Code 4, with Code 5 where extra durability or longer runs are needed. Code 3 is generally reserved for soakers because of its lower profile.
What standard do lead codes follow?
UK lead codes follow the British Standard for rolled lead sheet, BS EN 12588, and the recommendations of the Lead Sheet Association, which set out the correct code and bay size for each application.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific roof. They are guidance, not a quotation.