Code 4 Lead 300mm: Specifications and Best Uses

Code 4 lead at 300mm wide is one of the most common specifications in UK roofing. It covers the majority of standard flashing details on pitched roofs, from chimney abutments to dormer cheeks. Before you order, it is worth understanding how the old numeric code system relates to the colour codes used by Abbey Metals under BSEN 12588:2006, and whether Code Yellow might be a better fit for your job.

Numeric Codes vs Colour Codes: What Is the Difference?

The traditional Code 3, Code 4, Code 5 numbering system is widely used across the roofing trade, but it is not the current British Standard reference. BSEN 12588:2006 replaced numeric codes with colour codes, and Abbey Metals supplies lead to the colour code standard. The two systems map across as follows for the grades most relevant to flashing work.

• Code Green = Code 3, thickness 1.25mm to 1.32mm, used for soakers
• Code Yellow = no numeric equivalent, thickness 1.50mm to 1.59mm, used for flashings
• Code Blue = Code 4, thickness 1.75mm to 1.80mm, used for flashings and sheet
• Code Red = Code 5, thickness 2.00mm to 2.24mm, used for sheet

The key point here is Code Yellow. It has no old numeric equivalent, which means many roofers and specifiers are not aware of it. It sits between Code 3 and Code 4, and it is a viable alternative to Code Blue for a number of standard flashing applications. Choosing Code Yellow where it is appropriate reduces material weight and cost without compromising performance.

For a fuller comparison of Code Blue and Code Red across roofing applications, see our guide Understanding Lead Codes: Code 4 vs Code 5 for Roofing Applications.

Code Blue (Code 4) at 300mm: Key Specifications

Code Blue lead at 300mm is defined by the following properties under BSEN 12588:2006.

• Thickness: 1.75mm 
• Colour identification: Blue
• Typical use: flashings and sheet work
• Available in 3m and 6m lengths at a variety of widths including 300mm.

Why 300mm Is a Common Width for Flashing Work

300mm is one of the most widely ordered widths for lead flashing, alongside 150mm and 240mm. The right width for your job depends on the detail you are working to.

A typical cover flashing or step flashing detail requires a minimum 75mm upstand into the wall or mortar joint, plus a minimum 150mm weathering lap over the roof surface. That gives a minimum working width of 225mm for most standard flashing runs. 300mm gives additional tolerance for dressing, lapping, and variation in the substrate, which is why many roofers prefer it as a default.

Wider widths suit larger details such as parapet flashings or back gutters where a single piece needs to cover a greater span. Narrower widths such as 150mm are used for soakers and smaller repair details. If you are not sure which width fits your job, measure the upstand and lap required at the junction and add a working margin before ordering.

Code Yellow vs Code Blue at 300mm: Which Should You Order?

This is a question worth asking before every flashing job. Code Yellow at 1.50mm is lighter and more affordable than Code Blue at 1.80mm. The BSEN 12588:2006 standard recognises Code Yellow as suitable for flashings, and Abbey Metals stocks it for this purpose.

Code Yellow at 300mm is appropriate for standard step flashing, cover flashing, and most abutment details on domestic pitched roofs where the lead is not subject to foot traffic or high mechanical stress. If your specification calls for Code 4 and you are using it for flashings rather than sheet work, Code Yellow is worth considering.

Code Blue remains the right choice where a heavier gauge is specified, where the detail involves a wider or longer run, or where the job requires sheet-grade lead rather than flashing-grade. If you are in any doubt, contact the Abbey Metals team before ordering.

Best Applications for Code Blue 300mm Lead

Step Flashing

Step flashing runs up a pitched roof alongside a wall or chimney, with individual pieces overlapped at each course of tiles or slates. Code Blue at 300mm is the standard for this detail. Each piece should be at least 150mm long, with the upstand tucked into the mortar joint or raked out and re-pointed over the lead. Code Yellow at 300mm is also suitable for step flashing where the specification allows.

Cover Flashing

Cover flashing is dressed over soakers to form a weathertight junction at roof abutments. A 300mm width gives enough material to form a proper upstand and lap in one piece. Code Blue is the standard specification here. Where soakers are used beneath, Code Green is the correct grade for the soakers themselves.

Chimney Flashing

Chimney flashings involve a front apron, back gutter, and two runs of step flashing around the stack. Code Blue at 300mm suits the step and cover elements. The back gutter may require wider or heavier lead depending on the chimney size and roof pitch. We will soon be publishing a guide entitled Lead Code 5: When to Specify Heavier Gauge Lead for Roofing for guidance on when Code Red is the right call.

Dormer and Abutment Details

Dormer cheeks and wall abutments follow the same principles as chimney flashing. Code Blue at 300mm covers most standard step and cover details. For professional guidance on the full range of leadwork details involved in dormer and abutment work, watch this space for our post Professional Roof Leadwork: Installation Guide for UK Roofers.

Handling and Fixing Lead at 300mm

Lead dresses readily around angles and into chases. Use a bossing mallet and dresser to form internal and external angles without creasing the material. Avoid over-working lead in cold conditions as it becomes less pliable at low temperatures.

Fix lead flashing using lead clips or wedges at the top of chases, not with nails through the face. Nailing through the face creates stress points and leads to cracking over time. Where the lead is tucked into a mortar joint, use a purpose-made leadwork sealant to secure the upstand once dressed. Limit continuous runs to 1.5 metres to allow for thermal movement.

For full installation guidance, read How to Install Lead Flashing on Roof: Step-by-Step Guide.

Frequently Asked Questions