Demystifying Roofing Lead: The Definitive Guide to Code 3, Code 4, and Code 5

When it comes to weatherproofing a property, nothing matches the proven longevity of rolled lead sheet. However, as any experienced roofer or builder knows, using the wrong gauge can lead to catastrophic failures, either through premature cracking due to thermal movement or lifting under high winds.

To ensure your next roofing project is fully compliant with modern building regulations, you need a precise understanding of the traditional numeric coding system. All high calibre rolled lead is manufactured in strict accordance with BS EN 12588, which regulates thickness tolerances and chemical consistency.

The number assigned to the lead code historically relates to its weight in pounds per square foot (e.g., Code 4 weighs 4lb per square foot). Today, we measure this via precise nominal millimeter thicknesses and kilograms per square metre. Let’s break down the exact specifications and mandatory trade uses for Code 3, Code 4, and Code 5.

Code 3 (Green Label) – The Soaker Standard

Code 3 is the thinnest and lightest of the main architectural lead sheets. Because of its reduced mass, it is highly malleable but lacks the structural rigidity to withstand direct, open exposure to harsh weather elements.

• Thickness: 1.32mm
• Weight: 14.97 kg/m²
• Primary Uses: Exclusively for soakers interleaved between slates or tiles, or light duty concealed applications where the lead is entirely protected by an overlapping layer of a heavier code.
• The Golden Rule: Never use Code 3 for exposed flashings, chimney aprons, or valley linings. Its thin profile means it will quickly buckle, pucker, and lift when exposed to the UK's typical freeze-thaw cycles and heavy wind loads.

Code 4 (Blue Label) – The Roofing Workhorse

Code 4 is universally recognised as the industry standard for general domestic roofing applications. It strikes the perfect engineering balance: heavy enough to resist wind uplift and thermal fatigue, yet flexible enough to dress smoothly over complex brickwork and tile profiles.

• Thickness: 1.80mm
• Weight: 20.41 kg/m²
• Primary Uses: General cover flashings, stepped flashings, chimney aprons, chimney backs, hip and ridge details, and pitched valley linings.
• The Golden Rule: While incredibly versatile, Code 4 must be cut to the correct maximum length during installation. To prevent thermal cracking as the metal expands and contracts, individual flashing lengths should never exceed 1.5 metres.

Code 5 (Red Label) – The Heavy Duty Specialist

When a project demands heightened durability, wider dimensions, or faces severe weather exposure, Code 5 is the professional's choice. It provides a thicker, more robust barrier that handles significantly higher mechanical and thermal stress.

• Thickness: 2.24mm
• Weight: 25.40 kg/m²
• Primary Uses: Flat roofing, large box gutters, parapet linings, tapered valley gutters, dormer cheeks, and wide weather-exposed flashings.
• The Golden Rule: Because of its increased thickness, Code 5 allows for greater structural movement. You can increase your maximum bay installation length up to 2.0 metres between mechanical joints, making it highly efficient for larger commercial or prestige residential properties. 

Quick Reference Specification Table

Pro Installer Tip: No matter which code you install, always apply a high quality patination oil immediately after installation. This stops the initial white carbonate staining (lead tracking) from running down the roof tiles and protects the material while it naturally develops its dark grey protective patina. Please see our Guide to Patination Oil

To view our range of Roofing Lead and Flashing, click the link below:

Roofing Lead and Flashing