The Difference Between Code 3 and Code 4 Lead Flashing
For centuries, lead flashing has been used in roofing to prevent water from entering the internal structure through a joint. The earliest utilisation of lead for waterproofing is believed to be during the Norman era, when historical buildings used lead roof coverings to keep out rain and decrease water ingress from chimneys, vent pipes, walls that abut roofs, and window and door openings. Lead is now an integral part of any roofing system for waterproofing buildings and properties, and it comes in different types, weights, and lead flashing codes.
What do the codes mean in lead flashing?
Lead coils and sheets are assigned different codes in the UK, ranging from 3 to 8, to ensure they are fit for purpose, so homeowners and building contractors can select the right type of lead roof flashing depending on their requirements. Each lead flashing code refers to the lead’s thickness (or weight) suitable for different roof sections to provide adequate water protection.
The importance of using the right lead flashing codes
Depending on the building's construction and structure, different roof components have diverse requirements and weight limitations. Also, lead, like any metal, shrinks upon cooling and expands upon heating, resulting in natural wear and tear over time. As a result, lead flashing codes are important for identifying the right thickness or the appropriate weight load of lead waterproofing membrane for your roofing needs.
Choosing the right lead flashing ensures a longer lifespan and flexibility of the material for your needs while providing complete water protection. In contrast, using the wrong thickness can result in poor installation, early wear and tear of lead flashing, water ingress and potential damp issues like rotting, mould, and mildew growth.
Code 3 vs Code 4 Lead Flashing: What's the Difference?
The main difference between code 3 and code 4 lead flashing is the thickness of the material. Code 3 lead flashing coil has a thickness of 1.32mm and a weight of 14.97 kg per m², whereas code 4 lead has a thickness of 1.80mm and a weight of 20.41 kg per m².
The code 3 lead is the thinnest flashing coil or sheet available in the market and is suitable for fitting abutment soakers against a chimney stack or wall. However, aside from soakers, code 3 lead may not be fitted on other roof systems. If you want more robust water protection, you will need a higher code flashing, such as code 4 lead, which has a much wider application than code 3. Code 4 is generally the industry-standard for sealing and waterproofing soakers, pitched valley gutters, dormers, and vertical cladding.
Aside from codes 3 and 4, there are additional codes for lead flashing coils and sheets that vary in thickness and are used to seal different roofing systems. But which one should you go with? It ultimately depends on the type of project, your budget and where the lead flashing will be used. For example, code 8 is the highest code available for lead flashings, which is ideal for flat roofs where standing water is more common. In the table below, you will find a list of different lead flashing codes that may help you find the right one that works best for your project. Also, check out this article if you need guidance on how to install or repair roof flashing.
Different lead flashing codes and where to use them
| Code | Thickness (mm) | Weight (Kg/m²) | Recommended for |
| Code 3 | 1.32 | 14.97 | Soakers |
| Code 4 | 1.80 | 20.41 | Soakers, flashings, pitched valley gutters, dormers, vertical cladding |
| Code 5 | 2.24 | 25.40 | Flashings, pitched valley gutters, tapered valley gutters, dormers, vertical cladding, flat roofs |
| Code 6 | 2.65 | 30.05 | Flashings, pitched valley gutters, tapered valley gutters, dormers, flat roofs |
| Code 7 | 3.15 | 35.72 |
Pitched valley gutters, tapered valley gutters, dormers, flat roofs |
| Code 8 | 3.55 | 40.26 | Pitched valley gutters, tapered valley gutters, dormers, flat roofs |
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