The short answer
Code 4 is the everyday grade for most flashing, and Code 5 is the common step up for chimneys, abutments and anything exposed. Code 3 is for soakers only, and heavier codes such as 6 are kept for larger or more exposed pieces. The piece, its width and its position decide, which is why a written quote names the code for each flashing.
What the code number measures
A lead code is a thickness grade for rolled sheet. The higher the number, the thicker and heavier the lead. Leadworx explains that the codes comply with BS EN 12588, the standard for rolled lead sheet used in building, and sheet is traditionally marked with a colour for each code so it can be told apart on a roof.
| Grade | Sheet thickness | Weight for each square metre | Marker colour |
|---|---|---|---|
| 3 | 1.32 mm | 14.97 kg | Green |
| 4 | 1.80 mm | 20.41 kg | Blue |
| 5 | 2.24 mm | 25.40 kg | Red |
| 6 | 2.65 mm | 30.10 kg | Black |
The figures come from the Leadworx code guide and Royston's cast lead brochure. Cast and rolled sheet differ slightly in weight, but the thickness grades line up.
Which code suits which piece of leadwork
Royston's table sets out typical uses, starting with Code 3, which it recommends for soakers alone. A soaker is a little L-shaped sheet of lead slipped beneath a slate or tile course at the point a roof butts a wall, and it can be thin because it is hidden and short. Code 4 is listed for four jobs: soakers, flashings, dormers and pitched valleys. Codes 5 and 6 are listed for flashings, valleys and dormers, and Code 5 upwards for parapet and box gutters, where the lead carries a heavy flow of water.
Leadworx names Code 4 as its standard grade for ordinary flashing jobs. In practice that covers a plain wall flashing on a modern house. Chimney aprons, long runs, tall stepped flashings and exposed positions tend to justify Code 5, because the extra thickness stands up better to movement and weather. Our page on lead soakers goes into the small pieces in more detail.
Matching the grade to the building and its exposure
A tall chimney on a ridge line meets wind and rain from every side, and the lead around it works harder than a flashing on a low wall in the lee of a neighbouring house. For that reason a roofer looks at where the piece sits as well as how big it is. A stack that stands clear of the roofline, a wall facing the prevailing weather, or a flashing on a roof that is hard to reach for later repairs all lean toward the heavier grade.
Older buildings add another consideration. A Victorian terrace or a chapel may have lead that has already done many decades, and the replacement is expected to do the same. Choosing a sensible grade at the start costs a little more per metre and saves a second visit. The rest of our lead roofing pages show the other places where code choice comes up, from valleys to dormers.
Why soakers are a special case
Soakers are the one piece where the lightest grade is the norm. Each is cut to a set size, bent into an L, and slid under a course so that one leg lies on the roof and the other turns up the wall. Because it is bent once and then hidden by the slate above, there is less need for stiffness. Our page on lead soakers covers fitting in more detail.
Soakers still need care when a roof is re-covered. They are reused if they are in good order, and replaced if they are cracked or have been bent back and forth more than once. A new covering over old soakers is a common cause of a repeat leak.
Is a thicker code always better?
Not automatically. A heavier sheet is stiffer, harder to dress tightly into corners and over profiled tiles, and it costs more per metre. A flashing that does not sit tight to its surface lets wind and water behind it, however thick the lead may be. Equally, a grade that is too thin for its position can crack at the folds, and a repair on it rarely lasts.
The width of the piece matters as much as the code. A narrow strip tucked into a sheltered corner can take a lighter grade than a wide apron across an exposed chimney. The skill is in choosing the grade that suits the job rather than the heaviest one on the merchant's shelf. Where the sheet will be pointed into masonry, the way it is fixed is covered in our page on repointing lead flashing.
Code, lifespan and national price guides
MyJobQuote reports that lead flashing installed correctly can run beyond 80 years, with higher codes passing 100. Those figures assume good workmanship and ordinary wear, so read them as typical ranges rather than promises.
On price, Checkatrade's roof repair guide for October 2026 gives Code 5 lead flashing, up to 150 mm wide, at £50 to £70 per metre, and stepped flashing at £80 to £120 per metre, both excluding VAT. They are national typical figures, and a chimney or a long wall run on a real roof also brings access costs. Whichever quotes you hold, look for VAT and scaffolding being included, and for the grade of lead being named.
Finding out what code is on your roof
From the ground you cannot tell, and a ladder inspection by an owner is not worth the risk. A roofer can read the thickness at a lifted edge or a corner, and sometimes an old offcut left in the loft carries the colour mark. Thin lead beside a chimney gets checked early in any survey we do.
The survey photographs show the flashings up close, and the written quote names the code proposed for each one. Where the grade is right and only the pointing has failed, the smaller job is the better one. Lead has also raised safety questions for homeowners, and our page on whether lead roofing is safe answers them. The work is guaranteed for ten years in writing, and you can reach us on 01793 626096 or WhatsApp.