The short answer
Code 4 is the standard choice for general lead flashing, according to Leadworx. At 1.80 mm thick it is the sheet most roofers reach for at walls and chimneys. Code 3 is thinner and is used for soakers, the small hidden pieces. Heavier codes, 5 and above, go to gutters, flat roofs and exposed or large pieces where more metal is needed.
Code 4 for general flashing
The code number stands for thickness. Code 4 is 1.80 mm thick and weighs 20.41 kg per square metre, with a blue colour mark on the roll, according to Leadworx and Royston Lead. Leadworx calls it the everyday sheet for flashing, and Royston's typical-use list puts it across soakers, flashings, valleys on a pitch and dormer work.
The reason it suits flashings is a balance. A flashing at a chimney or a gable wall is a narrow strip, held in place along its top edge and moving only a little. Code 4 is strong enough to resist wind and creep over such short pieces, light enough to dress cleanly into a stepped line, and cheaper than the heavier sheets.
Where a flashing is long, exposed to lifting wind or likely to be stepped on by a sweep or an aerial fitter, a step up to Code 5 is reasonable. We decide that on the day from what we see at the wall, not from a rule that applies to every house. The colour mark on the roll lets you check what arrives: Royston lists green for Code 3, blue for Code 4 and red for Code 5, so a quick look at the roll in the van tells you whether the sheet matches the quote. It is a small check, and it takes seconds.
Code 3 for soakers
Soakers are little folded lead sheets laid along the side of a slated or tiled slope where it abuts a wall. One goes in with each course, and the flashing above is dressed down over them. Water that gets past the flashing runs on the soaker and out onto the covering below, so the soaker is hidden and does not take weather directly.
Code 3 is 1.32 mm thick, weighs 14.97 kg per square metre and is marked green. Royston lists it for soakers only, and Leadworx describes it for soakers and light duty. Because a roof can have dozens of soakers, the lighter sheet matters for weight and cost. Our answer on what lead soakers do describes the part itself.
Do not be tempted to use Code 3 for the visible flashing. It is thinner than the job calls for, and it is the sort of saving that returns as a repair.
Heavier codes for gutters and exposed lead
As the code goes up, so do thickness and weight. Royston's typical-use classes show the pattern. Code 5 is listed for flashing, for parapet and box gutters, for valleys on a pitch and for dormers, whereas Codes 7 and 8 drop ordinary flashing from the list and keep the gutters and dormers.
| Job | Code usually used |
|---|---|
| Soakers | Code 3 |
| General flashing at walls and chimneys | Code 4 |
| Flashing needing more strength, pitched valleys | Code 5 |
| Parapet and box gutters, tapered valleys | Code 5 and above |
Code 5 is 2.24 mm and red-marked. Code 6 is 2.65 mm, Code 7 is 3.15 mm and Code 8 is 3.55 mm. Parapet and box gutters collect water from a large area and carry it through the wall, so a thicker sheet earns its weight. The full table, with colours, is in our guide to lead sheet codes 3 to 8.
Why the wrong code costs you later
A sheet thinner than its position demands will stretch, then split, then wear through along its folds. MyJobQuote's figure for a correctly installed flashing is over 80 years, rising past 100 on the higher codes, which shows how much the choice matters over a long period. Thicker lead has more to give before it fails.
The opposite error is less common but real. A heavy code on a small flashing is harder to dress into a stepped line and tends to spring back from sharp folds, so the finish is worse. A quote that names the right code for each part beats a quote that uses one thickness everywhere.
Length links to code. MyJobQuote's guidance is the correct code in 1.5 metre lengths, so a thicker sheet does not excuse a long piece. If you want to see how the pieces are fixed at the top, read about pointing lead flashing.
What to look for on a quote
Check that the code is written against each item: soakers, stepped flashing, back gutter and any valley. A quote that says only "lead" gives the roofer room to use the thinnest sheet that will pass on the day.
MyJobQuote's 2026 guide has a chimney flashing patch at £150 to £250; its average for a full replacement is £570. Checkatrade gives Code 5 lead flashing repairs at £50 to £70 per metre and stepped flashing at £80 to £120 per metre, excluding VAT. Treat these as national guide ranges; access and the length of the run move a real figure.
After the survey we send a written quote with the code named for each part and every line priced, and at the end we sweep the site and carry the waste off. Because the code is named per item, you can hold the finished work up against the quote line by line. The finished work comes with a 10-year workmanship guarantee in writing. Browse more on lead roofing or send a photograph of your flashing through the form, and we will say which code we expect to use.