Every piece of sheet lead on a roof has a code, and the code decides how thick it is, how heavy it is and what job it can be trusted with. The number is not a quality grade. Code 3 is not a poor lead and code 8 is not a better one. They are the same metal rolled to different thicknesses, and the skill lies in matching the thickness to the detail. A soaker tucked under a slate can be thin because it is small and sheltered. A box gutter that carries the run-off from a whole roof slope needs a heavier sheet because it moves, wears and holds water. This guide explains what a lead code is, sets out the thickness and weight for each one, and shows which codes are normally used for soakers, flashings, valleys, gutters and flat roofs. It also covers how to read a quote and what to ask your roofer to confirm in writing before the lead goes on.
What a lead code actually is
A lead code is the number given to a thickness of rolled lead sheet. The lead is made to the British and European standard BS EN 12588, and the sheet is stamped or marked so that anyone on the roof can tell which code it is. Codes run from 3 to 8, and the higher the number, the thicker and heavier the sheet.
The code also has a colour. Manufacturers mark the sheet with a coloured stripe or a colour on the wrapping so that a delivery can be checked at a glance. Code 3 is green, code 4 is blue, code 5 is red, code 6 is black, code 7 is white and code 8 is orange. The colour marks come from a lead manufacturer's brochure, and a roofer who knows the system will check them on arrival, because a pallet of the wrong code is easy to send back on the day and expensive to discover later.
Behind the number is a plain physical fact. Lead expands when the sun warms it and contracts when it cools. Fix a long sheet rigidly at each end and it creeps a little with every warm day, never quite coming back, until it cracks. Thicker lead resists that stretching better, up to a point, which is one reason the heavier codes are specified for the bigger and more exposed details. Another reason is simple wear. Water running down a gutter, foot traffic during maintenance and the grit that collects in a valley all scour the surface, so a gutter has more metal to lose than a flashing does.
Lead has been used on roofs for centuries, so you will sometimes hear older weights described in pounds per square foot. The code system replaced that way of talking. If a surveyor or an older drawing quotes a weight in pounds, ask your roofer to translate it into a code, so that the quote, the delivery and the finished work all use the same language. It takes a minute, and it removes a whole class of disagreement about what was supposed to be fitted.
Thickness and weight for each code
The table below gives the thickness and the weight for each code. The figures are from Leadworx's published explanation of the codes, and the colours from a lead manufacturer's brochure. Treat them as typical figures. The sheet you receive will be marked, and the supplier's own data sheet is what to check against.
| Code | Thickness | Weight per m² | Colour mark |
|---|---|---|---|
| 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 |
| 7 | 3.15 mm | 35.72 kg | White |
| 8 | 3.55 mm | 40.26 kg | Orange |
Look at the weight column and the practical side becomes clear. A square metre of code 8 weighs almost three times as much as a square metre of code 3. On a small flashing that difference is a few kilos. On a flat roof of several square metres it is a load that the deck and the joists have to carry, and they carry it each day, year after year. A heavier code is not free: it costs more to buy, more to carry up, more to fix and more to dress into shape.
The thickness column matters at the edges. Lead is dressed by hand into corners and over mouldings, and a thick sheet fights back. Code 8 is hard to form tightly around a small detail, while code 4 or 5 folds easily. That is why you do not see the heaviest codes used on intricate flashings, even though they would last longer as a flat sheet.
There is one more reason to know the table. When a quote lists a weight rather than a code, you can use the column above to turn it back into a code and then into a thickness, which tells you whether two quotes are offering the same metal.
Soakers and flashings: codes 3, 4 and 5
A soaker is a folded square of lead, tucked beneath each slate or tile with its other half rising against the masonry, one for every course beside an abutment or chimney. A flashing is the lead strip laid across the top of those upstands to close the gap between wall and roof, so rain cannot track behind the covering.
Supplier guidance treats these as the lighter end of the range. Code 3 is listed for soakers only, because a soaker is small, sheltered and covered by the slates above it. Code 4 serves both soakers and flashings, along with pitched valley gutters and dormer cheeks. Code 5 is the general choice for flashings, valleys and gutters, and it is the code many roofers reach for when the detail is exposed or the roof is old and the fixings are not what they were.
Where you see code 4 or code 5 on flashings, the maximum piece length is the next limit that matters. The manufacturer's brochure gives 1,500 mm as the longest piece for flashings and pitched valley gutters in codes 4 and 5. Longer than that and the lead moves too far in the heat and starts to ripple and tear at the fixings. A long wall abutment is therefore built from several lengths, each lapped over the next, rather than one long strip. We go through how those laps and wedges work on our page about lead flashings and soakers.
One further point about flashings is easy to miss. The wedges that hold a cover flashing in a joint in the wall are placed at a maximum of 500 mm apart, according to the Lead Sheet Association. A thin code on a long flashing with wide wedge spacing will lift in a gale, so the code and the fixing are chosen together. The same logic applies to the soakers beneath: a soaker that is too short for the slate or tile it serves leaves a path for water, however good the lead is.
Valleys, parapet gutters and box gutters: codes 5 to 8
A valley is the trough formed at the meeting line of two sloping planes of roof, and lead lines it to carry both slopes' run-off to the eaves. A parapet gutter collects water in a lead-covered channel behind the low wall that rises at the roof edge. A box gutter performs that task from a sunken timber trough tucked between two roofs or hard against a taller wall. Behind a Georgian stone parapet in Bath, the parapet gutter is often the part of the roof that does the most work and gets the least attention.
These details carry more water, for longer, than any flashing. The supplier's guidance lists code 5 and code 6 for parapet, box and tapered gutters, and codes 7 and 8 for pitched valleys, parapet gutters and box gutters where a heavier sheet is wanted. Code 4 appears for pitched valleys on a steep, simple roof, where the slope is short and the volume of water is modest.
Why choose the higher codes? A gutter is flat or only slightly sloped, so water lingers, debris sits and the lead is always damp. It is also walked on during maintenance and cleared with a trowel and a brush. The thicker sheet has more metal to give up before it wears through, and it resists the daily stretch and shrink better across a longer run.
A flat-bottomed gutter must also fall to its outlet. The recommended minimum fall for flat roofing is 1:80, and good practice is to design to 1:40 so that the finished fall still reaches 1:80 after construction tolerances and deflection (BS 6229, quoted by manufacturers). A heavy code does not make up for a gutter that holds water. Standing water is where lead corrodes, where dirt builds and where the first split tends to open.
If your gutter is leaking, the cause is often a fault at a joint, a drip or the outlet rather than the code itself. Our page on a lead valley shows what we look for in the first inspection, and the same habits of looking apply to a parapet or box gutter.
Flat roofs and bay roofs: where thickness meets span
A lead flat roof is a sheet roof, and the code is tied to how far a sheet can run before it needs a joint. Flat roofs of 10 degrees or less are laid in bays between joints. The joints across the fall are drips, which are small steps in the deck, and the joints along the fall are rolls, which are shaped timber battens that the lead is dressed over. The manufacturer's brochure shows the maximum distance between drips increasing as the code goes up, so a heavier code allows a longer bay before the sheet is stopped by a step.
That does not mean the heaviest code is always the right one. The weight is carried by the deck, the bay layout follows the shape of the roof, and the cost rises. On a small bay window or porch roof, a code 5 or code 6 sheet laid in short bays is often the sensible answer, since the bays are short anyway. On a larger flat roof, the choice of code is made alongside the spacing of the rolls and drips, and the decision is a design one, not a catalogue one.
Cost is part of the picture. Typical UK ranges from MyBuilder's flat roof cost guide (2026) put a lead flat roof at £150 to £200 or more per square metre. A heavier code adds metal and therefore cost, but a thin code that fails early adds a repair bill that outweighs the saving. The price we put in writing after the survey names the code for each part of the roof.
The layout of rolls, drips and bays is covered on our page about a lead flat roof, and period bays and porches have their own page in our guide to lead bay roofs.
Reading a quote and checking the delivery
A good lead quote names the code for each part of the job. A line that reads only "lead flashings and gutters" tells you nothing. A line that reads "code 4 soakers, code 5 flashings, code 6 to the parapet gutter" tells you what you are buying and lets you compare two quotes fairly.
What to ask for in writing
Ask which code is proposed for each detail, and why. A sensible answer refers to the length of the run, the exposure, the pitch and the existing lead. If the existing lead is a different weight from the new, ask whether the difference is deliberate. On a listed house, ask whether the code has been agreed with the B&NES conservation team, as a change in appearance or material needs the right consent.
What to check on the day
The rolls arrive marked. The colour stripe or the printed code on the wrapping should match the quote, and the rolls should not be stacked in a way that crushes the edges. A roofer who shows you the stripe before cutting is a roofer who expects the question.
Lifespan and what protects it
Correctly installed lead lasts a very long time. MyJobQuote's leadwork guide (2026) gives flashing as over 80 years, and over 100 years for the higher codes, and Less gives 50 to 100 years for lead flat roofs. These are typical figures that depend on exposure and workmanship, never promises. Where lead fails early, the cause is usually the detail: a sheet too long, a missing drip, poor fixing or a gutter that does not drain. We cover that on our page about how long lead lasts.
When a quote arrives, check that each detail has its code written beside it, and when the lead is delivered, the code is printed or colour-marked on the roll, so you can match the two yourself. For the wider picture of the work, start from our lead roofing service.