Ask for a lead flashing and a roofer will quickly ask what code you want. The answer matters more than it sounds. A code is the standard way to name the thickness of sheet lead, and every use of lead on a roof, from a hidden soaker to a flat roof covering, has a code it suits. Too thin and the metal splits or stretches. Too thick and it is heavy, costly and harder to shape.
The figures here come from two published sources: Leadworx's guide to lead sheet codes, which gives thickness and weight, and Royston Lead's brochure for cast lead sheet, which gives colour marks and typical uses. Royston's data is for cast lead. Our quick answer on the lead code for flashing picks one code for one job, and this guide lays out the full table beneath it. The wider service is on our lead roofing page.
What the number on a roll of lead tells you
Each code is a whole number, 3 to 8, standing for a band of thickness. As the number rises, so do the thickness and the weight. The system comes from the days when sheet lead was sold by the pound per square foot, and the code number is a rounded echo of that weight. Today the thickness is given in millimetres and the weight in kilograms per square metre, but the code stays as shorthand that every merchant and roofer understands.
What helps a homeowner is knowing that a code is a specification and not a brand name. Code 5 from one supplier is meant to be the same thickness as Code 5 from another, which is why a quote that names the code lets you compare like with like. A quote that says only "lead" leaves the roofer free to choose the thinnest sheet that will pass.
Weight as well as thickness
Lead is dense, so the codes differ in weight more than they look. A square metre of Code 3 weighs 14.97 kg, and a square metre of Code 8 weighs 40.26 kg. On a ten square metre bay roof that is the difference between about 150 kg of metal and about 400 kg, and the deck has to carry it. We come back to that in the last sections.
The full table: Codes 3 to 8
Thickness and weight are from Leadworx. Colour marks and typical uses are from Royston Lead. Royston uses five use classes: A for soakers, B for flashings, C for pitched valley gutters, D for parapet gutters, box gutters and tapered valley gutters, and E for dormers.
| Code | Thickness | Weight | Colour mark | Typical use (Royston classes) |
|---|---|---|---|---|
| 3 | 1.32 mm | 14.97 kg/m² | Green | A: soakers only |
| 4 | 1.80 mm | 20.41 kg/m² | Blue | A, B, C, E |
| 5 | 2.24 mm | 25.40 kg/m² | Red | B, C, D, E |
| 6 | 2.65 mm | 30.10 kg/m² | Black | B, C, D, E |
| 7 | 3.15 mm | 35.72 kg/m² | White | C, D, E |
| 8 | 3.55 mm | 40.26 kg/m² | Orange | C, D, E |
Royston prints Code 6 at 30.05 kg/m², a few grams away from Leadworx's figure, which is the sort of rounding difference you see between suppliers.
Read across a row to see what a code covers. Code 3 is limited to soakers, the small hidden pieces. Code 4 is the only light code that also appears in the flashing, valley and dormer classes. From Code 5 upwards the list drops soakers and adds parapet and box gutters.
Codes 3 and 4: the light end
Code 3 is 1.32 mm thick and green-marked. Royston lists it for soakers alone, and Leadworx describes it as soakers and light duty. A soaker is the small bent piece that goes in alongside each row of slates or tiles at a wall, with the flashing above covering it, so it carries little water and takes little movement. Light metal is enough there, and it keeps the weight and cost down across what can be dozens of pieces on one roof. Our page on lead soakers explains the part itself.
Code 4 as the everyday sheet
Code 4 is blue-marked, 1.80 mm thick. Leadworx says it has turned into the usual pick for ordinary flashings, and Royston lists it across soakers, flashings, pitched valley gutters and dormers. On a roof with well-fixed masonry and sensible lengths of lead, Code 4 is the one a roofer reaches for most.
Where light lead struggles
The risk with thinner codes is stretch. Lead moves with the heat of the day and the chill of the night, and over years a long, thin piece can slowly creep down a slope or crack where it flexes. Code 4 copes with short, well-supported runs. On a long, exposed piece of lead, or one that must be walked on, it can be too light, which is the reason the heavier codes exist.
A flashing renewed in the lightest sheet that will only just do the job is a false economy, and it is the usual reason a repair is needed again.
Codes 5 and 6: the working middle
Code 5 is 2.24 mm, red-marked and 25.40 kg/m². Code 6 is 2.65 mm, black-marked and 30.10 kg/m² on Leadworx's table. Royston's classes for both run across flashings, pitched valley gutters, parapet and box gutters and dormers. Leadworx lists Code 5 for general, vertical and pitched work and Code 6 for large roofs.
This is where most substantial leadwork on a period house lives: a chimney flashing that has to stay put for decades, a valley carrying the run-off from two slopes, a bay roof with an edge that gets leaned on by a window cleaner. Checkatrade's per-metre repair rates are quoted on Code 5, so that is the code behind the national repair prices.
Why valleys and gutters step up
A valley or box gutter takes the water from a whole roof and carries it to one point. It gets more rain, more debris and more standing water than a flashing. That is why Royston moves those uses up to Codes 5 and above, and why a valley is rarely a place to save on thickness. Our page on lead valleys goes through the detail.
Code 6 earns its extra weight on larger runs. The thicker sheet resists stretch over longer lengths, and it tolerates the occasional footstep when someone has to reach a gutter or a chimney across it.
Codes 7 and 8: heavy duty
Code 7 is 3.15 mm, white-marked and 35.72 kg/m². Code 8 is 3.55 mm, orange-marked and 40.26 kg/m². Royston lists both for pitched valley gutters, parapet, box and tapered gutters, and dormers, and both Leadworx entries read heavy duty. Neither appears in Royston's flashing class, and a sheet this thick is also stiff to dress into a mortar joint.
Where the weight goes
Ten square metres of Code 7 weighs about 357 kg, and the same area of Code 8 about 403 kg, against roughly 254 kg for Code 5. That is a real load for a flat roof deck or a gutter bearer. The Planning Portal says Building Regulations approval is needed when a new covering raises the roof's weight by 15 per cent or more, so a structural check is sensible before anyone orders heavy lead.
Long-life work
The thick codes are for the hardest-working places: wide box gutters, parapet gutters on large buildings and roofs where the lead will be walked on. They are rarely needed on a typical house chimney. MyJobQuote puts the life of lead flashing, when it is installed correctly, at over 80 years, and over 100 for the higher codes. Treat that as a typical range, since it assumes good fixing and care.
Matching a code to each part of your roof
Putting Royston's use classes against the codes gives a working map, and a roofer will adjust it to the length, exposure and traffic on your roof.
- Hidden soakers: Code 3 or Code 4. Light sheet is enough because the flashing above does the shedding.
- Flashings at chimneys and walls: Code 4, 5 or 6, with 4 the usual place to begin and 5 where the run is long or exposed.
- Pitched valleys: Code 4 up to 8. Heavier codes suit longer slopes and more water.
- Parapet gutters and box gutters: Code 5 to 8, because they collect and hold the most water.
- Dormer cheeks and tops: Code 4 to 8, depending on size and fixing.
- Bay and porch roofs, flat roofs: the code is set at survey from the size of each bay and what the deck beneath can carry.
Those ranges overlap deliberately. Two sound roofers can choose differently for the same chimney and both be right, which is why a quote should say what was chosen. On a Cotswold stone roof with a swept valley there is no lead valley at all, and the code question moves to the flashings and any lead-lined gutters.
Why the right code matters, and how to check it
The wrong code fails in two directions. Too thin for the job, and the lead stretches, splits at folds and lets water through years before it should. Too thick, and it is awkward to shape, costs more, adds avoidable load and can lift out of a joint that was cut for a lighter sheet. Length matters too. MyJobQuote notes the correct code is fitted in 1.5 metre lengths, because long pieces of lead move more than short ones.
What to ask for
Ask any roofer to name the code against each piece of lead in the quote: soakers, flashings, valleys, bay roofs. A line that says "Code 4 flashing, stepped and apron" tells you far more than "lead work". It also lets you compare quotes fairly, because a Code 5 price and a Code 4 price are for different amounts of metal.
How we choose
At survey we look at the length of each run, how exposed it is, whether anyone will walk on it, and what the structure beneath can carry. The code on the quote follows from that. For a flat roof or a bay roof the deck sets the limit, and our guide to lead flat roofs shows how the codes fit that system. The written quote is itemised line by line, so the cost of stepping up a code is visible.
If you have a quote already, check that it names a code for each piece of lead. We will tell you whether it looks right for the roof in your photographs, and the work we do carries a 10-year workmanship guarantee in writing.