The short answer
Roofing lead is sold in codes from 3 to 8. Royston Lead's cast-lead brochure gives Code 3 as 1.32 mm, Code 4 as 1.80 mm, Code 5 as 2.24 mm, Code 6 as 2.65 mm, Code 7 as 3.15 mm and Code 8 as 3.55 mm. Each step up is a little thicker and heavier. The right code depends on the job, and the quote should name it.
Every code, in millimetres and kilograms
These are the figures in Royston Lead's cast-lead brochure.
| Code | Thickness | Weight | Colour |
|---|---|---|---|
| 3 | 1.32 mm | 14.97 kg/m² | Green |
| 4 | 1.80 mm | 20.41 kg/m² | Blue |
| 5 | 2.24 mm | 25.40 kg/m² | Red |
| 6 | 2.65 mm | 30.05 kg/m² | Black |
| 7 | 3.15 mm | 35.72 kg/m² | White |
| 8 | 3.55 mm | 40.26 kg/m² | Orange |
The range from the thinnest to the thickest is a little over 2 mm, yet the heaviest code carries more than two and a half times the weight of the lightest per square metre. That weight is real metal on the roof, and it is why timber decks and supports are sized with the code in mind.
Because a code is only a number, a quote that simply says lead tells you nothing. Ask for the code, and ask which part of the roof it is for, so that each area of lead has its own named code and none of it is left to assumption on the day. The same table works as a check when the lead arrives. Our page on lead codes explained goes further into reading them.
What the colour marking is for
Each code in the brochure has a colour: green for Code 3, blue for 4, red for 5, black for 6, white for 7 and orange for 8. The colour is a marking applied by the maker, so that sheets of different thickness cannot be confused on a roof or in a stockroom.
A roofer working with several codes on one job, perhaps a light code for the soakers, a heavier one for the flashings and a heavier one still for a gutter, can pick up the right sheet at a glance. For you, it gives a way to check the delivery or the old lead on the roof against the quote.
The colour tells you nothing else. It is not a quality grade, and it does not mean one code is better than another. Once lead is fixed and weathered the marking is gone, so thickness cannot be read from the colour of an old sheet.
To find the thickness of lead already on a roof, a roofer measures an exposed edge, or compares the sheet with a known piece. We take photographs of the measurement so that you can see it, and we record the result in the survey.
Choosing a code by use
Royston marks five uses with a letter, and gives the codes suggested for each:
- A, soakers: Codes 3 and 4;
- B, flashings: Codes 4, 5 and 6;
- C, pitched valley gutters: Codes 4 to 8;
- D, parapet and box gutters, and tapered valley gutters: Codes 5 to 8;
- E, dormers: Codes 4 to 8.
The pattern is simple: the lightest sheets go on the small hidden pieces and the heaviest go where lead carries water or takes wear. Code 3 is listed for soakers only, and nothing above Code 6 is listed for a flashing, since a flashing is a narrow strip that has to be dressed tightly to brick.
These are the manufacturer's suggestions, and a roofer's judgement on the survey does the rest. The size of the area, how exposed it is, how a gutter drains and whether people will walk on it all count. Our page on Code 4 versus Code 5 looks at the choice that gets asked about most.
Lead sheet roofs follow BS 6915, which Approved Document C cites, so the code and the way it is laid are both worth stating in writing.
What to ask for in a quote
A good quote for leadwork names the code for each area, so each can be checked against the table above. If you are receiving several, make sure each is for the same codes. A lighter sheet costs less and a heavier one costs more, so two totals only compare fairly if the metal matches.
Ask whether the new lead is the same code as the old. Replacing a Code 5 gutter with Code 4 saves a little and gives away some of the wear margin, so there should be a reason.
Ask, too, how the lead will be fixed, since a thick sheet pinned too tightly will split as readily as a thin one, and ask how much movement the detail has been given.
We measure and photograph the existing lead during the survey and name the code for every detail in the quote. The price reaches you as a single written total, and there is no guesswork about what is going onto your roof.
The lead roofing hub explains the rest of the leadwork we carry out in Farnborough, Aldershot and the towns around them.
