The Short Answer: What Should Be on Your Roof?
If you just want to check a quote you have in front of you right now, here is the rule of thumb I use on every job:
- Code 3 (Green): Underneath tiles only. Suitable for small concealed hip and abutment soakers that are sheltered from direct sun. Never let anyone dress Code 3 onto the outside of a chimney or into a valley.
- Code 4 (Blue): The domestic standard for flashings. Essential for chimney step flashings, apron flashings, dormer cheeks, and pitched roof valleys on standard houses.
- Code 5 (Red): Heavy-duty valleys, back gutters & heritage roofs. Used for wide valley troughs, deep chimney back gutters, shared parapet gutters on Victorian terraces, and conservation properties.
Understanding BS EN 12588 Lead Codes and Colour Wrappers
In the UK roofing trade, genuine rolled lead sheet is manufactured to British Standard BS EN 12588. This standard guarantees that the lead has been rolled between heavy steel mills to an exact, uniform thickness all the way through the roll—which is why tradespeople call it milled lead.
Historically, lead was measured in imperial weight (pounds per square foot). A sheet weighing 4lb per square foot became known as "Code 4", 5lb became "Code 5", and so on. Today we measure thickness in millimetres, but the code numbers and the colour-coded plastic wrappers on the rolls remain the exact way we verify material on site.
| Lead Code | Wrapper Colour | Thickness (mm) | Max Piece Length | Correct Roof Application |
|---|---|---|---|---|
| Code 3 | Green | 1.32 mm | 1.00 metre | Concealed tile/slate soakers only |
| Code 4 | Blue | 1.80 mm | 1.50 metres | Chimney step & cover flashings, aprons, standard valleys, dormer sills |
| Code 5 | Red | 2.24 mm | 1.50 metres | Main valley gutters, deep chimney back gutters, parapet gutters, heritage roofs |
| Code 6 | Black | 2.65 mm | 1.50 metres | Large flat lead bays, wide commercial/church box gutters |
Tip when works start: When a roofer unloads materials onto your driveway or scaffolding, glance at the plastic packaging on the lead rolls. If you have paid for Code 4 chimney flashings and Code 5 valleys, you should see Blue and Red rolls—not Green.
Why Code 3 Lead Fails When Used for Chimney Flashings
Lead is a brilliant, malleable metal, but it expands and contracts noticeably whenever the temperature changes. On a sunny afternoon in summer, lead sitting on dark slate or clay tiles can heat up rapidly and expand. When the sun drops or rain hits it, it cools and contracts.
Because Code 3 lead is only 1.32mm thick, it lacks the structural body to push and pull its own weight back and forth when exposed to direct sunlight. Instead of expanding evenly along its length, thin Code 3 lead buckles, ripples, and suffers from metal fatigue. Within a few winters, hairline splits open up right along the crease where the lead turns into the brickwork or down the centre of the valley.
Soakers—the small L-shaped pieces of lead that sit underneath each course of plain tiles or slates against a wall—are shaded from direct sun by the tiles above them and are cut into tiny pieces (usually 175mm to 250mm long). Because they are small and shaded, thermal movement is tiny, making Code 3 ideal for soakers. For everything exposed to the sky, you need Code 4 or Code 5.
Code 4 vs Code 5: Where Each One Belongs on Your Roof
Homeowners often ask if they need to pay extra for Code 5 everywhere, or if Code 4 will do the job. Over my thirty years working on roofs around Sittingbourne, Faversham, and the Medway Towns, I specify the code according to the job that specific piece of lead has to do:
Where Code 4 is Spot On
- • Chimney Step & Cover Flashings: Dressed over Code 3 soakers and chased 25mm into the brickwork mortar joints.
- • Front Apron Flashings: Dressed over the front face of a chimney stack or conservatory abutment wall.
- • Dormer Cheeks & Sills: Weathering the sides and front sill of pitched roof dormers.
- • Standard Domestic Valleys: Where two modest roof pitches meet on a standard semi-detached or terraced house.
Where You Should Upgrade to Code 5
- • Chimney Back Gutters: The horizontal trough behind a chimney stack takes the full brunt of water running down the upper roof slope and needs to be bossed (shaped) without thinning out too much.
- • Long or Steep Roof Valleys: Particularly on tall Victorian slate pitches or steep Kent peg tile roofs where heavy rainwater scours the metal.
- • Parapet & Shared Box Gutters: Common on period terraces where you walk in the gutter to clear leaves.
- • Coastal & Conservation Work: Exposed roofs near the Swale or Thames estuary, and heritage buildings in conservation zones.
Why Fitting Details Matter Just as Much as Thickness
Buying a roll of Code 4 or Code 5 lead is only half the battle. Even the thickest milled lead will split if a roofer installs it in one long continuous strip or cements it rigid so it cannot move. When I survey a leaking chimney or valley that was only replaced five years ago, it is almost always down to one of three installation shortcuts:
- Pieces cut longer than 1.5 metres: Under BS EN 12588 and Lead Sheet Training Academy (LSTA) guidelines, no individual piece of Code 4 or Code 5 flashing should exceed 1.5 metres in length. If an abutment wall is 4.5 metres long, it must be fitted in three overlapping sections (with at least a 100mm lap) so each piece can expand and contract freely.
- No lead clips in windy spots: On exposed roofs—especially properties catching winds off the coast around Sheerness, Whitstable, or open farmland—the bottom edge of cover flashings must be held down with stainless steel or copper clips. Without them, winter gales flip the lead upwards.
- Shallow mortar chases or smeared silicone: Flashing should be turned at least 25mm into the brickwork joint, wedged firmly with lead wedges (not bits of broken tile or timber), and pointed neatly. Simply smearing silicone sealant against flat brickwork is not a flashing—it will peel away within a year.
Checklist: 5 Questions to Ask Before Accepting a Leadwork Quote
If you are getting quotes for leadwork and flashings, chimney repairs, or lead valley repairs, ask your roofer to put these five details in writing on the estimate:
- 1. "Which BS EN 12588 Code of lead is included?" Look for Code 4 (minimum) on external flashings and Code 4 or 5 on valleys and back gutters. Beware of cheap cast or unbranded imported sheet, or adhesive "lead-replacement" flashing tape unless you have specifically asked for a synthetic alternative.
- 2. "Are the concealed soakers being replaced too?" Sometimes a leak down a chimney breast is caused by corroded or missing Code 3 soakers underneath the tiles, not just the visible step flashing on top.
- 3. "Will the lead be treated with patination oil?" Freshly installed milled lead develops a powdery white carbonate stain when rain first hits it, which washes down onto your tiles and brickwork. Wiping a coat of patination oil onto the new lead immediately after fitting stops unsightly white streaks and helps an even grey patina form.
- 4. "Is safe access included?" You cannot accurately chase out brickwork, dress heavy Code 5 lead into a back gutter, and repoint a tall chimney stack balanced one-handed off a ladder. Check whether staging or scaffolding is included.
- 5. "Who will actually be doing the lead dressing?" Lead bossing and dressing takes patience and practice. When you instruct C.L. Baker, I survey and carry out the work myself—I never pass your roof onto subcontractors.