#Proper Leadwork: Lead Codes Decoded (3–8) for Flashings, Hollow Rolls & Bay Sizing
Correct lead code selection is the foundation of #proper leadwork. Choose the wrong code and you risk
splits, ripples, nail pops, ponding or premature failure. Choose the right code and your flashings, bays, hollow rolls and gutters work with thermal movement rather than fighting it.
This practical guide explains Codes 3–8 in plain language, shows where each belongs, and gives you simple, standards-aligned checks before you buy or install.
Get Lead Lads Services & Prices
Lead Lads Standards Hub
GNR Roofing: Leadwork Authority
Regulatory Standards (BS6915)
This article is part of our “Proper Leadwork: Technical Series”. It includes tables, worked examples, and a printable checklist.
1) What are lead codes?
Lead sheet “codes” label the thickness and weight of rolled lead. In the UK, Codes 3–8 are common.
Lead code selection is the process of matching the code to the application (e.g., flashing, bay, gutter), the span, the fall, and the exposure.
As code number increases, so does thickness, weight and stiffness. Thicker isn’t always better: too heavy for a small flashing can over-stress masonry chases and make movement control harder; too light for a wide bay can lead to fatigue and splits.
Standards alignment: use this guide alongside BS 6915 (code selection, detailing and fixings) and good practice notes (e.g., LSTA). See our
Leadwork Standards hub and
GNR Roofing’s regulatory standards overview.
2) Core principles of lead code selection
- Movement first. Lead expands and contracts with temperature. Both the length and width of a piece must allow for movement and drainage.
- Match stiffness to task. Flashings need conformity and light restraint (often Code 4). Wider, flatter bays need more stiffness (Code 5–6+).
- Keep pieces modest. Smaller panels and proper laps beat over-wide single sheets. Bay sizing limits are not optional.
- Fix appropriately. Use correct clips, straps and fasteners (copper or stainless), set out to restrain but not pinch movement.
- Support matters. Underlay and deck build-up (cold vs warm) affect condensation risk and surface temperatures.
- Detail for water. Falls, drips and outlets take priority. Overflows are a safety valve, not an afterthought.
3) Code thickness & typical uses (quick table)
| Code | Approx. Thickness | Typical Uses | Notes |
|---|---|---|---|
| Code 3 | ~1.32 mm | Soakers on pitched roofs, light flashings in low-exposure zones | Light, easy to form; not for broad surfaces or long lengths |
| Code 4 | ~1.80 mm | Step/cover flashings, chimneys (with soakers), small abutments | Most common flashing code; check upstand and chase details |
| Code 5 | ~2.24 mm | Bays, dormers, parapet gutters, wider flashings, hollow rolls | Good stiffness for moderate spans and exposed zones |
| Code 6 | ~2.65 mm | Valleys, broad bays, parapet/box gutters, heritage roofs | Greater resistance to fatigue; heavier to handle |
| Code 7 | ~3.15 mm | Very wide bays, high exposure parapets, heritage cornices | Use when spans/traffic demand extra stiffness |
| Code 8 | ~3.55 mm | Exceptional spans, heavy-duty heritage applications | Specialist work; plan handling and fixings carefully |
4) Movement, restraint & lap rules (why code choice matters)
Temperature swings drive movement. The stiffer the sheet (higher code), the more force it can exert on fixings and adjacent materials if movement is not controlled. Therefore, lead code selection goes hand-in-hand with correct clip spacing, lap lengths and bay sizes.
- Laps. Follow standards for minimum head/side laps and drip dimensions; increase with exposure and lower falls.
- Clips & straps. Fix to restrain uplift and creep but allow sliding movement. Use copper or stainless steel.
- Upstands & chases. Provide adequate height above finished surface and proper chase depth, with compatible mortar or sealant.
- Drainage first. Do not allow ponding. Falls and drip edges prevent water dwell time that accelerates fatigue.
Need a refresher on standards? Visit the
Lead Lads Standards hub or GNR’s
BS 6915 overview.
5) Bay sizing by code, fall & exposure
Bay sizing limits exist to control movement and fatigue. As a rule, keep widths modest and introduce drips/rolls at sensible centres. In exposed locations (coastal, upland), lean towards higher codes or reduced centres.
Indicative bay width limits
| Application | Typical Codes | Indicative Max Bay Width |
|---|---|---|
| Flat/low-slope bays | 5–7 | 500–750 mm (reduce in high exposure) |
| Parapet/box gutters | 5–7 | Up to ~600–800 mm (falls ≥ 1:80) |
| Dormer roofs | 5–6 | 450–600 mm typical |
| Valleys | 6–7 | By flow; use sumps/outlets for capacity |
Drips, falls & centres
- Falls: Design adequate falls; avoid dead-flat. Increase falls where debris risk exists.
- Drips: Provide regular drips to break sheets into smaller bays; improve drainage and reduce fatigue.
- Centres: In higher codes, drips/rolls at tighter centres can limit stress accumulation.
Remember: the “right” lead code selection often pairs with a smarter layout (more drips/rolls) rather than simply jumping to a heavier code.
6) Flashings: step, cover, chimney & soakers
Flashings are the most visible showcase of #proper leadwork. They must conform neatly to surface irregularities, sit correctly in the chase, and move without tearing or loosening. That’s why lead code selection here is crucial.
Typical flashings by code
| Detail | Typical Code | Why |
|---|---|---|
| Step flashings (brick/stone) | Code 4 | Flexible enough to boss neat steps; sufficient durability |
| Cover flashings to abutments | Code 4–5 | Code 4 common; Code 5 where exposure or width increases |
| Chimney aprons & back gutters | Code 4–5 (with soakers often Code 3–4) | Balance stiffness with formability; respect movement joints |
| Soakers (slate/tile interfaces) | Code 3–4 | Thin, light, and unobtrusive; sized to pitch and covering |
For chimneys, sequence matters: soakers, side flashings, apron, then back gutter. Keep laps consistent and chase depths sufficient. Mortar or sealant must be compatible and not brittle. In very exposed locations, consider stepping up one code or tightening centres.
7) Hollow rolls & wood rolls
Hollow roll caps are a hallmark of traditional lead roofing. They control movement, add stiffness and form a visual rhythm across the roof. Lead code selection for rolled work usually starts at Code 5 for general applications, moving to Code 6 where spans increase or exposure is severe.
- Centres: Keep roll centres consistent (e.g., 450–600 mm typical). Tighten in exposed sites.
- Fixing: Use proper clips/straps at specified spacing; do not over-tighten—allow sliding.
- Detail: Neat bossing at roll ends and junctions prevents stress raisers and capillary traps.
8) Gutters, valleys & parapets
Gutters concentrate water. The combination of water loads, debris, and thermal cycling demands robust sheets and smart detailing. Consequently, lead code selection for gutters often sits at Code 5–6, rising to 7 in special cases.
- Falls: Provide consistent falls (e.g., ≥ 1:80) and manage long runs with intermediate outlets/sumps.
- Overflow strategy: Always plan a safe overflow path to prevent back-up and internal ingress.
- Valleys: Size to flow, protect against scouring at outlets, and avoid pinched laps.
9) Heritage & conservation considerations
On listed buildings, respect original detailing while meeting modern performance expectations. Increased sheet thickness (Code 6–7) may be justified by span, exposure or access limitations. However, avoid “over-arming” small flashings. Use reversible methods where required and document interventions.
Coordinate with conservation officers and record before/after with photographs and drawings. Heritage doesn’t excuse ponding or poor falls.
10) A simple 6-step lead code selection workflow
- Identify the detail. Flashing, bay, roll, gutter, valley, dormer, etc.
- Measure span & length. Note width, intended centres, and panel length.
- Assess exposure. Shelter/coastal/upland? Increase code or reduce centres accordingly.
- Set drainage strategy. Falls, drips, outlets and safe overflow route.
- Choose provisional code. Use tables above; Code 4 for many flashings, Code 5–6 for bays/gutters.
- Check fixings & laps. Verify clip/strap spacing, lap sizes and chase details. Adjust as needed.
11) Worked examples
Example A: Pitched roof step flashing to brick abutment
Detail: Slate roof abutting brickwork at 30° pitch. Moderate exposure. Traditional stepped flashing with soakers.
- Selection: Soakers Code 3–4; step flashing Code 4.
- Reason: Code 4 provides enough stiffness while bossing neatly into joints. Soakers remain light and discrete.
- Checks: Upstand height, chase depth, compatible pointing material and clip spacing.
Example B: Parapet gutter on a town terrace
Detail: 12 m parapet gutter with outlets at 6 m centres; urban exposure, roof drains to internal downpipes.
- Selection: Code 5–6 sheets, bay widths ~600–700 mm with regular drips; increase to Code 6 if debris risk is high.
- Reason: Handles water loading, reduces fatigue risk, and limits ponding with drips and adequate falls.
- Checks: Overflow path, sump sizing, outlet protection and clip/strap spacing.
Example C: Dormer roof with hollow rolls
Detail: Lead-clad dormer in exposed setting; low slope; visible from street level.
- Selection: Code 5 for general dormer bays; Code 6 if spans are wide or falls shallow. Roll centres 450–600 mm.
- Reason: Balance of stiffness, movement control and aesthetic definition from roll caps.
- Checks: Neat roll ends, correct bossing at junctions, and unimpeded flow at drip edges.
12) Common defects & how good selection prevents them
- Fatigue cracks at drips: Often too-wide bays, inadequate falls, or under-spec’d code. Solution: reduce bay width and/or increase to Code 6; check falls.
- Nail pops & loose flashings: Over-tight clips, thermal pinching, or too-stiff code for detail. Solution: correct clip spacing and allow sliding; consider Code 4 for flashings.
- Ponding & staining: Insufficient falls or blocked outlets. Solution: redesign drainage and add safe overflow; review bay centres.
- Mortar failure in chases: Movement not accommodated or incompatible pointing. Solution: correct chase depth and materials; coherent lead code selection with movement strategy.
13) On-site checklist (printable)
- Detail identified and measured (length × width) ✅
- Exposure class reviewed (coastal/upland/urban) ✅
- Falls, drips and outlets set out ✅
- Provisional code selected (3–8) with justification ✅
- Clip/strap spacing set to standard ✅
- Upstands, chases and lap lengths confirmed ✅
- Overflow path designed (gutters/valleys) ✅
- Condensation risk reviewed (build-up/underlay) ✅
- Photograph and record all junctions for handover ✅
14) Useful links & where to buy
Ready to act on your lead code selection? Use these resources:
