#Proper Leadwork: Hollow Rolls & Wood Rolls—Geometry, Centres & Fixing Patterns
Elegant, resilient lead roofs often rely on lead hollow roll caps (with timber cores or formed hollows) to control movement and create the classic rhythm of traditional sheet roofing. This guide sets out geometry, roll centres, fixing patterns, code selection (typically Code 5–6), and the small workmanship choices that prevent fatigue, rippling and leaks—so your rolled work looks as good in year 30 as it did on day one.
Shop Wood Rolls & Timber Cores
Clips, Nails & Straps
Lead Underlay & Support
The Lead Lads: Services & Prices
Lead Lads Standards Hub
GNR Roofing: Leadwork Authority
Regulatory Standards (BS 6915)
Part 5 of our “Proper Leadwork: Technical Series”. Pair with Part 1 (codes) and Part 2 (movement) for full context.
1) Why hollow rolls & wood rolls?
Rolls subdivide wide areas into smaller bays, letting sheets expand and contract without concentrating stress. A lead hollow roll also stiffens the assembly and provides a cap that sheds water. Timber-cored “wood rolls” achieve the same movement control with a tactile, heritage aesthetic.
- Movement control: Rolls break sheets into bays, limiting creep and fatigue.
- Drainage: Rolls pair with drips to set a clear water path.
- Aesthetics: Even, rhythmic roll lines signal quality #proper leadwork.
2) Code selection & sheet layout
For rolled work, Code 5 is common; Code 6 is used for wider spans or severe exposure. Code choice and bay width go hand-in-hand: heavier code allows slightly wider bays, but smaller bays with correct falls nearly always outperform simply “going heavier.”
| Application | Typical Code | Indicative Bay Width | Notes |
|---|---|---|---|
| Dormer roofs | 5–6 | 450–600 mm | Visible façades benefit from tighter centres |
| Low-slope bays | 5–7 | 500–750 mm | Increase falls and use regular drips |
| Parapet/box gutters | 5–7 | Up to ~600–800 mm | Use straps; protect outlets and add sumps |
3) Roll centres by exposure & span
Set roll centres early in design. Consider wind exposure, roof geometry and visibility. In severe exposure (coastal/upland), tighten centres. Consistency is king—uneven spacing telegraphs across the roof.
| Exposure | Recommended Centres | Comments |
|---|---|---|
| Sheltered/urban | 550–650 mm | Common for dormers and small bays |
| Normal | 500–600 mm | Default range for most roofs |
| Severe/coastal | 450–550 mm | Tighten spacing; consider Code 6 |
Align roll centres with window axes and façade rhythms where possible for visual harmony.
4) Timber cores vs formed hollow rolls
You can create a lead hollow roll in two main ways: by forming the lead over a timber core (wood roll), or by creating a self-supporting hollow without a core (more advanced bossing/welding). Timber cores are predictable and fast; formed hollows reduce potential abrasion points and can be lighter.
Timber (wood) roll cores
- Consistent diameter and straightness.
- Simple, repeatable installation—great for teams.
- Ensure cores are smooth, sealed and securely fixed to deck.
Formed hollow rolls
- Reduced point contacts; potentially less abrasion.
- Requires higher bossing skill; consistent radii essential.
- Use templates/jigs to control diameter along the run.
Whichever route you choose, keep radii and centres consistent. Irregular cores or wavy hollows lead to stress concentrations and visible defects.
5) Fixing patterns: clips, straps & nailing
Fixings restrain uplift without pinching thermal movement. Leave laps free of nails. Use copper or stainless for durability. Straps are essential on gutters and broad cappings; clips control sheets at roll edges and drips.
| Detail | Fixings | Spacing | Notes |
|---|---|---|---|
| Roll edges | Clips (Cu/SS) | 300–450 mm | Even spacing; allow longitudinal slide |
| Drips | Clips | 300–400 mm | Never fix through the lap |
| Parapet/box gutters | Straps + clips | 300–400 mm | Increase in severe exposure |
| Verges/cappings | Clips + straps | 300–400 mm | Watch local wind uplift |
Over-tight fixings cause ripples and creep. The sheet must be able to slide along its length.
6) Drips, welts & end closures
Rolls and drips work together. Drips prevent water dwelling; welts stiffen edges and resist capillary action. End closures at ridges, verges and abutments must not trap water or block movement.
- Drips: Provide at sensible centres on low slopes; form smooth radii—no sharp creases.
- Welts: Welt long edges in exposed sites to stiffen the seam and limit capillary tracking.
- End closures: At roll ends, form caps with gentle radii; avoid “pinched” corners.
- Abutments: Turn rolls neatly into flashings; keep chase depths consistent.
7) Decks, underlay & friction control
Smooth, continuous decking prevents abrasion and telegraphing. Purpose-made underlay reduces friction and noise so sheets can move quietly with temperature swings.
- Deck: Flat, clean, free of proud fixings or splinters; treat knots or irregularities.
- Underlay: Low-friction lead underlay between sheet and deck, continuous under rolls.
- Build-up: Check condensation strategy (warm vs cold roof) and VCL position.
8) Verges, abutments & penetrations
Interfaces are where good rolled work shines. Keep edges crisp, movement paths clear and water guided away from traps.
- Verges: Maintain roll rhythm to the edge; finish with neat returns or verge trims.
- Abutments: Integrate rolls under step/cover flashings with consistent laps.
- Penetrations: Use saddles or secret gutters to steer water; avoid tight corners.
Coordinate with window heads, cornices and parapets so roll centres land symmetrically.
9) 8-step workflow for rolled lead
- Choose code (5–6 typical) for span/exposure.
- Set centres (450–650 mm based on exposure/visibility).
- Design falls and overflow path; place drips at sensible intervals.
- Select core type (timber vs hollow) and confirm radius/diameter.
- Specify fixings (clips/straps @ 300–450 mm); keep laps free of nails.
- Prepare deck & underlay (smooth, continuous, low-friction).
- Form rolls with consistent radii; soften ends; welt long edges in exposure.
- QA lines, spacings, photos and handover record.
10) Worked examples
Example A: Heritage dormer roof (urban, visible)
Goal: Crisp façade lines with long service life.
- Code: 5 throughout; consider 6 if spans approach 600 mm.
- Centres: 500–550 mm, aligned to window symmetry.
- Core: Timber wood rolls for repeatable radius.
- Fixings: Clips at 300–400 mm; no pinning through laps.
- Edges: Welt long edges; soften roll ends; neat verge returns.
Example B: Low-slope bay with debris risk (trees nearby)
Risk: Ponding and abrasion from debris.
- Code: 6; drips at closer intervals.
- Centres: 450–500 mm to limit sheet width.
- Core: Formed hollow roll to reduce contact points.
- Drainage: ≥1:80 fall; protected outlets; defined overflow.
Example C: Parapet gutter with roll-capped cover
Need: Stiffness and tidy cap against wind uplift.
- Code: 6; straps at 300–400 mm.
- Core: Timber roll; check fixings into parapet framing.
- Edges: Welt and clip; avoid hard stops at corners.
11) Common defects & prevention
- Fatigue at roll ends: Sharp folds, no radius. Fix: Re-form with gentle radius; relieve stress.
- Rippled bays: Centres too wide; clips too tight. Fix: Tighten centres; reset clips to allow slide.
- Ponding/staining: No drips or flat falls. Fix: Add drips; re-set falls; clear overflow.
- Abrasion/telegraphing: Rough deck or no underlay. Fix: Smooth deck; install underlay.
- Capillary ingress: Unwelted long edges in exposure. Fix: Add welts; review laps.
12) On-site checklist (printable)
- Code 5–6 selected based on span/exposure ✅
- Roll centres set (450–650 mm) & aligned visually ✅
- Falls designed; drips located; overflow path set ✅
- Wood rolls or hollow form chosen; radii consistent ✅
- Deck smooth; low-friction underlay installed ✅
- Clips/straps @ 300–450 mm; laps free of nails ✅
- End closures with soft radii; welts on long edges (exposure) ✅
- QA photos of lines, spacings, ends & outlets ✅
13) Useful links & where to buy
