Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
CP 00143 — Sheet Roof and Wall Coverings (CP 143)
Code of Practice for Sheet Roof and Wall Coverings (CP 143, 2007 confirmed edition)
🏗️ CP 143 is the British Standards Institution (BSI) Code of Practice for Sheet Roof and Wall Coverings series, part of the early British “Code of Practice” system, confirmed as current in 2007. The series provides a complete set of engineering requirements — materials, design considerations, laying practice, and inspection and maintenance — for different metal sheet roof and wall covering systems, and has long been an important technical reference for metal roofing work in the UK and Commonwealth countries. This article presents the series as a whole: its structure and the technical requirements of its main parts.
💡 A metal roof looks simple, but success depends on the details: laps, fixings, flashings, eaves, and drainage. CP 143 systematically specifies these critical areas, providing the technical assurance for weathertight, durable, and attractive metal roofing.
1. Series Overview 📌
The CP 143 series is structured by covering material. The four parts in this batch (2007 confirmed editions) are as follows:
| Part | Edition | Subject | Main Content |
|---|---|---|---|
| CP 143-5 | 1964 (2007) | Part 5: Corrugated plastic sheet | Materials and laying requirements for corrugated (e.g. PVC) sheet roof and wall coverings (scan version; written from public domain knowledge). |
| CP 143-10 | 1973 (2007) | Part 10: Galvanized corrugated steel (metric) | Material, profile dimensions, design considerations, laying, inspection and maintenance for galvanized corrugated steel sheets. |
| CP 143-12 | 1970 (2007) | Part 12: Copper (metric) | Copper sheet roofing: standing seams, rolls, welt details, laying practice and inspection. |
| CP 143-15 | 1973 (2007) | Part 15: Aluminium (metric) | Aluminium sheet roofing: standing seam and batten roll, long strip systems, clips and laying practice. |
⚠️ Part 5 (CP 143-5:1964) is a scan-only file in the source material; its content is summarised from public domain knowledge. Always refer to the official BSI published version.
2. Materials and Construction Requirements 🧱
Galvanized corrugated steel (Part 10) specifies the material, zinc coating mass, and profile dimensions of galvanized sheets. Typical corrugation profiles are 76.2 mm and 127 mm pitch; the standard gives effective cover width per sheet, approximate weight (including laps), and mechanical properties, from which the purlin spacing limits are determined for safe stress and deflection. Sheets are protected by galvanizing and are used with sealing material, flashings, galvanized rainwater goods, and walkways.
Copper (Part 12) and Aluminium (Part 15) belong to thin sheet roofing systems, where the key technology is the joint form: copper uses standing seams and rolls; aluminium uses traditional standing seam and batten roll systems plus the long strip system. Thin sheets expand and contract significantly, so thermal movement must be released through expansion joints and expansion clips to prevent buckling and leakage.
| Covering Material | Typical Joint/System | Key Accessories | Durability Notes |
|---|---|---|---|
| Galvanized corrugated steel | Side lap, end lap, crest fixing | Flashings, sealing compound, rainwater pipe, walkway | Zinc coating; needs periodic painting |
| Copper sheet | Standing seam, roll, single/double lock welt | Roofing felt, copper nails, solder | Patina self-protection; long life |
| Aluminium sheet | Standing seam, batten roll, long strip | Felt, timber battens, clips (plain/expansion) | Light and corrosion-resistant; watch galvanic corrosion |
3. Design Consideration Points 🔧
- Durability: choose sheet and coating per material corrosion characteristics and environmental exposure, and consider repainting cycles.
- Weathertightness: design lap direction, pitch, and details to prevent water ingress.
- Thermal and condensation: provide insulation and underlay to control condensation and avoid moisture build-up.
- Fire: assess external fire exposure performance per relevant requirements such as BS 476.
- Loads and support: determine purlin spacing from sheet strength and deflection limits, considering wind suction, snow, and maintenance loads.
- Roof accessories: pipes passing through the roof, ventilators, rooflights, and gutters and rainwater pipes must be provided for and flashed/sealed.
- Lightning protection: metal roofs must be earthed and bonded per lightning protection requirements.
4. Laying Practice, Inspection and Maintenance 🛠️
Construction emphasises safety (ladders, scaffolding, hoists), sheet storage and handling protection (against scratching and distortion), setting out, and fixing sequence. For copper and aluminium thin sheets, lay the underlay first, then position sheets and form joints in sequence, completing details at eaves, ridges, gutters, and parapets. Inspection covers material acceptance, substructure/underlay checks, work-in-progress checks, and final inspection; maintenance focuses on periodic inspection and painting (especially galvanized sheets), clearing drainage, and checking joints and flashing seals.
🚨 The biggest risks for thin metal roofing are “joint cracking from thermal expansion” and “galvanic corrosion from dissimilar metal contact”. Always set expansion joints, use sliding clips, and isolate aluminium from copper, steel, and other dissimilar metals.
5. Frequently Asked Questions ❓
❓ Q: How does CP 143 relate to current BS EN metal roofing standards?
A: CP 143 is an early code of practice; parts of it have been absorbed into or superseded by later BS/EN sheet and roofing standards. As a long-standing engineering practice reference, its details and construction methods remain valuable; new work should prioritise current BS/EN standards.
A: CP 143 is an early code of practice; parts of it have been absorbed into or superseded by later BS/EN sheet and roofing standards. As a long-standing engineering practice reference, its details and construction methods remain valuable; new work should prioritise current BS/EN standards.
❓ Q: How are the pitch and thickness of galvanized corrugated steel chosen?
A: The standard gives effective cover width, approximate weight, and mechanical properties by pitch (e.g., 76.2 mm, 127 mm), and derives purlin spacing limits. Selection combines loads (wind, snow, maintenance) with deflection limits.
A: The standard gives effective cover width, approximate weight, and mechanical properties by pitch (e.g., 76.2 mm, 127 mm), and derives purlin spacing limits. Selection combines loads (wind, snow, maintenance) with deflection limits.
❓ Q: Why do copper and aluminium sheet roofs need expansion joints?
A: Metals expand and contract significantly; if strips are fully fixed at both ends, temperature changes create large stresses, causing buckling or joint cracking. Expansion joints and sliding clips allow free movement, ensuring weathertightness.
A: Metals expand and contract significantly; if strips are fully fixed at both ends, temperature changes create large stresses, causing buckling or joint cracking. Expansion joints and sliding clips allow free movement, ensuring weathertightness.
❓ Q: What are the key daily maintenance points for a metal roof?
A: Periodically inspect joints, flashings, and sealant ageing; clear gutters and rainwater pipes to prevent blockage; check for loose fixings; and repaint per the coating life cycle.
A: Periodically inspect joints, flashings, and sealant ageing; clear gutters and rainwater pipes to prevent blockage; check for loose fixings; and repaint per the coating life cycle.