Purlins are secondary structural steel members that span between roof trusses or rafters to support roof sheeting in industrial buildings, factory sheds, and warehouses. In India, C purlins and Z purlins are the two most common cold-formed steel sections used in industrial roofing systems. This guide covers purlin types, sizes, IS standards, and selection criteria.
What Are Purlins in Steel Construction?
A purlin is a horizontal structural member running along the length of a building, spanning between roof trusses or rafters at 1.2–1.8m centres. Purlins carry the self-weight of the roof sheeting, wind uplift loads, and any imposed loads (maintenance loads, solar panels) and transfer them to the primary structural frame. Without purlins, roofing sheets would have no support between trusses.
C Purlin vs Z Purlin — What’s the Difference?
| Feature | C Purlin (C Section) | Z Purlin (Z Section) |
|---|---|---|
| Cross-section shape | C / channel shape | Z / offset flange shape |
| Lapping | Cannot be lapped (flanges face same direction) | Can be lapped at supports (flanges interlock) |
| Continuity | Simply supported — one span at a time | Continuous over supports via lapping — stronger |
| Structural efficiency | Lower — simply supported | Higher — continuous action, less steel per span |
| Typical span | Up to 6–7m | Up to 8–10m lapped, 6–7m unlapped |
| Cost | Slightly lower | Slightly higher but uses less material overall |
| Common use in India | Light industrial sheds, secondary structures | PEB buildings, large industrial sheds |
C Purlin Sizes — Standard Range in India
Standard C purlin sizes available in India (cold-formed to IS 811):
- C 100 × 50 × 2.0mm / 2.5mm
- C 150 × 65 × 2.0mm / 2.5mm / 3.0mm
- C 200 × 75 × 2.5mm / 3.0mm
- C 250 × 75 × 3.0mm / 3.15mm
- C 300 × 90 × 3.0mm / 3.15mm / 4.0mm
Z Purlin Sizes — Standard Range in India
Standard Z purlin sizes available in India (cold-formed to IS 811):
- Z 150 × 65 × 2.0mm / 2.5mm
- Z 200 × 75 × 2.5mm / 3.0mm
- Z 250 × 75 × 3.0mm / 3.15mm
- Z 300 × 90 × 3.0mm / 3.15mm / 4.0mm
- Z 350 × 100 × 4.0mm
Purlin Material and IS Standards
- IS 811:1987 — Specification for cold-formed light gauge structural steel sections (covers C and Z purlins).
- IS 801:1975 — Code of practice for use of cold-formed light gauge steel structural members in general building construction.
- IS 1079 — Hot-rolled steel strip/sheet used as base material for cold-formed purlins.
- Base material: Pre-galvanised steel (Galvalume or GI) or ungalvanised MS depending on corrosion exposure. Galvanised purlins are standard for most Indian industrial buildings.
Purlin Spacing for Industrial Sheds
Purlin spacing depends on the roof sheeting thickness and span capability, wind load zone (IS 875 Part 3), and imposed loads. Typical purlin spacing in Indian industrial buildings:
- Light industrial sheds (low wind zone): 1.5–2.0m centres with 0.47mm TCT sheeting.
- Standard industrial buildings: 1.2–1.5m centres with 0.50mm TCT sheeting.
- High wind zone / coastal areas: 1.0–1.2m centres with 0.60mm TCT or 0.70mm sheeting.
MS Purlin vs Cold-Formed Purlin
MS purlins (mild steel angles or channels — hot-rolled) were widely used in older Indian industrial buildings. They are heavier, require site drilling, and have lower structural efficiency than cold-formed C and Z purlins. Today, cold-formed C and Z purlins are the standard for new industrial shed construction because they are lighter, pre-drilled for sheeting screws, and structurally more efficient per kg of steel.
Purlin Supply and Fabrication — Suncorporation
Suncorporation Fabricators & Engineers supplies and installs C purlins, Z purlins, and MS purlins as part of complete industrial shed fabrication and erection contracts across India. Our purlin supply includes all standard sizes in galvanised and ungalvanised options, cut to length and despatched with the primary structure.
We serve projects in Hyderabad, Bengaluru, Chennai, Mumbai, Delhi NCR, and Kolkata. Contact us for a purlin supply and erection quotation.