What Are C and Z Purlins?

Purlins are horizontal structural members used to support roof decking, wall cladding, or sheeting in steel-framed buildings. Unlike primary structural beams, purlins span between rafters or portal frames and directly carry the load of roofing panels, insulation, and environmental loads such as wind and snow.

The most widely used purlin profiles in the industry today are the C purlin (also called C-section or lipped channel) and the Z purlin (also called Z-section or zed purlin). Both are manufactured through a cold roll forming process, which produces precise, high-strength cross-sections from flat steel coil — without the need for heat or heavy presses.

C Purlin — The Symmetrical Channel

The C purlin features a web (vertical back), two flanges extending in the same direction, and short return lips at the flange ends. Its symmetrical profile makes it straightforward to install in single-span configurations and is commonly used for wall girts, secondary framing, mezzanine supports, and short-bay roof purlins.

Z Purlin — The Overlapping Performer

The Z purlin has a web and two flanges extending in opposite directions, forming a distinctive Z-shaped cross-section. This geometry allows adjacent purlins to be overlapped at supports — effectively creating a continuous beam that dramatically improves load-carrying capacity over multi-span roofs. Z purlins dominate in large industrial, agricultural, and commercial steel buildings where span efficiency is critical.

Raw Materials: Steel Coil Selection and Properties

C and Z purlins are cold-formed from flat steel coil (strip steel), which is fed continuously into a roll forming line. The choice of coil material directly affects the structural performance, corrosion resistance, and service life of the finished purlin.

Primary Material Types

Key Material Parameters

The growing adoption of high-strength steels (G550, S550) in purlin production allows manufacturers to achieve equivalent structural performance with 15–25% less material weight, reducing both raw material cost and freight. However, higher-strength coils demand tighter roll forming tolerances and more rigid machine frames to prevent springback and dimensional drift.

Standard Purlin Specifications and Dimensions

The dimensional designation of a C or Z purlin typically follows the pattern: Profile Type – Web Height × Flange Width × Lip Length × Thickness.

Purlin lengths are typically cut to order in the range of 6–12 m, though modern roll forming lines with flying cut-off saws can produce custom lengths without stopping the forming process — a key efficiency advantage in high-volume production environments.

The Manufacturing Process: Cold Roll Forming

Cold roll forming is a continuous bending process in which a flat steel strip is progressively shaped through a series of paired roll stations — each station incrementally forming the profile closer to its final cross-section. Unlike press-braking, roll forming is a continuous, high-speed process ideally suited to the long, constant cross-sections of purlins.

A complete purlin roll forming line typically comprises: an uncoiler (decoiler) to hold and release the steel coil; a straightening and feeding unit to correct coil curvature and set material tension; the roll forming mill with multiple forming stations; a servo-hydraulic flying cut-off press or post-cut shear to cut sections to length at speed; and a stacking and bundling system for finished sections.

The number of forming stations varies by profile complexity. C and Z purlins typically require 12 to 18 forming passes to achieve dimensional accuracy, tight corner radii, and consistent straightness over long lengths.

Purlin Roll Forming Machines: What the Industry Uses

The global market for purlin forming equipment centres on three machine types, each addressing different production requirements.

C Purlin Machine

A dedicated C purlin roll forming machine is configured with fixed tooling optimised for C-section geometry. It delivers consistent, high-speed output for single-profile production environments. Production speeds typically range from 25 to 60 m/min.

Z Purlin Machine

The Z purlin roll forming machine incorporates the asymmetric tooling geometry required for the Z-section profile. Because Z purlins are often produced as mirrored pairs, some machines incorporate adjustable or reversible roll station configurations.

CZ Interchangeable Purlin Machine

The CZ interchangeable purlin machine is the industry’s most versatile solution. Through an adjustable roll-station mechanism — typically involving movable shafts, interchangeable cassettes, or motorised width adjustment — a single machine can produce both C and Z profiles across a range of sizes.

Choosing the Right Machine: Key Considerations