A purlin is a secondary structural member that connects the primary steel frames of rafters and columns and also to support Roofing and wall cladding Sheets. The purlin transfers load from the roof and wall cladding to the primary steel rafters and columns. Purlins are used to provide restraint to the primary steel frame members. Purlin and girts are Cold formed steel members having an yield strength of 300 MPa or more and can be efficient on weight basis and also cost effective compared to mill rolled heavier steel angles and channel sections.

The principal advantage of cold roll-forming, compared with other methods of fabrication, is the high production capacity achieved and is essentially uniform in cross section and can be manufactured to very close dimensional tolerances. Purlin, commonly termed as Z and C Sections, are defined by a central vertical web joined to horizontal flanges at either end. Additional lips are included to support the flanges. It is available in HR and GI grades and also in different thicknesses and depth depending on design of the building. Purlin can be supplied in customized length with pre-punched holes as per architectural designs.