What is Purlin?

Definition of Purlin in Construction
A purlin is a small structural member that spans between larger structural members.

In a metal structure, the purlins can be in the walls or ceilings, and are used to attach the exterior skin of the metal structure, the interior finishes, or support the wall and ceiling installation. Normally the purlin spacing is designated as an on center spacing and the installation consistency is important to siders, roofers, etc. These applications, use the purlin locations as supports for their materials.