What is a "purlin" in roof construction?

In roof construction, a purlin is crucial as it plays a significant role in providing horizontal support for the roof decking or sheathing. Purlins are installed perpendicular to the rafters and are typically used in post-and-beam structures. By supporting the roof covering, they help distribute the loads from the roof materials and any additional weight, such as snow or maintenance activities, directly to the structural framework. This ensures stability and integrity in the building’s roof system.

Having a functional understanding of a purlin is essential for a building inspector, as it enables proper assessment of a roof's structural integrity and compliance with building codes. Recognizing its role distinguishes it from vertical support beams, which serve a different function, or components related to insulation or roofing materials, which address other aspects of construction and energy efficiency.