Is a horizontal beam or bar used for structural support in structures, most often below the roof. Purlins are supported either by the building’s rafters or its walls. These are most commonly used in metal buildings, but in wood-frame structures, these also replace closely packed rafters. A roof’s purlins support the roof Deck’s weight.

There are many types of purlins and are divided into groups depending on the material they are made of and the form of their shape. Different purlins are used for multiple uses including a structural wall or floor support. Purlin is necessary as there is no frame for the sheeting on the roof to rest on without it, thereby making purlins important to the roof structure.