Purlins vs Girts

Purlins vs Girts

Purlins and Girts are both use in construction.  They are typically dimensional lumber 2x4s, 2x6s and in the case of girts 2x8s.  In the pole barn framed picture, purlins are the horizontal boards going across the roof trusses, and the girts are the horizontal boards going across the vertical poles in the walls of the building.  In the picture, and often in practice, the girts are 2x6s that lay flat on the posts, and the purlins are 2x4 stood on edge.  Note that the spacing between the purlins may significantly differ from the spacing between the girts.

Girts are differ from purlins in that girts are primarily used to support the exterior cladding of a building, such as siding or sheeting. Girts help to stabilize the cladding and distribute wind and other lateral loads to the building's main structural frame.  Purlins, on the other hand, are used to support the roof covering and transfer loads to the primary roof framing system, such as rafters or trusses. They help to distribute the weight of the roof covering evenly across the roof structure and provide stiffness to the roof system. Furthermore, girts are typically installed horizontally between the vertical structural members, such as columns or posts, on the exterior walls of a building. Purlins are installed horizontally parallel to the slope of the roof and are typically spaced apart at regular intervals along the length of the roof. Girts provide support for the exterior cladding and help to transfer wind and other lateral loads to the building's main structural frame. Girts also help to stiffen the walls of the building. Purlins provide support for the roof covering and help to distribute the weight of the roof evenly across the roof structure. They also help to stiffen the roof system and resist wind uplift.