What does a purlin do in a structural framework?

A purlin plays a crucial role in a structural framework by transferring loads from the roof to the walls. It is typically a horizontal member situated between the rafters and helps distribute the weight of the roof evenly across the walls of the structure. This load transfer is essential because it ensures the stability and integrity of the building, particularly when faced with environmental factors like wind and snow loads.

In contrast, the other options discuss functions that do not pertain to the primary role of a purlin. Connecting two rafters is more typically the function of a rafter tie or collar tie. Supporting insulation is a task related to the overall roofing system but is not specific to the role of a purlin, which primarily focuses on load management. Stabilizing the foundation is a responsibility of the foundation itself and structural elements that directly interact with it, rather than the roof structure where purlins are located. Thus, the definition and function of a purlin distinctly underline its importance in structural stability and load distribution.