What is the maximum distance purlins can be unsupported?

The maximum distance that purlins can be unsupported is determined by the structural requirements for load-bearing capacity and stability. In residential construction, purlins are typically used in roofing systems to provide support for roofing materials and to carry loads to the structural framework. A distance of 4 feet is commonly specified for purlin spacing as it helps to ensure that the purlins can adequately support the weight of the roof and any additional loads, such as snow or wind.

This 4-foot limit allows for sufficient structural integrity while also facilitating ease of construction and reducing the risk of sagging or failure of the roofing system. Purlins installed beyond this distance may experience excessive flexural stress, which could lead to structural issues. It's crucial for inspectors to verify the spacing to comply with building codes and ensure safety and performance in residential structures.