Purlins must be supported by braces installed at what minimum slope?

The requirement for braces to support purlins at a minimum slope of 90 degrees from the horizontal is grounded in structural integrity and load distribution principles. When braces are installed vertically, or at a 90-degree angle, they effectively transfer loads directly downward and provide the maximum level of support to the purlins. This vertical alignment allows for optimal weight distribution and enhances the overall stability of the structure.

In contrast, using slopes less than 90 degrees can lead to less effective load transfer and can compromise the structural performance of the purlins. For example, at angles like 45 degrees or 30 degrees, the bracing system might not provide sufficient vertical support, particularly under heavy loads or adverse weather conditions. This could result in the purlins experiencing unnecessary stress or even failure, which could compromise the entire roofing system's safety and durability.

Thus, the specification for braces to be installed at a minimum slope of 90 degrees ensures that purlins are adequately supported, maintaining the structural integrity of the roof assembly.