What is the minimum permissible thickness for structural roof sheathing without edge support, having a live load of 30 psf and a total load of 40 psf?

The correct choice is based on structural standards set for roof sheathing materials, particularly when considering the loads involved. In this case, the minimum thickness of roof sheathing is determined by its ability to safely support the specified live load and total load without the benefit of edge support.

For structural applications, thickness not only ensures structural integrity but also considers factors such as span distances and type of material used. In this scenario, with a live load of 30 pounds per square foot (psf) and a total load of 40 psf, a thickness of 5/8 inch meets the necessary requirements for deflection and strength under these specified conditions.

Utilizing materials that adhere to established building codes ensures they are capable of handling the anticipated loads. In general, as loads increase, so does the need for thicker materials to prevent issues such as sheathing failure or excessive deflection, which can lead to structural problems over time. Thus, if no edge support is available, opting for 5/8 inch sheathing provides a margin of safety that is crucial for long-term performance and compliance with safety standards.