When the roof sheathing is less than what thickness, nails must penetrate through the sheathing?

Nails must penetrate through the roof sheathing when the thickness is less than 3/4 inch. This requirement ensures that there is sufficient grip and holding power for the roofing materials being installed. In roofing applications, if the sheathing is thinner, the risk of nail pull-out increases, which could lead to potential failure of the roof system under adverse conditions.

Using nails that penetrate through sheathing of adequate thickness helps to maintain the structural integrity of the roof, as it enhances the overall fastening strength, reducing the likelihood of wind uplift and other forms of mechanical failure. Thus, the correct threshold thickness for when this requirement applies is indeed 3/4 inch.