What should be considered for the fastener length in wood roofing?

The design thickness of roofing materials is the key factor in determining fastener length in wood roofing. Fasteners must penetrate deep enough into the roof structure to provide secure holding power and to ensure the roofing materials are properly anchored. This requires that the fasteners accommodate the total thickness of all materials being used, which includes any underlayment, insulation, and the roofing material itself.

When selecting fastener length, it's crucial to factor in this design thickness to prevent issues such as insufficient holding power or damage to underlying materials. If the fasteners are too short, they may not reach the structural elements of the roof adequately, potentially leading to failures. Conversely, if fasteners are excessively long, they could penetrate too deeply, risking damage to the underside of the roof or creating points of weakness where moisture can enter.

Considering just the thickness of the exterior sheathing, standard lengths, or installation speed would not provide sufficient assurance of a secure installation, since they do not account for the cumulative thickness of all components that the fasteners must engage.