Which of these fastening methods does NRCA recommend when installing a slate roof?

The recommended fastening method for installing a slate roof involves ensuring that the nail head is in contact with the slate without driving the nail through it. This approach is significant because driving a nail through the slate can create a potential point of leakage and can weaken the slate over time. Touching the nail head to the slate allows for proper securing of the slate while maintaining its integrity and ensuring that water does not penetrate through openings that could lead to roofing problems.

Using adhesive under each slate, while it may sound appealing for additional security, is not a typically recommended practice as it can complicate future repairs and maintenance. Installing slate without any fasteners is impractical, as slates need to be secured to withstand weather elements. Therefore, contacting the nail head to the slate is the most balanced approach, providing both stability and maintaining the slate's structural soundness.