In this paragraph on Metal roofing instalation. "Two types of methods are commonly used to secure the panels to the roof sheathing. Hidden fasteners are secured to the raised portion of each panel, and subsequently covered by the next adjoining panel during installation. The second (and less costly) method utilizes exposed fasteners that are driven through each metal panel into the roof sheathing"
For the Hidden fasteners are they attached via screw / nail, or crimped into the next sheet when layed. A contractor indicated to us that installation is via a bonded element and then the pieces are crimped together? That does not seem workable but looking for comment.