Hidden roof fasteners are also called concealed fasteners. They are primarily used for a metal roofing system, both commercially and residentially.

The hidden fasteners are under the metal roofing, making the screws not visible. A clip that hooks over a leg of the metal roofing panel properly secures the panel to the building.

This is also called a standing seam metal roof. There are two types of these: mechanically seamed standing seam and snap lock standing seam. The metal roofing panels for the mechanically seamed standing seams are put beside each other. Then the panels are locked together with a seamer mechanically bending them over the tops of each panel. The snap lock standing seam is the result of snapping the side of the metal roofing panel to the one beside it. This causes them to hook together and raise the seam.

These hidden roof fasteners are never exposed to the natural elements, such as rain, snow, hail, and sleet. They are protected by the roof itself. Because of this, the fasteners will last just as long as the roof and require less maintenance from the building owner. This saves time and money that possible leaks cause by other fasteners could create. However, these fasteners can be quiet expensive, but they last significantly longer than the exposed roof fasteners.

Sources:
http://www.mbci.com/products/roof/concealed-fastening-roof-systems/
http://mas-mistral.com/2015/08/04/metal-roof-fasteners-should-you-use-exposed-or-hidden-fasteners/
http://www.exteriorproinc.com/blog/choose-the-right-metal-roofing-for-your-home-or-business