Particularly with older buildings, the soffit overhangs of the roof may result in roof decking that is exposed on its underside.
Most metal roofing manufacturers recommend that the fasteners used to install their products be of adequate length to fully penetrate the roof decking and emerge from the underside. When exposed soffits exist, this could mean that fasteners from the metal roofing would be visible form the underside of the roof decking.
This problem should be recognized before roof installation begins. The best solution in most cases would be to install the roofing in these areas only using screws of a length that will not quite fully penetrate the decking. The screws must be of compatible metal to avoid electrolysis (see Technical Bulletin #42 for more information on Electrolysis). Screws are used rather than nails due to their superior pull-out resistance. Ensure that all applicable building codes are still met by the fasteners that are used.