Exterior sheathing (glass mat product or wood) requires an exterior fastener. A zinc-plated screw is for interior use only… (Typically Shinny fasteners)
Gypsum board sheathing damage MUST be repaired (replaced) STUD to STUD prior to any roofing or air /vapor barrier being installed
The installation of exterior sheathing is critical; many contractors rely on the proper installation of the sheathing for their installations. Overlapping corners are critical for proper installation.
Glass mat sheathing is mold-resistant; however, this does not make it mold-proof. Generally, this type of material cannot be immersed in water, subjected to constant condensation, or installed in a way that it will wick moisture. Any material, including glass & aluminum will support mold if the conditions are right.