If you live near the coast, your metal roof is going to be affected by corrosion caused by the sea air. Fine particles of sea salt, usually formed by the evaporation of sea spray, creates a salt haze – and it is this haze which corrodes your roofing screws, causing them to breakdown. Once this process begins the performance is greatly compromised over their lifetime.
Besides being caused by salt air, corrosion of roofing screws can also result from acids carried through the air from industry and chemical sprays, U.V. from the sun, or humidity in tropical and damp areas.