In most cases when someone refers to galvanized metal roofing they are specifically referring to an inner metal layer of iron and carbon alloy steel that has been dipped in a hot zinc bath and is now coated with a thin layer of the material.
Galvanized zinc roof.
Galvanized g90 g90 is not a galvanizing specification.
Galvanized and galvalume steel will forgo that aging for a couple of decades.
When steel is galvanized it is really just adding a protective layer of zinc to dteel base to protect it from oxidation as steel is naturally corrosive or will rust when exposed to salt water or moist environment over a long period of time.
Many metal roofs are made out of galvanized metal which is a type of metal that has been covered with hot zinc in order to protect it from the weather.
It is a coating thickness designation in the galvanizing specification astm a653.
However paint on metal roofs often peels or rusts in which case it is time to repaint it.
Before the introduction of galvalume to the metal roofing industry in the late 20th century using galvanized sheet and coil was a common practice.