Steel: Steel is the most common and least expensive metal. It can be an excellent choice for roofing, because it is very strong and durable.
Galvanized steel has a fair level of protection against the natural elements so that it will not rust under normal environmental conditions. Two methods are used to galvanize steel. G-90 steel has been hot dip galvanized with a coating of zinc.
Galvalume is an alternative coating that offers a higher level of protection, which is composed of a blend of aluminum and zinc. Both coatings can prevent corrosion and rust very effectively, and can usually enable properly-installed steel roofs to last for upwards of 50 years.
G-90 steel is created by dipping sheets or coils of steel in liquid zinc, so that a protective layer of 0.9 ounces or more of zinc is formed. This layer can prevent the steel from becoming corroded or oxidized, which creates what is generally known as rust. G-90 steel is very well protected, even when it is cut or scratched.
Galvalume steel is a better option for roofs that are exposed to a somewhat salty area such as the marine environment. Although G-90 steel provides excellent protection against the elements, which is also enhanced by a cool Kynar coat paint finish, it is not as effectively protected against the corroding properties of salty air as galvalume steel.