ISSUE
Metal roofing panels are available in a variety of metals including steel, aluminum, copper, and zinc. While exotic steels such as stainless are sometimes used, the steels more commonly used in roofing are galvanized and galvalume. In considering a metal roof, it is important to understand the differences between these two types of steel.
ANALYSIS
Galvanized steel is carbon steel with a metallic coating of primarily zinc on its surface. Galvalume is carbon steel with a metallic coating or primarily aluminum on its surface. There is no problem with electrolysis between dissimilar metals because the metallic coating is a continuous coating with no ability for a catalyst to get between it and the carbon steel to prompt corrosion. With both galvanized and galvalume, various thicknesses of the metallic coatings are available. Galvanized is commonly G90 grade while galvalume is commonly AZ55 grade. One generally accepted attribute of galvalume is that the aluminum metallic coating provides greater corrosion resistance than does the zinc coating of galvanized. However, for metal roof profiles which have substantial forming and tight bends in the metal, the zinc of galvanized can have a better “bridging” effect to create superior corrosion resistance over the tight folds and bends.
