What is the Difference Between Galvanized and Galvalume Roofing?

When completing a project with corrugated sheet should you go with a galvanized or Galvalume metal roof?

The answer lies in the difference between the two. Traditional galvanized metal roofing is a corrugated sheet of carbon steel with a galvanized coating. The coating is created by dipping the straight sheet in hot molten zinc. The zinc ions bond with iron molecules in the steel to create a shiny, rust-resistant finish on its surface. This process is called galvanization.

After the coating hardens, the sheet is put through a cold forming corrugation process, which bends the sheet into parallel linear patterns. These “corrugations” give the sheet more strength and stability when it is installed as a roof.

The patented Galvalume process invented by Bethlehem Steel in 1972 is similar to galvanization, but also adds aluminum and silicon to the zinc. As the coating dries, patches of aluminum and zinc molecules coalesce into a pattern across the surface of the sheet. The aluminum areas provide corrosion resistance and the zinc provides galvanization protection. The small amount of silicon helps the coating adhere to the underlying metal, even when it is being cut or rolled into the corrugated shape.

So which one is better for a roof? There are pros and cons to each type.

The extra corrosion resistance of Galvalume means that scratches, bends, or cut edges won’t rust so quickly, and it also makes a better choice in rainy climates and in salt air.

Paint does not adhere as well to Galvalume, so the aesthetics may not be as good. Also, Galvalume costs more than galvanized metal roofing – but the fact that a Galvalume metal roof will last up to twice as long as a galvanized roof of the same thickness could make up the difference. For these reasons, Galvalume metal roofs are much more popular.

Typically, galvanized sheet roofs are used mainly for agricultural buildings, where rust is less of an issue and costs must be kept low. Galvanized metal roofs may also be used by architects looking for a traditional, rusted appearance in a new building.

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