What's the difference between a galvanized metal roof and a galvalume metal roof? In this episode, Jordan does a deep dive into the metallurgy behind these two finishes and explains the differences and similarities between them.
Long story short, a zinc galvanized metal roof protects the steel primarily by creating a zinc carbonate barrier between the steel and the corrosive environment. The zinc and steel also set up a galvanic cell which can cathodically protect bare steel up to about 0.125" away from the zinc coating.
Galvalume is 55% aluminum and 45% zinc and also primarily protects the underlying steel by creating a barrier coating. Galvalume also cathodically protects the steel, but because the galvanic potential is smaller between aluminum and steel than zinc and steel, it is not quite as effective. However, the oxide layer that is formed on the surface of galvalum is very tenacious and will not errode away as quickly as the zinc carbonate in the zinc/steel system.
Both roofing materials will give long lasting performance, but galvalum should have the longevity edge in normal applications.
Be careful to get a single lot run in both of these materials, as there will be color variations from lot to lot. If you are looking to have a very consistent color across a large roof, a painted metal roof will have more consistency in color from panel to panel and from lot to lot.
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