Q: Will A Metal Roof Rust? A: Union�s premium roofing products utilize high strength Metal Construction Association (MCA) certified steel that�s protected by an aluminum, zinc, and silicon anti-corrosion coating, commercially known as Galvalume�. The corrosion resistance of our steel is so outstanding, even our unpainted panels carry a 30 year limited warranty. We use this same high performance steel with our 300 and 500 series paint systems, giving you the highest level of corrosion resistance you can get in the industry. Beware of metal roofing that is not MCA certified as it could be constructed with inferior steel and paint systems. Many companies will advertise a paint warranty, but the underlying metal will not be warranted against corrosion. Be sure to ask about base metal warranties before you buy.