What Is Galvalume Coated Steel?
Galvalume is the trade name for sheet steel carrying a corrosion-resistant coating of nominally 55% aluminum and 43% zinc, applied in a continuous hot-dip process; Sheffield Metals states the composition as 55% aluminum, 43.4% zinc, and 1.6% silicone. The ASTM coating weights are the grades that matter on a quote: AZ50 and AZ55 are 0.50 and 0.55 oz/ft² total both sides (triple-spot). The warranty follows the grade. The mill-standard bare-Galvalume warranty runs 20 years 6 months for AZ50 and 25 years 6 months for AZ55, against rupture, structural failure, or perforation due to corrosion — Sheffield calls the 25.5-year substrate (perforation) warranty Galvalume's number-one selling point, and notes substrate warranties across manufacturers range from 15 to 25.5 years. Above the mill standard, individual manufacturers set their own terms: Taylor Metal warrants AZ-55 25 years against perforation, Mueller passes through a 40-year term on unpainted Galvalume Plus, Metal Sales warrants acrylic-coated AZ55 for 45 years, and Central States lists a 50-year Galvalume perforation term — so the number a buyer actually gets depends on whose panel it is. The exclusions are where warranties die: Galvalume is not suitable where animals are housed (manure breaks down into ammonia gas that reacts with the coating); salt and marine atmospheres are excluded, with the setback differing by manufacturer (Metal Sales draws it at 1,500 feet of salt water; Mueller at two linear miles); water runoff from lead or copper flashings, or metallic contact with lead or copper, is excluded; so is deterioration from contact with green, wet, or pressure-treated lumber; and so are roof sections flatter than 1/4:12 slope. U.S. Steel's own technical bulletin recommends against Galvalume in contact with lead, graphite, cement, or copper — including treated lumber containing copper — and in animal confinement or seawater-proximity environments.
Important Distinction
Note: Galvalume is a substrate coating, not a paint and not a panel: GALVALUME is a registered trademark of BIEC International Inc., and its warranty is issued by the steel producer or panel manufacturer through their registration process — Zilker Roofing installs panels made from it and quotes those terms; it does not issue them. The famous "25-year" figure is really 25 years 6 months, applies to the AZ55 coating weight (AZ50 is 20 years 6 months), covers perforation/structural failure from corrosion — not appearance — and is voided by conditions that are common in real projects: animal-confinement buildings, salt atmospheres (the setback distance differs by manufacturer), contact or runoff from copper or lead, treated lumber contact, and roof slopes flatter than 1/4:12.
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Also Known As
These are the search terms and phrases that commonly refer to this topic, so you can find it however you describe it.
How Galvalume Coated Steel Relates to Other Topics
Galvalume is the substrate under most modern steel metal roofs: the aluminum-zinc coating grade (AZ50 vs AZ55) sets the corrosion warranty before any panel or paint decision is made.
The metal-vs-shingle lifespan argument rests on the substrate: Galvalume's aluminum-zinc coating is what backs metal's multi-decade corrosion warranties.
Galvalume's warranty exclusions are also its repair rules: copper or lead contact, treated lumber, and runoff from dissimilar metals corrode the coating, so repairs must not introduce them.
Related To Galvalume Coated Steel
Paint and substrate are separate warranty layers on the same panel: a Kynar-class PVDF finish protects the surface of the Galvalume-coated steel beneath it, and each layer's coverage runs on its own clock.
The substrate layer of the metal-roof warranty stack is the Galvalume perforation warranty — 25 years 6 months for AZ55 at the mill standard, longer under individual manufacturers' terms.
Questions about Galvalume Coated Steel?
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