What Is Galvalume? Galvalume vs. Galvanized Steel for Metal Roofing

If you've been getting quotes for metal roofing panels, you've probably seen both “Galvalume” and “galvanized” mentioned without much explanation. Both terms refer to a protective coating applied to steel to prevent rust — but they're quite different in composition, performance, and where each belongs.

Here's a clear breakdown.

Galvanized steel has been around for over 150 years. The process is straightforward: steel sheet is passed through a bath of molten zinc. The zinc bonds to the steel surface and creates a barrier between the steel and the elements.

When zinc corrodes, it does so sacrificially — meaning it corrodes preferentially instead of the steel beneath it. This sacrificial protection is one of zinc's most useful properties, and it's especially valuable at cut edges and scratches, where the coating has been breached. The zinc around the damage migrates to protect the exposed steel, which slows the formation of rust.

The most common specification you'll see in metal roofing is G-100 galvanized (sometimes written as G100), which refers to a coating weight of 1.00 ounce per square foot total (both sides combined).

Galvalume was developed in the early 1970s as an improvement on galvanized for long-term atmospheric corrosion resistance. Instead of a pure zinc coating, Galvalume uses an aluminum-zinc alloy coating: approximately 55% aluminum and 45% zinc by area (with a small amount of silicon for adhesion).

The aluminum component does something zinc alone cannot: it forms a dense, tightly adhering oxide layer on the surface that acts as a barrier coating, physically blocking moisture and oxygen from reaching the steel beneath. Zinc provides sacrificial protection; aluminum provides barrier protection. Together, they outperform either material alone in most atmospheric exposure conditions.

The most common Galvalume specification you'll see is AZ50, which refers to a coating weight of 0.50 ounces per square foot (both sides combined). Despite being a lighter coating weight than G-100 galvanized, AZ50 Galvalume has been shown in independent testing to last significantly longer in atmospheric exposure — because the aluminum component changes the fundamental protective mechanism.

In most metal roofing applications — exposed to rain, snow, sun, and seasonal temperature swings — Galvalume outperforms galvanized for corrosion resistance and coating longevity. This is well-documented in industry testing and is the reason the metal roofing industry has largely shifted to Galvalume as the default substrate for painted and unpainted panels.

However, there is a meaningful exception.

Where galvanized holds an advantage:

Galvanized steel performs better in direct contact with certain chemical environments — specifically, environments with high ammonia or urea concentrations, which are common in active livestock operations. Animal waste, fertilizers, and the ammonia-rich atmosphere inside a heavily stocked barn can attack aluminum-based coatings. In those conditions, the sacrificial zinc in galvanized steel holds up better than the aluminum-zinc alloy in Galvalume.

This is why G-100 galvanized is sometimes specified for applications like:

All four of our profiles — Tuff Rib Ag (both finishes), Commercial PBR Panel, Snap Lock Standing Seam with Striations, and Standing Seam with Nail Flange — are manufactured on AZ50 Galvalume as the standard substrate. This is the right choice for the vast majority of roofing and wall applications in New England's climate.

For the Tuff Rib Ag profile, we also offer G-100 galvanized as an option, specifically for customers with agricultural applications where ammonia exposure is a concern.

Galvalume can be used in two ways: bare (unpainted) or color-coated.

Bare Galvalume — sometimes called AZM (aluminum-zinc-coated) — has a distinctive dull metallic finish. It reflects heat well and provides excellent corrosion resistance without a paint layer. It's used in some agricultural and industrial applications where appearance is secondary. Bare Galvalume is not recommended for areas with direct contact with dissimilar metals, concrete, or treated lumber, which can accelerate corrosion.

Color-coated Galvalume — which is what most of our customers order — has a paint system applied over the Galvalume substrate. For Tuff Rib Ag and PBR, that's WeatherXL paint. For standing seam profiles, it's Kynar. The paint layer provides additional UV protection, seals the surface, and allows for color selection.

When you hear “Galvalume steel with WeatherXL paint” or “Galvalume with Kynar,” the Galvalume is the substrate — the structural coating that protects the steel — and the paint layer sits on top of it for aesthetics and additional protection.

This matters practically: the Red Dot Galvalume warranty applies to panels made with the Galvalume substrate. It covers the base metal against perforation due to corrosion for a defined period.

If you order panels on a galvanized substrate rather than Galvalume, the Red Dot Galvalume warranty does not apply — you're under a different warranty covering the galvanized coating. Make sure you understand which substrate you're ordering if the warranty matters to your project.

For most metal roofing projects — residential, commercial, and general agricultural — Galvalume is the right default. It provides better long-term corrosion resistance in atmospheric exposure, and it's the substrate all four of our standard profiles are built on.

If you're building or re-roofing an active livestock facility and you have areas with direct or near-direct contact with animal waste, it's worth discussing galvanized panels (or at minimum, galvanized base trim) with your contractor.

When in doubt, tell us what the application is — we're happy to recommend the right substrate for your situation.

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