Galvalume metal roofing is steel coated with an aluminum-zinc alloy of roughly 55% aluminum, 43.4% zinc, and 1.6% silicon. That coating outlasts plain galvanized (zinc-only) steel by two to four times in most climates, but it fails fast in three specific places: against concrete or masonry, under animal-waste ammonia, and in heavy salt spray. This guide covers the coating chemistry, the head-to-head against galvanized, real lifespan numbers, cost, and exactly where galvalume is the wrong call.
For the broader steel-substrate picture (gauge choices, panel pricing, and galvanized use cases), see our guide to steel roofs: galvanized vs galvalume and gauge. This page goes deep on galvalume itself.
What is galvalume?
Galvalume is carbon steel sheet coated on both sides with an alloy of about 55% aluminum, 43.4% zinc, and 1.6% silicon by weight, applied through a continuous hot-dip line. The name is a trademark first commercialized by Bethlehem Steel in the 1970s. In Australia and parts of Asia the same coating sells as Zincalume. The steel gives the panel its strength; the aluminum-zinc coating does the corrosion protection.
The coating works two ways at once. Aluminum forms a stable oxide barrier that seals most of the surface, which is why galvalume resists general rusting far better than zinc alone. Zinc provides sacrificial (galvanic) protection at scratches and cut edges, corroding first to protect exposed steel. The silicon controls how the alloy bonds to the steel during dipping, preventing a brittle layer that would crack.
Galvalume vs galvanized: the head-to-head
Galvanized steel is coated in zinc only; galvalume replaces most of that zinc with aluminum. The result is a coating that lasts two to four times longer in general atmospheric exposure but sacrifices some of galvanized steel’s aggressive cut-edge and scratch protection. Cost between the two is close, so the choice is driven by environment, not price.
| Factor | Galvanized (G90) | Galvalume (AZ50/AZ55) |
|---|---|---|
| Coating | ~100% zinc | 55% aluminum, 43.4% zinc, 1.6% silicon |
| General corrosion resistance | Baseline | 2 to 4 times better |
| Unpainted lifespan | 15 to 25 years | 40 years or more |
| Cut-edge protection | Stronger sacrificial action | Weaker, but self-limiting |
| Concrete / masonry contact | Tolerates better | Corrodes rapidly |
| Animal-confinement (ammonia) | Preferred | Fails early |
| Cost | Roughly equal | Roughly equal, slight premium |
The cut-edge behavior is the nuance most vendor pages skip. On galvalume, a small amount of red rust at sheared edges is normal and expected. Because the aluminum-rich coating limits how far corrosion can travel, that edge rust tends to self-limit and stop rather than creep under the panel. On galvanized, the zinc runs to protect the edge more aggressively but the whole coating depletes faster.
How long does galvalume last?
Unpainted (bare Galvalume) roofing typically lasts 40 years or more, and painted galvalume panels commonly carry 30 to 40 year finish warranties on top of a longer substrate life. Real-world field lifespan runs 40 to 70 years depending on climate, coating weight (AZ50 vs AZ55), slope, and whether the roof ever contacts the materials that attack the coating. Galvanized, by contrast, gives 15 to 25 years unpainted in most climates.
Coating weight matters. AZ55 carries more aluminum-zinc per square foot than AZ50 and is the common spec for exposed roofing; thinner coatings are used where a paint system does most of the protecting. For a material-by-material view of how these numbers compare to asphalt, tile, and slate, see our roofing material lifespan report, which sets field data against manufacturer marketing claims.
Where galvalume fails: the three environments to avoid
Galvalume’s aluminum content is its strength in open air and its weakness in three specific settings. In each case the aluminum component is chemically attacked, and galvanized steel is the correct substrate instead. Naming these upfront is the point of this guide, because most sources bury them.
| Environment | What attacks the coating | Correct substrate |
|---|---|---|
| Concrete, mortar, masonry contact | High alkalinity dissolves the aluminum oxide layer | Galvanized |
| Animal confinement (barns, poultry, hog, dairy) | Ammonia from decomposing manure attacks aluminum | Galvanized |
| Coastal / heavy salt spray | Chlorides accelerate coating breakdown | Aluminum or coated galvanized |
Masonry and concrete contact
The aluminum-zinc coating corrodes rapidly in highly alkaline conditions, and wet concrete, mortar, and fresh masonry are strongly alkaline. Panels that sit against a block wall, get splashed with concrete slurry during construction, or drain onto a masonry parapet can show accelerated attack at those contact points. Isolate galvalume from masonry, or specify galvanized where sustained contact is unavoidable.
Animal confinement buildings
Decomposing manure releases ammonia gas, and ammonia chemically attacks the aluminum in the galvalume coating, causing premature failure. For chicken houses, hog barns, and dairy operations where livestock live under the roof, galvanized is the standard substrate. This is a documented exclusion in most galvalume warranties. Our barn roofing guide covers the panel and substrate choices for agricultural buildings in more detail.
Coastal and salt exposure
Chlorides in coastal salt air accelerate breakdown of the aluminum-zinc coating over time. Galvalume performs acceptably in many mild coastal settings but is not the first pick within roughly a mile of breaking surf or in salt-spray zones. In those conditions, solid aluminum roofing or a heavily coated system is the more durable choice. See our aluminum roofing guide for how aluminum compares on saltwater durability and cost.
Galvalume roof cost
Galvalume and galvanized are priced close enough that cost rarely decides between them; the coating you need is set by environment. Bare or painted galvalume panels commonly run in the same range as other steel roofing on a per-square basis, with standing-seam profiles costing well more than exposed-fastener corrugated. Expect installed metal roofing to land anywhere from a budget corrugated number to a premium standing-seam number depending on profile, gauge, and region.
Because galvalume’s price sits inside the general steel-roofing band, use a full metal-roof cost breakdown rather than a galvalume-specific number. Our metal roof cost guide lays out standing seam, corrugated, and per-square pricing by region, and the gauge you choose (24, 26, or 29) moves the number as much as the coating does.
Painted vs bare galvalume
Bare (Acrylume or acrylic-coated mill finish) galvalume shows its natural spangled metallic gray and relies entirely on the aluminum-zinc coating for protection. Painted galvalume adds a PVDF (Kynar 500) or SMP finish that provides color, extra UV resistance, and its own warranty, while the galvalume underneath still guards the cut edges. Painted panels are standard for residential standing seam; bare galvalume is common on agricultural and utility exposed-fastener roofs.
- Bare galvalume: lowest cost, 40-plus year substrate life, limited color, best for outbuildings and utility roofs.
- Painted galvalume: color options, PVDF finish warranties of 30 to 40 years, better fade and chalk resistance, standard for homes.
Should you choose galvalume?
Choose galvalume for most residential and commercial metal roofing away from the three failure environments; it delivers the longest life per dollar of any steel coating. Choose galvanized instead when the roof contacts masonry, sits over animal confinement, or needs the toughest cut-edge and dent behavior. In heavy coastal salt, step up to solid aluminum. The decision below follows that logic.
- Roof over livestock, or against concrete or masonry? Specify galvanized.
- Within a mile of breaking surf or heavy salt spray? Specify aluminum.
- Everything else, want the longest life per dollar? Specify galvalume, painted for homes and bare for utility roofs.
Reviewed by The Roofing Brief Team. Last reviewed July 2026.