By The Roofing Brief Team. Last reviewed: October 2026.
A galvalume metal roof is steel sheet hot-dip coated with an alloy of roughly 55% aluminum, 43.4% zinc and 1.6% silicon, made to ASTM A792 in coating weights such as AZ50 (0.50 oz per sq ft, both sides) and AZ55 (0.55 oz per sq ft). Per the Cleveland-Cliffs GALVALUME product data sheet, an AZ50 coating gives at least twice the corrosion protection of G90 galvanized and a projected 40 to 60 year service life in rural and industrial air. The same mill literature rules it out in three places: against wet concrete or mortar, in pig barns, and in salt spray near the coast.
For gauge choices and where plain galvanized still makes sense, see our guide to steel roofs: galvanized vs galvalume and gauge.
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. Bethlehem Steel introduced the coating to construction in the early 1970s, per Sheffield Metals, and the technology is now licensed worldwide by BIEC International. In Australia the same 55% aluminum-zinc coating is sold by BlueScope as ZINCALUME steel. The steel gives the panel its strength; the coating does the corrosion protection.
The coating works two ways at once. As it cools, an aluminum-rich phase forms a network of dendrites and a zinc-rich phase fills the spaces between them, per the Cleveland-Cliffs data sheet. The aluminum gives barrier protection across the face of the panel, the zinc gives sacrificial (galvanic) protection at scratches and cut edges, and the silicon controls the Al-Fe-Zn-Si intermetallic layer that bonds the coating to the steel without a brittle, crack-prone layer.
Galvalume specs: coating weight, reflectance and heat limits
The numbers that separate galvalume from galvanized are published by the steel mills themselves. Every row below comes from a named mill or seller document, and the calculated thickness figures are the mill’s own conversion (1 oz per sq ft of galvalume equals 3.2 mils of coating, total both sides).
| Spec | Galvalume | Galvanized G90 | Source |
|---|---|---|---|
| Coating alloy | 55% aluminum, about 43% zinc, balance mainly silicon (about 1.6%) | Zinc | U.S. Steel GALVALUME bulletin; Cleveland-Cliffs |
| Coating weight, total both sides (minimum triple spot) | AZ50: 0.50 oz/sq ft; AZ55: 0.55 oz/sq ft | G90: 0.90 oz/sq ft | Cleveland-Cliffs coating thickness table |
| Calculated coating thickness per side | AZ50: 0.80 mil; AZ55: 0.88 mil | 0.77 mil | Cleveland-Cliffs coating thickness table |
| Typical use of each weight | AZ50 under paint; AZ55 for bare, acrylic-coated panels | Not applicable | Sheffield Metals; Iron Rod Steel listing |
| Corrosion protection | AZ50 gives at least 2 times the protection of G90 | Baseline | Cleveland-Cliffs |
| Projected service life | At least 35 years before major maintenance; 40 to 60 years in industrial and rural environments | About half of galvalume at equal coating thickness | Cleveland-Cliffs |
| Bare solar reflectance (initial / 3 years) | 0.78 / 0.58; SRI 75 / 34; thermal emittance 0.08 | Not listed | Cleveland-Cliffs Table 1 |
| Heat discoloration | No discoloration up to 600°F | Begins to discolor around 450°F | Cleveland-Cliffs |
| Fire | Flame spread 0, smoke developed 0 | Not listed | Cleveland-Cliffs |
| Substrate warranty on a retail bare panel | 25 years (26-gauge AZ55 R-panel) | Not listed | Iron Rod Steel, October 2026 |
Galvalume vs galvanized: the head-to-head
Galvanized steel is coated in zinc only; galvalume replaces most of that zinc with aluminum. Cleveland-Cliffs rates an AZ50 galvalume coating at no less than twice the corrosion protection of G90 galvanized, and Sheffield Metals puts the gap at two to four times. The trade-off sits at cut edges in the early years: galvanized may show less red rust at edges for up to about 10 years, depending on the environment, before its zinc wears away faster than galvalume, per Cleveland-Cliffs. Price between the two is close, so the choice is driven by environment.
| Factor | Galvanized (G90) | Galvalume (AZ50/AZ55) |
|---|---|---|
| Coating | ~100% zinc | 55% aluminum, 43.4% zinc, 1.6% silicon |
| General corrosion resistance | Baseline | At least 2 times better (Cleveland-Cliffs); 2 to 4 times (Sheffield Metals) |
| Unpainted lifespan | About half of galvalume at equal coating thickness | 40 to 60 years projected in rural and industrial air |
| Cut-edge protection | Less edge rust in roughly the first 10 years | Slight edge rust that stops spreading |
| Concrete / masonry contact | Tolerates better | Corrodes rapidly, worst while concrete cures |
| Animal confinement (ammonia) | Preferred for pig barns | Ruled out for pig barns; cattle, poultry and horse buildings only with ventilation and waste management |
| Cost | Similar per sq ft, same gauge | Similar per sq ft, same gauge (Cleveland-Cliffs, prepainted) |
The cut-edge behavior is the nuance most vendor pages skip. On galvalume, a small amount of red rust at sheared edges is normal. The U.S. Steel GALVALUME bulletin charts edge creep on prepainted panels at acid rain, non-marine, subtropical and industrial test sites and reports that it is slight and stops increasing after 2 years. On galvanized, the zinc runs to protect the edge more aggressively but the whole coating depletes faster. Our deeper look at galvanized vs galvalume roofing walks through each factor in the table above.
How long does galvalume last?
Cleveland-Cliffs projects that galvalume gives at least 35 years before major maintenance and a 40 to 60 year service life in industrial and rural environments, based on flat-coupon exposure tests run for 36 years in the USA and 17 years in Canada plus inspections of buildings up to 25 years old. U.S. Steel adds that for most environments the full lifetime of bare galvalume has not yet been determined. Galvanized at the same coating thickness reaches first red rust in roughly half the time in the Bethlehem Steel coupon data that Cleveland-Cliffs charts.
Coating weight matters. AZ55 carries 0.55 oz of aluminum-zinc per sq ft, about 0.88 mil per side, against 0.50 oz and 0.80 mil for AZ50. Sheffield Metals and Iron Rod Steel both describe AZ55 as the spec for bare, acrylic-coated panels and AZ50 as the spec under paint, where the paint film adds protection. For how these numbers compare with asphalt, tile, and slate, see our roofing material lifespan report.
Where galvalume fails: the three environments to avoid
Galvalume’s aluminum content is its strength in open air and its weakness in a few specific settings. The U.S. Steel bulletin lists contact with lead, graphite, cement or copper (including treated lumber containing copper), proximity to seawater, very long wet times, chronic chemical exposure and animal confinement as conditions where it recommends not using galvalume or taking precautions. Cleveland-Cliffs adds bulk potash fertilizer storage and pig barns as outright exclusions.
| Environment | What attacks the coating | What to do | Source |
|---|---|---|---|
| Concrete, mortar, masonry contact | High alkalinity dissolves the aluminum oxide layer, fastest while concrete cures | Isolate the panels, or use galvanized at sustained-contact points | Cleveland-Cliffs; BlueScope bulletin CTB-16 |
| Pig barns and bulk potash fertilizer storage | Corrosive gases from waste, high humidity | Do not use galvalume, bare or prepainted | Cleveland-Cliffs |
| Cattle, poultry and horse buildings | Ammonia and other gases from decomposing manure | Galvalume only with proper waste management, ventilation and insulation; confirm the maker’s warranty terms | Cleveland-Cliffs; U.S. Steel |
| Copper, lead, copper-bearing treated lumber | Accelerated corrosion at the contact area and under copper runoff | Separate the metals; no lead-headed nails, lead washers or lead flashing | Cleveland-Cliffs; U.S. Steel |
| Coastal / heavy salt spray | Chlorides accelerate coating breakdown | Aluminum, or check the warranty distance limit before ordering | Sheffield Metals |
Masonry and concrete contact
The aluminum-zinc coating corrodes rapidly in highly alkaline conditions. Cleveland-Cliffs states that bare and prepainted galvalume suffer rapid corrosion in contact with mortar and concrete, especially during the curing phase, and BlueScope’s bulletin CTB-16 says ZINCALUME steel is not recommended for immersion in wet cement. 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 and other corrosive gases. Cleveland-Cliffs rules out bare and prepainted galvalume for pig barns, which it calls severely corrosive, but says cattle, poultry and horse buildings can use galvalume with proper waste management, ventilation, insulation and design. The U.S. Steel bulletin is stricter and lists animal confinement among the uses where it recommends not using galvalume or taking precautions. Ask the panel maker for its livestock exclusion in writing before you order. 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. Sheffield Metals states that substrate and paint warranties are not available on galvalume within 1,500 feet of a coast, and the U.S. Steel bulletin lists proximity to seawater among the conditions that need precautions. Inside that distance, solid aluminum roofing is the usual alternative. 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: Cleveland-Cliffs says prepainted galvalume is typically available at a similar price per square meter, same gauge, as prepainted galvanized. The bigger price step is paint. In October 2026, Iron Rod Steel in Houston listed 26-gauge bare AZ55 galvalume R-panel at $2.95 per linear foot and 26-gauge AZ50 R-panel painted with Sherwin-Williams WeatherXL SMP at $4.15 per linear foot, both with a 36 in. cover width.
| Worked example: panels only | Bare galvalume (AZ55) | Painted galvalume (AZ50, SMP) | Source or input |
|---|---|---|---|
| Price per linear foot, 26 gauge, 36 in. cover | $2.95 | $4.15 | Iron Rod Steel listings, October 2026 |
| Price per sq ft of coverage | $0.98 | $1.38 | Price divided by 3 sq ft per linear foot |
| 2,000 sq ft roof plus 10% waste (2,200 sq ft) | 733 linear ft | 733 linear ft | 2,200 / 3; waste factor is an assumption |
| Panel cost | $2,163 | $3,043 | 733.3 x price |
| Difference | $880 more for the painted panels | Calculated | |
That example excludes trim, screws, foam closures, underlayment and labor, which make up most of an installed price. Standing seam and exposed-fastener corrugated sit at opposite ends of the installed range, and our guide to standing seam vs exposed fastener metal roofs breaks down the gap. Because galvalume sits inside the general steel-roofing band, use a full breakdown such as our metal roof cost guide for installed pricing by region. Gauge moves the number as much as the coating does: Iron Rod Steel lists 26 gauge at 0.0185 in. thick against about 0.0142 in. for 29 gauge.
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; Sheffield Metals notes the light acrylic film wears off with exposure and scuffs under foot traffic. 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. U.S. Steel says bare galvalume is typically painted only for appearance on steep-slope roofs. Painted panels are standard for residential standing seam; bare galvalume is common on agricultural and utility exposed-fastener roofs, which are typically screw-down metal roofs.
- Bare galvalume: lowest cost ($2.95 per linear foot for 26-gauge R-panel at Iron Rod Steel, October 2026), AZ55 coating, 25-year substrate warranty on that listing, and a silver finish whose solar reflectance falls from 0.78 to 0.58 over 3 years per Cleveland-Cliffs. Best for outbuildings and utility roofs.
- Painted galvalume: color options over an AZ50 coating; $4.15 per linear foot with a 40-year limited SMP paint warranty on the same retailer’s 26-gauge R-panel. PVDF (Kynar 500) systems are the premium tier for fade and chalk resistance and are standard for homes.
Should you choose galvalume?
Choose galvalume for most residential and commercial metal roofing outside the environments in the table above: Cleveland-Cliffs projects 40 to 60 years of service at a price similar to galvanized. Choose galvanized instead for a pig barn or where the roof stays in contact with masonry. Within 1,500 feet of the coast, where Sheffield Metals says galvalume warranties are not available, step up to solid aluminum. The decision table below follows that logic.
| If your building… | Specify | Why |
|---|---|---|
| Houses pigs or stores bulk potash fertilizer | Galvanized or another maker-approved substrate, not galvalume | Cleveland-Cliffs lists both as exclusions |
| Houses cattle, poultry or horses | Galvalume only with ventilation, waste management and the maker’s written approval | Cleveland-Cliffs allows it with those conditions; U.S. Steel advises precautions |
| Has panels touching or draining onto concrete, mortar or masonry | Isolate the panels, or galvanized at sustained-contact points | Rapid corrosion during curing (Cleveland-Cliffs) |
| Has copper gutters, copper or lead flashing, or copper-treated lumber at contact points | Separate the metals; 300 Series stainless or capped fasteners | Accelerated corrosion at contact and under copper runoff (Cleveland-Cliffs) |
| Mixes galvalume with bare galvanized parts | Put galvalume downstream of the galvanized, never above it | Runoff from galvalume causes drip corrosion of galvanized (Cleveland-Cliffs) |
| Is within 1,500 ft of the coast | Aluminum | Galvalume substrate and paint warranties not available (Sheffield Metals) |
| Is a home anywhere else | Painted galvalume, AZ50 | Color and paint warranty over a 40 to 60 year substrate |
| Is a shed, carport or barn without livestock anywhere else | Bare galvalume, AZ55 | Lowest panel price; 25-year substrate warranty on the retail example |
- Roof over pigs, or against concrete or masonry? Specify galvanized.
- Within 1,500 feet of the coast? Specify aluminum.
- Everything else? Specify galvalume, painted for homes and bare for utility roofs.
If you are still weighing galvalume against other materials by budget and lifespan, our roof material calculator compares them before you request quotes.
Galvalume roofing: frequently asked questions
What is the difference between galvalume and galvanized?
Galvanized steel is coated with zinc alone, while galvalume is coated with an alloy of about 55% aluminum, 43.4% zinc, and 1.6% silicon. Cleveland-Cliffs rates an AZ50 galvalume coating at no less than twice the corrosion protection of G90 galvanized, while galvanized can show less red rust at cut edges for roughly the first 10 years and is the substrate to use in pig barns, where galvalume is ruled out.
How long does a galvalume roof last?
Cleveland-Cliffs projects at least 35 years before major maintenance and a 40 to 60 year service life in industrial and rural environments, based on flat-coupon exposure tests run for up to 36 years. U.S. Steel says the full lifetime of bare galvalume has not been determined for most environments. Painted panels carry separate finish warranties, such as the 40-year limited SMP paint warranty on one 26-gauge retail R-panel.
What is galvalume coating made of?
Galvalume coating is an aluminum-zinc alloy of roughly 55% aluminum, 43.4% zinc, and 1.6% silicon by weight, applied to steel sheet through a continuous hot-dip process to ASTM A792. Common coating weights are AZ50 (0.50 oz per sq ft, both sides) for painted sheet and AZ55 (0.55 oz per sq ft) for bare sheet. The aluminum forms a barrier oxide layer, the zinc provides sacrificial protection at scratches and cut edges, and the silicon controls how the alloy bonds to the steel.
Where should you not use galvalume?
Avoid galvalume in contact with wet concrete, mortar, lead, copper or copper-bearing treated lumber; in pig barns and bulk potash fertilizer storage, which Cleveland-Cliffs rules out; and within 1,500 feet of a coast, where Sheffield Metals says substrate and paint warranties are not available. Cattle, poultry and horse buildings can use it only with proper ventilation and waste management, per Cleveland-Cliffs.
Does galvalume rust?
Yes, but slowly. A small amount of red rust at sheared or cut edges is normal, and U.S. Steel reports that edge creep on prepainted galvalume is slight and stops increasing after 2 years. Across the panel face, Cleveland-Cliffs projects at least 35 years before major maintenance in rural and industrial air; contact with copper, lead or wet concrete, or salt spray near the coast, shortens that.
Is galvalume more expensive than galvanized?
Not by much. Cleveland-Cliffs says prepainted galvalume is typically available at a similar price per square meter, same gauge, as prepainted galvanized. The bigger price gap is paint: in October 2026 Iron Rod Steel listed 26-gauge bare galvalume R-panel at $2.95 per linear foot and the painted version at $4.15. Profile and gauge affect installed price more than the coating does.