Galvalume Roof: Lifespan, Bare vs. Painted and What to Avoid
Updated · By the Roof to Footing editors
A Galvalume roof is a steel roof whose panels are coated with an alloy of about 55% aluminum, 43.4% zinc and 1.6% silicon. That coating protects the steel better than the plain zinc on galvanized steel in most climates, which is why most painted metal roofing sold in the U.S. today is Galvalume underneath. Bare Galvalume panels have a silver, slightly spangled look; painted ones come in dozens of colors.
Galvalume vs. galvanized
| Galvalume (AZ50 or AZ55) | Galvanized (G90) | |
|---|---|---|
| Coating | Aluminum-zinc alloy | Zinc |
| How it protects | Aluminum forms a barrier; zinc protects cut edges | Zinc corrodes first to protect steel |
| Life in normal climates | Longer | Shorter |
| Cut edges | Some edge staining, slow to spread | Self-heals small scratches better |
| Concrete and animal contact | Avoid; alkaline conditions attack the aluminum | More tolerant |
| Typical use | Homes, commercial roofs, sheds | Livestock barns, agricultural buildings |
The "AZ" number is the coating weight. AZ55 has a heavier coating than AZ50, and many manufacturers require AZ55 for their bare-panel warranties.
Bare or painted?
- Bare (unpainted) Galvalume costs less and suits barns, shops and modern farmhouse styles. Its look changes over the first years as the surface dulls.
- Painted Galvalume adds a primer and finish coat. Silicone-modified polyester (SMP) is the budget paint; PVDF (sold as Kynar 500 or Hylar 5000) holds color longer and carries longer fade warranties.
On a house, painted is the usual choice. Light colors stay cooler and can qualify as cool roofs.
What damages a Galvalume roof
- Wet concrete, mortar, stucco or lime. The alkalinity attacks the aluminum in the coating. Don't store panels on concrete or let masonry dust settle on them.
- Copper and lead. Water running off copper flashing or a copper cap, or lead flashing touching the panels, corrodes the coating.
- Pressure-treated lumber touching the panels, especially when wet.
- Animal confinement. Ammonia from livestock buildings shortens coating life; galvanized or specially coated panels are used there.
- Marine salt spray. Very close to the ocean, aluminum or specially rated panels last longer.
Lifespan
A properly installed Galvalume roof in a normal climate commonly lasts 40 years or more, and manufacturers' warranties on the substrate often run 20 to 25 years for bare panels with paint warranties of up to 40 years on PVDF finishes. Fastener choice matters as much as the steel: on exposed-fastener panels, the rubber washers under the screws usually need attention long before the panels do.
Panel styles
Galvalume comes as exposed-fastener panels (corrugated, R-panel, PBR) and as concealed-fastener standing seam, including snap lock. Match gutters, flashing and trim to the roof. Galvalume gutters are a common pairing, and they share the same rules about copper and concrete.
Hail
Steel roofs hold up to hail far better than shingles, but hail can dent them. Thicker panels (24 gauge rather than 29) dent less. If hail is common where you live, read our guide to hail damage on metal roofs before you buy; insurance terms for cosmetic dents matter.