The Role of Galvanization and Coatings in Long-Lasting Metal Roofs

Metal roofs are known for strength and long life. But the real reason they last isn’t just the steel. It’s the layers that protect that steel: the metallic coating (like galvanization) and the paint system on top. 

In this quick guide, we’ll explain how those layers work together, why Butler-Cote™ is a premium option, how it compares to other coatings, what standards to look for, and which choices fit different U.S. climates and building types.

Why metal rusts—and how we stop it

Steel is strong but will rust when water and oxygen reach it. To prevent this, manufacturers add two shields:

1. A metallic coating bonded to the steel (galvanized zinc or aluminum-zinc “Galvalume®”).
2. A factory paint system that seals out sun, water, chemicals, and dirt.

When both shields are chosen well, a metal roof can protect a building for decades with low maintenance.

Metallic coatings 101: Galvanized vs. Galvalume®

Galvanized (zinc-coated) steel protects the base metal by sacrificing itself first. It’s tough and proven. Higher zinc weights (like G90 in the ASTM A653 standard) mean thicker protection.

Galvalume® (aluminum-zinc alloy) mixes aluminum and zinc. The aluminum forms a hard barrier; the zinc still offers “sacrificial” protection at scratches and cut edges. In most environments—especially warm, humid, or slightly industrial—Galvalume typically lasts longer than plain galvanized. That’s why many commercial standing-seam roofs use AZ50/AZ55 material made to ASTM A792.

Bottom line: If you’re inland with mild conditions, G90 galvanized can perform well. If you’re in high humidity, mixed pollution, or near salt air, Galvalume usually wins on long-term corrosion resistance.

Why coatings (paint systems) matter so much

Even the best metallic layer needs a quality topcoat to block UV, moisture, and grime.

• PVDF (Kynar 500® / Hylar 5000®) fluoropolymer is the gold standard for color stability and chalk resistance. It keeps color and gloss for a very long time—even in harsh sun.
• SMP (silicone-modified polyester) is a solid mid-tier option. It’s more affordable, but it fades and chalks sooner in strong UV.

Where Butler-Cote™ fits

Butler-Cote™ is Butler’s full-strength PVDF finish (70% resin). It’s designed to resist chalking, fading, cracking, and peeling and comes with a 25-year, non-prorated finish warranty on standard colors. That warranty also sets strict limits on color change and chalk over time—one reason architects and owners choose it for visible, long-life projects.

PVDF vs. SMP in plain terms:

• Want the color to look great in year 20? Choose PVDF (Butler-Cote).
• Need a budget option where looks matter less? SMP can work, especially in low-UV regions.
• In very sunny places (Southwest, Gulf states), PVDF keeps its appearance far better than SMP.

The standards that signal quality

Knowing a few common standards helps you compare apples to apples:

• ASTM A653 / A792 – Base metal with galvanized (A653) or aluminum-zinc (A792) coatings (e.g., G90, AZ55).
• ASTM A755 – Requirements for pre-painted metallic-coated steel for buildings.
• ASTM D2244 / D4214 – How manufacturers measure fade (ΔE) and chalk over time.
• UL 790 – Fire classification for roof coverings (Class A is highest).
• UL 2218 – Hail impact resistance (Class 4 is highest).
• FM 4470/4471 – Roof assembly approvals for wind, fire, hail (often required by insurers).
• CRRC / ASTM E1980 – “Cool roof” ratings using Solar Reflectance Index (SRI). Many Butler colors are ENERGY STAR® “cool roof” options and can reach very high SRI values to cut cooling loads.

What to choose by climate (U.S. regions)

Coastal & marine (salt + humidity):

• Best: Galvalume (AZ50/AZ55) + PVDF.
• Use stainless or sealed fasteners and rinse salt deposits as part of maintenance.
• Very close to breaking surf? Consider aluminum for zero rust risk.

Hot, high-UV (deserts/Sunbelt):

• Corrosion risk is low; UV is the killer.
• Best: PVDF cool-color finish on galvanized or Galvalume.
• SMP can work to save cost, but expect earlier fade/chalk.

Cold & snowy (upper Midwest/Northeast/mountains):

• Metal roofs shine here. Corrosion is slower; design for snow loads, ice, and safe snow-shed.
• Best: Galvalume (painted or unpainted). PVDF adds flexibility and long-term color.
• Add snow guards where needed.

Humid subtropical (Southeast):

• Heat + humidity + storms demand strong barriers.
• Best: Galvalume + PVDF.
• Light “cool roof” colors help tame AC costs and keep performance stable.

What to choose by building type

Warehouses & distribution:

• Big roofs, cost control, reliability.
• Inland: Unpainted Galvalume (acrylic-coated) is a common, durable pick.
• Harsher climates or long design life: Upgrade to PVDF-painted Galvalume.

Retail centers & offices:

• Appearance and brand colors matter; roofs see foot traffic.
• Best: PVDF on Galvalume, often in cool colors.
• Confirm fire (UL 790), impact (UL 2218), and wind ratings (UL/FM).

Schools & institutions:

• Long life, low maintenance, energy goals, strong warranties.
• Best: PVDF on Galvalume with high SRI options.
• Many districts standardize on standing-seam Galvalume with PVDF for 30–50+ year service.

Quick checklist when you spec a metal roof

1. Pick the right base metal:
   • Mild inland = G90 or AZ50;
   • Humid/coastal = AZ50/AZ55 preferred.
2. Choose the paint system for your sun:
   • High UV or visible roofs = PVDF (Butler-Cote™);
   • Budget/low-UV = SMP acceptable.
3. Check the labels:
   • Look for ASTM designations on coil, UL/FM approvals for assemblies, and CRRC/ENERGY STAR for cool roof performance.
4. Match to climate:
   • Salt, humidity, UV, snow—let your environment guide your choices.
5. Think lifetime cost, not just first cost:
   • Premium coatings reduce repainting, keep buildings cooler, and protect value.

Where Butler-Cote™ stands out

• Finish quality: Full-strength PVDF chemistry for elite fade/chalk resistance.
• Warranty: 25-year, non-prorated finish warranty on standard colors, with strict limits for color change and chalk.
• Cool roof palette: ENERGY STAR®-rated colors can hit very high SRI, cutting cooling loads.
• System approach: Butler panels, clips, sealants, and finishes are designed to work together for long-term weathertightness.

The takeaway

• The metallic layer (galvanized or Galvalume) stops rust from reaching the steel.
• The paint system (PVDF or SMP) blocks UV, water, and chemicals and protects the look.
• For the longest life and best appearance, especially in tough climates, Galvalume + PVDF (Butler-Cote™) is hard to beat.
• Choose materials that match your climate, building type, and performance goals, and confirm the right ASTM/UL/FM boxes are checked.

Need parts, panels, or guidance?

We sell genuine Butler Manufacturing parts and can help you match panels, trims, finishes, and fasteners to your building and climate—whether you’re maintaining an older roof or planning an upgrade. Tell us your project location and goals, and we’ll spec the right roof that performs for decades.

Reach out!