What is metal roofing made of?
Short answer. Most residential metal roofing is steel coated with Galvalume, an aluminum and zinc alloy, or with zinc galvanizing, then primed and painted. Other options are aluminum, copper and zinc, and stone-coated steel adds an acrylic layer and stone granules over the coated steel.
Inside a painted steel panel
- Steel core. Sheet steel, measured in gauge. Residential panels usually run 29 to 24 gauge.
- Metallic coating. Galvalume or galvanized zinc bonded to both sides. This is what stops rust, and the coating weight is listed on spec sheets.
- Pretreatment and primer. Help the paint bond and slow corrosion at scratches.
- Topcoat. The color layer. PVDF finishes resist fading and chalking best, SMP (silicone-modified polyester) costs less and fades sooner, and plain polyester is the budget option.
- Backer coat. A thinner coat on the underside.
Other metals
- Aluminum. Naturally corrosion resistant, light, and preferred near salt water. Softer and more prone to hail dents.
- Copper. Weathers to brown, then green. Very long lived and expensive.
- Zinc. Forms a protective patina and self-heals light scratches. Common in Europe, rare on Georgia homes.
- Stone-coated steel. Coated steel with an acrylic base and bonded stone granules. Quieter and better at hiding small dents.
Compatibility cautions
Water running off copper onto Galvalume or aluminum corrodes them, so keep copper flashings and gutters away from those panels. Galvalume also should not sit in contact with wet mortar or concrete. Fasteners should be coated to match the panel, and exposed screws use rubber washers that age over time.
What it means in Georgia
Inland North Georgia is easy on coated steel, so Galvalume with a good finish is the common pick. Humidity and red clay dust are more of a finish and cleaning issue than a corrosion one.
For the full comparison with shingles, see metal roofing in Georgia.