Part 2 – A Closer Look at Metal Roofing

The Metal Roof Manufacturing Process

In this installment of A Closer Look at Metal Roofing, we’ll take a look at the very core of the metal roofing industry: the manufacturing process.

The use of metal in roofing dates as far back as the 3rd century B.C., with the copper shingles installed on top of the 162-foot-tall Loha Maha Paya temple in Sri Lanka. In the U.S., metal roofs are believed to have made their first appearance in the late 19th century. Time has brought a lot of changes to the way metal roofs are manufactured—from manual hammering to power hammering to power rolling.

It was Swedish mining engineer Christopher Polhem who revolutionized the large-scale production of metal roofs with his use of rolling machinery beginning around 1704. It allowed Polhem’s metal works to produce sheet metal roofing materials, the most important of which was tinned sheet. Then, in the 1750s, English ironmaster Henry Cort developed the roll-forming process, which became the basis of modern-day metal roof production.

Today, the metal roof manufacturing process begins with a coil of metal. Coatings of zinc or zinc-aluminum coating and primer are applied as needed. From this point onward, the process will depend on the specific format or profile the manufacturer wants to produce. Vertical panels are given a baked-on paint finish, rolled to form their characteristic ribs, and cut to specified lengths. Shingles and tiles, on the other hand, are given an acrylic-bonded stone chip or paint finish, cut into sections, and stamped.

The manufacturing process also has to factor in guidelines and specifications set by industry authorities, such as:

  • American Iron and Steel Institute. AISI is a U.S. trade association and a core member of the Metal Roofing Alliance. Their investigations into the performance of metals in roofing (among other industries) have allowed them to publish specifications for the production and installation of metal roofs and structural members.
  • ENERGY STAR. Because metal roofs are often promoted and sold as a green roofing option, they are subject to ENERGY STAR product specifications. Some of the performance metrics ENERGY STAR uses to evaluate metal roofs include:
    • Solar flux. A measure of the direct and diffused radiation a roof receives from the sun at ground level.
    • Solar reflectance. A measure of the amount of solar flux reflected by a roof’s surface.
    • Thermal emittance. A measure of how well a roof’s surface radiates heat away from itself compared with a blackbody radiator operating at the same temperature.

It pays to note that while metal in general performs better than many other roofing materials, the actual manufacturing process and product performance vary greatly from manufacturer to manufacturer. Not all metal roofs are created equal.