Metal roofing examples (C) Daniel Friedman Galvanized Metal Roofing Types, Product Sources, Installation, Defects, Repairs

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This article describes galvanized metal roofing products and metals: metal roof choices, installation, inspection, metal roof defects, roofing repairs, and metal roof product sources.

Also see GALVANIC SCALE & METAL CORROSION and see METALS USED IN ROOFING and our metal roofing home page, METAL ROOFING.

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Galvanized Metal Roofing Materials, Choices, Costs, Life Expectancy, Characteristics

Galvanized metal roof, San Miguel de Allende, Mexico (C) Daniel FriedmanGalvanized iron or steel roofing - according to the US NPS, "Iron or steel are galvanized by coating them with zinc.

Rather than producing the simple coating created by tinplating, a rust resistant alloy of the two metals forms on the surface.

In 1839, two years after galvanizing was patented in Europe, the material was used on the roof of the Merchants Exchange in Manhattan.

To protect against corrosion, the steel is bonded to a layer of zinc, which works as a sacrificial coating on the surface and also offers some protection to cut edges and nicks by flowing to these areas. The heavier the zinc coating, the longer the protection.

The Metal Roofing Alliance recommends G-90 galvanized steel for roofing, which has 90 ounces of zinc per square foot.

Our metal roof photo (above left) shows galvanized steel metal roofing used on both roof and the side of a small building in San Miguel de Allende.

Unpainted G-90 galvanized steel is typically warranted against corrosion for 20 years under normal conditions.

It often lasts longer, but it may show visible corrosion in as few five years under harsh conditions, such as salt spray, significant air pollution, or low-slope applications in wet climates. Field cuts made with an abrasive saw are prone to corrosion.

Though the sheet iron was hand dipped in the zinc, much as it was in tin, larger sheets were used (24 by 72 inches in the 1850s). This meant fewer joints, and when used as corrugated sheets, less supporting framing.

Even as the production of galvanized iron and steel roofing products increased, the price remained higher than that of other metals. The price differential did not shrink sufficiently for galvanized roofing to exceed tin and terneplate in popularity until the 20th century. "

Iron and steel roofing - according to the US NPS, "Both iron and steel without any plating were used for roofing. The Philadelphia home of the mill owner who rolled the first sheet iron in the United States was roofed in the material around 1794.

Iron replaced slate on the White House in 1804. Because it was available in large sheets, rather than the small sheets used for plated material, it required fewer joints. Some manufacturers produced factory painted material, but late19th century accounts indicate that paint was an inadequate defense against the corrosive effects of the atmosphere in industrial regions."

Galvalume®: Metal Roof Products Similar to Galvanized Roofing

Also see Aluminized Steel Roofs. Aluminized steel generally outlasts galvanized steel but has largely been replaced in the market by Galvalume®.

Also sold under the trade names Zincalume ® and Galval®, Galvalume® was developed in the early 1970s. The underlying steel is coated with a zinc aluminum alloy that combines the long-lasting protection of aluminum with the self-healing properties of zinc.

It also has the reflective qualities of aluminum, reducing attic temperatures and cooling loads. The most common application weight is AZ 55, which has about a 1-mil-thick coating on each side. Unpainted Galvalume® is warranted against corrosion for 20 years, but it has stood up well in weathering tests for 30 years and is projected to last up to 40 years under normal conditions.

Cut edges hold up very well, but cutting the material with an abrasive blade is discouraged as the filings will mar the surface. Galvalume® costs about 10% more than standard galvanized steel.

Steel metal roofing, including Galvalume Metal Roofing. Quoting from the Metal Roof Alliance:

Galvalume steel is an ideal roofing material because of its strength, extraordinary outdoor corrosion resistance and longevity. Steel roofing used in residential applications today is metallic coated with either Zinc (G90) or Zinc/Aluminum (AZ50) to provide the corrosion resistance homeowners desire. Steel roofing is strong and therefore gives higher wind uplift resistance and a broader range of application than other roofing materials.

As a result, an installed steel roof system has a broader range of price levels and products than many other kinds of metal roofing. Steel roofs have passed the UL 90 wind tests due to their strength and weight. For additional test results, visit to view the reports done at FL Solar Energy Center in their Flexible Roofing Facility.

Steel Roof ShingleToday's quality steel roofing offers excellent rust protection as well. Galvanized steel roofing is available painted, aggregate-coated, or with a mill or bare finish. Unlike conventional non-metallic roof systems, Galvalume steel roofs won't crack and peel when subjected to the sun and weather.

-- Adapted and expanded with permission from Best Practices Guide to Residential Construction. Also see METALS USED IN ROOFING.

Metal Roofing Sources, Products, & Manufacturers

Best Practices Guide to Residential Construction lists these producers and sources of metal roofing, metal roof fastening systems, and related metal roofing products

  • Classic Products, website:
    Modular metal shingle panels and standing seam panels
  • Decra Roofing Systems, website:
    Modular metal shingle, tile, and shake panels
  • Dura-Lok Roofing Systems, website:
    Modular metal roofing shingles with granular coating
  • Fabral, website:
    Exposed fastener and concealed clip metal roofing panels
  • Follansbee Roofing, Follansbee WV 26037, Tel: 800-624-6906, website: - Terne II discussed at [1]
  • Gerard Roofing Technologies, website:
    Modular metal shake and tile panels with granular coating
  • Met-Tile, website:
    Modular metal roof-tile panels
  • Atas International, website:
    Modular metal shingle, tile, and standing-seam panels
  • Custom-Bilt Metals, website:
    Modular metal shakes and standing seam panels

-- Adapted with permission from Best Practices Guide to Residential Construction.

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