Galvalume-coated Metal Roofs Will Last at Least 60 Years with Minimal Component Repair

The term “infrastructure sustainability” continues to gain importance because of rapidly increasing building infrastructure components around the country needing major repairs and/ or replacements. Consequently, roof maintenance or replacement materials and methods must last at least 60 years; consider LEED v4 from the Washington, D.C.-based U.S. Green Building Council. For more than 30 years, millions of square feet of Galvalume-coated roofs have resisted the atmospheric conditions to which they are exposed with little or no maintenance and are well prepared to continue protecting building interiors for more than 30 additional years. Material science and professional project engineering and installation prove Galvalume-coated metal standing-seam roofs will perform for that period of time.

This is a nine-year-old painted Galvalume roof in Alabama.

This is a nine-year-old painted Galvalume roof in Alabama.


The first standing-seam metal roof was introduced by Armco Steel Corp., Middletown, Ohio, at the 1932 World’s Fair in Chicago. Armco Steel ceased doing business many years ago, but its standing-seam metal roof design has been adopted by all manufacturers in today’s commercial metal roofing market. The second longest-lasting introduction into this market was in the early 1970s when Bethlehem, Pa.-based Bethlehem Steel introduced a Zinc/Aluminum coating—now known as Galvalume—for carbon-steel metal roofs. This coating, applied to both sides of the steel coil, has been successfully used for the majority of metal standing-seam roofs ever since.

Since Galvalume was introduced, there have been several evaluations, reports and predictions as to how this product would “weather” the test of time. In 2012, the Chicago-based Metal Construction Association (MCA) and Olympia, Wash.-based Zinc Aluminum Coaters Association (ZAC) commissioned a study to perform forensic tests at 14 existing Galvalume standing-seam metal roof sites throughout the country in varying climates and precipitation pH. The average age of these roofs was more than 30 years at the time of testing.

Initially, the sites were selected based on temperature and humidity zones throughout the U.S. As the field results were processed, however, it became apparent the expected lives of these roofs were directly dependent on the precipitation pH levels with very little correlation to temperature and humidity. The building sites chosen were located in the following states:

  • Massachusetts (2 sites)
    This Galvalume roof in Missouri is nine years old.

    This Galvalume roof in Missouri is nine-years old.

    Ohio (3 sites)
    South Carolina (2 sites)
    Georgia (1 site)
    Colorado (1 site)
    New Mexico (1 site)
    Arizona (1 site)
    Oregon (1 site)
    Wyoming (2 sites)

The study was directed by MCA and three independent consultants and their firms, which managed and performed the field work: Rob Haddock of Metal Roof Advisory Group, Colorado Springs, Colo.; Ron Dutton of Ron Dutton Consulting Services LLC, Annapolis, Md.; and me and my firm Metal Roof Consultants Inc., Cary, N.C. This group, plus Scott Kriner, MCA’s technical director, authored the actual report, which was issued by MCA and ZAC in November 2014 and is available online.

The team harvested and analyzed actual field samples of Galvalume-coated metal standing-seam roof panel materials and sealants and examined all the individual roofs’ ancillary components. Finally, it created an experienced assessment of the roofs’ conditions and associated costs to replace.


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Attention Roof System Designers: Numerous Roof Components Work Together to Affect a Building

There has been a great deal of opinion expressed in the past 15 years related to the roof cover(s), or the top surface of a roof system, such as “it can save you energy” and “it will reduce urban heat islands”. These opinions consequently have resulted in standards and code revisions that have had an extraordinary effect on the roofing industry.

The building type should influence the type of roof system designed. Some spaces, like this steel plant, are unconditioned, so insulation in the roof system is not desired.

The building type should influence the type of roof system designed. Some spaces, like this steel plant, are unconditioned, so insulation in the roof system is not desired.

Let’s say it loud and clear, “A single component, does not a roof make!”. Roofs are systems, composed of numerous components that work and interact together to affect the building in question. Regardless of your concern or goal—energy performance, urban heat-island minimization, long-term service life (in my opinion, the essence of sustainability) or protection from the elements—the performance is the result of an assembled set of roof system components.

Roof System Components

Energy conservation is an often-discussed potential of roofs, but many seem to think it is the result of only the roof-cover color. I think not. Energy performance is the result of many factors, including but not limited to:

Building use: Is the building an office, school, hospital, warehouse, fabrication facility, etc.? Each type of building use places different requirements on the roof system.

Spatial use and function be low the roof deck: It is not uncommon in urban areas to have mechanical rooms or interstitial spaces below the roof—spaces that require little to no heating or cooling. These spaces are typically unconditioned and unoccupied and receive no material benefit from the roof system in regard to energy savings.

Roof-deck type: The type of roof deck—whether steel; cast-in-place, precast and post-tensioned concrete; gypsum; cementitious wood fiber; or (don’t kill the messenger) plywood, which is a West Coast anomaly—affects air and moisture transport toward the exterior, as well as the type of roof system.

Roof-to-wall transition(s): The transition of the roofing to walls often results in unresolved design issues, as well as cavities that allow moisture and vapor transport.

Meanwhile others, like this indoor pool, require extreme care in design and should include a vapor retarder and insulation.

Meanwhile others, like this indoor pool, require extreme care in design and
should include a vapor retarder and insulation.

Roof air and/or vapor barrier: Its integration into the wall air barrier is very important. Failure to tie the two together creates a breach in the barrier.

Substrate board: Steel roof decks often require a substrate board to support the air and vapor barrier membranes. The substrate board also can be the first layer of the roof system to provide wind-uplift resistance.

Insulation type: Each insulation type—whether polyisocyanurate, expanded polystyrene, extruded polystyrene, wood fiber, foam glass or mineral wool—has differing R-values, some of which drop with time. Many insulation types have differing facer options and densities.

The number of insulation layers: This is very important! A single layer of insulation results in a high level of energy loss; 7 percent is the industry standard. When installing multiple layers of insulation, the joints should be offset from layer to layer to avoid vapor movement and thermal shorts.

Sealing: Voids between rooftop penetrations, adjacent board and the roof-edge perimeters can create large avenues for heat loss.

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