Retrofit Roofing with GALVALUME Standing-seam Roof Panels

The 10 roof locations, indicating the average pH of the precipitation across the U.S.Figure 1: The 10 roof locations, indicating the average pH of the precipitation across the U.S.

A Study Demonstrates GALVALUME Provides Sustainable Value for the Life of a Building

Buildings account for 40 percent of our nation’s energy consumption and almost 75 percent of the electricity used in the country. According to the Washington, D.C.-based Nuclear Energy Institute, energy consumption is expected to grow 1.1 percent annually. By 2030 our nation’s electricity demands will be 45 percent greater than today. Many people neglect to recognize the cheapest and most reliable source of energy is the energy we don’t use. Saving energy through energy efficiencies and sustainability is important to our nation’s future. Fortunately, retrofitting with metal roofing can help buildings conserve energy. GALVALUME-coated steel, a 55 percent aluminum-zinc alloy coated steel product, is a significant part of the larger family of metal roofing products.

The U.S. Department of Energy, Washington, estimates that in an average building, about one-third of the energy used is for cooling and heating of some sort. Of that cooling/heating energy, about one-half is attributed to the solar heat gain and heat loss at the roof. Yet, with today’s building stock, the roof is often the least energy-efficient component of the building.

Cool metal roofing can help. A cool metal roof has a high solar reflectance that keeps the surface relatively cooler than conventional roofing. GALVALUME roofing has a high solar reflectance when used unpainted. With cool pigmented paint systems applied to GALVALUME roofing, the solar reflectance and thermal emittance can be high, which is the ideal cool roof in climates where cooling dominates.

GALVALUME-coated Steel

According to the Washington-based U.S. Environmental Protection Agency, “Sustainability is important to making sure that we have and will continue to have, the water, materials, and resources to protect human health and our environment.” The use of GALVALUME sheet as a metal roofing product provides sustainability in a number of categories.

The strength, durability and longevity of the product help to minimize the replacement schedule, which lowers the environmental impact of replacing the product with virgin material. The GALVALUME sheet steel product has as a minimum 25 percent recycled content and at the end of its useful service life, it is fully recyclable. These features help to keep metal roofing, like GALVALUME sheet, out of landfills.

Retrofitting with GALVALUME roofing creates opportunities for improving the energy efficiency of the roof system. By adding more insulation or a radiant barrier or solar-thermal heating systems or even photovoltaics, a GALVALUME retrofit roof often helps lower the environmental burden of the building and reduce cooling and heating energy. According to the results of a metal roofing industry study, these benefits are predicted to last for the life of the building itself because of the excellent projected service life of the GALVALUME-coated steel product.

Long-term Durability

The 10 roof locations, indicating the average pH of the precipitation across the U.S.

Figure 1: The 10 roof locations, indicating the average pH of the precipitation across the U.S.

In a study sponsored by the Zinc-Aluminum Coaters Association and the Glenview, Ill-based Metal Construction Association, a novel inspection and durability analysis protocol, published in the Journal of ASTM International in September 2011, was used to evaluate 10 unpainted GALVALUME low-slope standing-seam roof (SSR) systems ranging in age from 20 to 35 years and located in four U.S. climate zones. Although the full report predicting the service life of the total roof system is still in preparation, the results for the GALVALUME SSR panels themselves on these 10 roofs are reported within this article. The results provide clear evidence of the superior long-term durability of GALVALUME SSR panels. As such, they produce a significant beneficial impact on the calculations used for green-building rating systems and life-cycle analyses for newly built and retrofit roofing applications.

Figure 1 shows the 10 roof locations on a map indicating the average pH of the precipitation across the U.S. Lower pH values indicate more corrosive, acidic rainfall. The 1999 map represents a mid-way point of precipitation pH improvement for the roof inspection sites between the late 1970s and today. With the exception of one 20-year-old roof, the roof age ranged from 29 to 35 years.

Using a portable magnetic induction instrument, GALVALUME coating thicknesses were measured on a number of panels to select a representative panel for sampling. The amount of corrosion that had occurred was then determined by analyzing samples removed from one of the panels. The technique involved disassembling the end lap and removing a piece of the roof from an area that was exposed to the environment and from the adjacent overlapped area, which was effectively protected from the environment. The technique is shown in the mock-up SSR, Figure 2.

About the Author

Ron Dutton, Scott Kriner, Chuck Howard
Ron Dutton is president of Ron Dutton Consulting Services. He provides technical services for new product development, field failure analysis and product training for the metal construction and appliance industries. Ron has 40 years of experience in the areas of metallic-coated and prepainted steel products, with a strong emphasis on 55 percent A1-Zn alloy coated sheet. Scott Kriner, LEED AP O+M, is president of Green Metal Consulting Inc. He is serving the Metal Construction Association as technical director. He is also consulting for manufacturers and suppliers of metal roofing and wall systems. Chuck Howard, P.E., has been designing, building and consulting about the use of metal in new and retrofit markets since the 1970s. In his presentations, Chuck speaks from his education as an engineer, his experience as a contractor and his background as an author and speaker about the subject of retrofit. He has been associated with nearly 30 million square feet of metal roofs and has been making metal roof presentations for more than 25 years.

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