Retrofit Roofing with GALVALUME Standing-seam Roof Panels

Although the sample locations are shown as circular disks, the actual samples were much larger in size and rectangular in shape. After sampling, the end lap was subsequently reassembled with new butyl polymer tape sealants and supplemented with tube-grade butyl polymer as necessary to ensure a complete, weathertight seal on a new GALVALUME section.

The amount of corrosion that had occurred was then determined by analyzing samples removed from one of the panels.

Figure 2: The amount of corrosion that had occurred was then determined by analyzing samples removed from one of the panels.

Based on independent laboratory measurements, the corrosion rate in grams per square meter per year, or g/m2/yr, was calculated for each roof by dividing the amount of corrosion loss by the age of the roof. Using these corrosion rates, the projected panel service life can be calculated as the time required for total coating loss from the top surface caused by corrosion. This was done assuming the GALVALUME roof panels would be installed today with material ordered at a nominal coating mass of 165 g/m2 (AZ55), which is representative of most bare GALVALUME SSR systems today.

These projected panel service lives are plotted in Figure 3 against the precipitation pH values recorded near the respective building locations. Although these values vary as a function of local precipitation pH, they are, nevertheless, in good agreement with other studies, including “55% Al-Zn Alloy Coated Sheet Steel: The Versatile, Long Lasting Building Panel Steel,” Proceedings of the 5th International Conference on Zinc Coated Sheet Steel, 1997; “Atmospheric Corrosion Resistance of Skyward- and Groundward-Exposed Surfaces of Zinc- and 55% Al-Zn Alloy-Coated Steel Sheet,” Corrosion, Vol. 54 (7), 1998; and “Performance of 55% Al-Zn Coated Steel Sheets Used in Residential Houses in Australia,” Proceedings of the 4th International Conference on Zinc and Zinc Alloy Coated Steel Sheet, 1998.

The projected panel service lives are plotted against the precipitation pH values recorded near the respective building locations.

Figure 3: The projected panel service lives are plotted against the precipitation pH values recorded near the respective building locations.

The reference line at 60 years is significant in that it represents the “assumed building service life” in calculations of life-cycle analysis by the Athena Sustainable Materials Institute, Ottawa, Ontario, Canada. Thus, the data from this project support the proposition that a GALVALUME SSR system could be installed today on new or retrofit low-slope roof systems in a wide range of environments and not require replacement during the building’s entire service life. Of course, proper roof inspections and maintenance associated with roof ancillaries would still be required as they are with any other roof system. But the projected service lives demonstrated in the study demonstrate the sustainable benefits of using GALVALUME-coated SSR panels for new and retrofit applications.

Guidelines and Metal Roofing

Attention to reducing energy has resulted in many new codes and standards being introduced. One example is the International Code Council’s (ICC’s) International Green Construction Code, which is structured similarly to the voluntary LEED building rating program. Chapters about site sustainability, energy, materials and water are designed to limit the use of resources and energy while meeting the criteria in this code. The International Energy Conservation Code is another ICC code that is exclusively focused on energy usage in buildings. Under both these codes, a cool metal roof can help a building meet the ever-increasing stringent energy code.

In addition to codes and standards, there are many voluntary programs that rate buildings or create incentives for reducing energy. The most formidable green-building rating program is the U.S. Green Building Council’s LEED. Building projects that use metal roofing and metal components can qualify for many points in LEED, including a credit that is related to the impact of cool roofing on heat-island heating.

Energy Star is also a voluntary program that has a Roof Products Category. Energy Star identifies products that meet certain performance standards indicating they can contribute to reducing energy in a building. GALVALUME roofing can meet the criteria in Energy Star for solar reflectance in low- and steep-slope applications.

The explosion of so many codes, standards and incentive programs makes it almost impossible to know what is being enforced or offered in specific jurisdictions. To assist with that, the Building Codes Assistance Project (BCAP), Washington, is sharing information about the codes that have been adopted, contact information at the code offices, and demographics about construction activity and population in local and state jurisdictions on areas around the country.

An excellent reference for incentives available for renewable energy or energy-efficiency upgrades at the federal, state and local level is the Database of State Incentives for Renewable Energy (DSIRE), which is operated by the North Carolina Solar Center at N.C. State University, Raleigh, and Interstate Renewable Energy Council, Latham, N.Y., and funded by DOE.

In the area of energy reduction, the building construction industry is headed toward the ultimate in energy efficiency: net-zero-energy buildings. In fact, the Commercial Buildings Consortium was established in response to the Energy Independence Act of 2007. It is comprised of commercial building stakeholders working with the DOE to develop and deliver technology, policies and practices to ensure all new construction commercial buildings are net-zero energy by 2030 and all commercial buildings of any kind be net-zero energy by 2050.

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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