Quantitatively Assessing the Service Life of 55 % Aluminum-Zinc Alloy-Coated Steel Standing Seam Roof Systems

Abstract

At the Seventh Symposium on Roofing Research and Standards Development, a new, quantitative method for evaluating service life of a single 55 % aluminum-zinc (Al-Zn) alloy-coated steel low-slope standing seam roof (SSR) system was presented and subsequently published. Using samples from a roof in Denver, CO, the authors utilized laboratory corrosion analysis, together with a visual roof inspection protocol, to predict the total roof service life of a similarly constructed roof when built using today's best practices. In this paper, the authors describe the use of this unique method to further evaluate the total service life of an additional 13 roofs in five different climate zones across the United States, enabling conclusive service life projections based upon empirical data. The site inspections and testing analyzed all critical roof system components. Evaluation methods and protocols set forth criteria for evaluation of the total roof system, including base materials and all ancillary components bearing on total roof system performance and integrity. Included in this analysis is the long-term field performance of butyl sealants in place for up to 35 years. Methods are established to evaluate practical and economic viabilities of capital repair versus replacement following common sense criteria. Definitions are posed for terms such as “end-of-life” and “best practice.” Results confirm the validity of this method and conservatively project total roof service life in excess of 60 years for such roofs if installed today in a wide range of environments using today's best practices. Thus a properly installed 55 % Al-Zn alloy-coated steel SSR system does not require replacement during the building's entire service life of 60 years as established by the Leadership in Energy and Environmental Design (LEED) program (v4).