The most frequently replaced exterior building component is the roof system, and roof system replacement costs are rising. As a result, building owners want to make informed choices to maximize their investments. Choosing a roof system with a projected long service life will help achieve this goal.
NRCA realizes this issue is important, but applying life-cycle cost concepts to roofing decisions is difficult. There is a lack of accurate data and numerous subjective variables to consider. Life-cycle cost data typically are based on equations involving variables such as initial costs, maintenance costs, energy consumption, expected service life, and tear-off and disposal costs. Furthermore, to the best of NRCA's knowledge, there is no reliable, unbiased accumulation of data that establishes the service lives of various low- or steep-slope roof systems.
What's available
To assist life-cycle cost data seekers, there are several sources of roofing-related life-cycle cost information. NRCA does not endorse these sources; they are referenced for informational purposes only.
The most current life-cycle cost information can be found in two papers presented at the 21st RCI International Convention held in 2005. The late Carl Cash, former RCI Inc. member and senior principal at Simpson, Gumpertz & Heger Inc., Waltham, Mass., presented "2005 Roofing Industry Durability and Cost Survey," his third in a series of durability surveys. For this study, Cash indicated the response rate was low compared with the response rate to his previous studies. He theorized the low response rate was because all roof systems are perceived as equal. Cash commented that, in comparison with his previous studies, respondents appeared to be more optimistic regarding how long roof systems should last.
The second paper, "Equivalent Uniform Annual Cost (EUAC): A New Approach to Life Cycle Analysis," was presented by James Hoff, Indianapolis-based Firestone Building Products Co.'s former vice president of technology and product development. His method expresses life-cycle cost as an annual cash-flow estimate instead of a lump-sum estimate of present value. According to Hoff, this method allows roofing professionals to compare the economic values of low-slope roof systems with different service lives. Hoff observes that comparing roof systems "in terms of EUAC may indicate that no single system offers an unassailable economic advantage."
Two conference papers presented at the 1997 Fourth International Symposium on Roofing Technology also addressed the issue.
The first paper, "The relative durability of low-slope roofing," was Cash's second durability study. For this study, Cash sent out 4,200 questionnaires, and about 10 percent of the questionnaires were returned. Based on these responses, Cash concluded durability is not one value but a range of values for each roof system.
The other paper was written by Kenneth G. Schneider Jr. and Anne S. Keenan, both formerly of the Roofing Communications Network in Charleston, S.C. They reported on the performances of nearly 22,000 roof systems in "A documented historical performance of roofing assemblies in the United States 1975-1996." The study's purpose was to continually average the actual historical life spans of roof system types to provide a mean service life. The authors indicated they would continue to collect data and maintain the database; however, NRCA is unaware of any updates.
To determine life-cycle cost data on your own, you can reference ASTM E917-05, "Standard Practice for Measuring Life-Cycle Costs of Buildings and Building Systems." It is a method that measures—in present-value and annual-value terms—the sum of all relevant costs associated with owning and operating a building or building system during a specified time period. It can be adapted for roofing, but it may be too complicated for some users to implement.
What's next
It has become apparent it is getting more difficult to find people who will conduct and participate in life-cycle cost surveys. NRCA encourages the roofing industry to develop meaningful methods to assist with collecting life-cycle cost data.
Joan P. Crowe, AIA, is an NRCA director of technical services.
COMMENTS
Be the first to comment. Please log in to leave a comment.