EPDM ROOF SYSTEM PERFORMANCE:
AN UPDATE OF HISTORICAL MAINTENANCE COSTS
James L. Hoff
This paper provides a five-year update of the article “EPDM Re-Roofing versus Re-Cover: A
Comparison of Historical Maintenance Costs” originally published in RCI Interface , July, 1998.
One of the most important steps in designing a roof involves selecting the specific type of roof system best suited for specific building conditions and building owner needs. In order to make the optimal selection, the designer must evaluate the costs and benefits of the many system options available. While initial costs of roofing systems can be calculated with reasonable accuracy, it is much more difficult to accurately calculate the longer-term maintenance costs for different roofing systems. In order to make the best decision, the designer needs statistically accurate and reliable information based on actual historical performance of roofing systems.
The warranty service records of roofing manufacturers offer an interesting opportunity to expand the industry's understanding of roof system performance. Because warranty records typically include thousands of roofs covering millions of square feet, an analysis of the information contained in these records may be more statistically reliable than information gathered from limited sources. Because warranty service records also identify when a roof was installed and
when warranty maintenance was performed, they can provide an accurate chronology of roof performance. Finally, because warranty records provide the actual cost of any roof maintenance performed, roof performance can be analyzed from an economic persective.
THE ROOF SERVICE DATA BASE:
The data base used in this study is significant both in size and scope. In regard to size, the data base covers over three billion square feet of EPDM roofs installed on over one-hundred-fifty thousand roofs from 1982 to the present. Regarding the scope of detail provided in the data base, the file for each roof contains extensive background information, including:
1. Construction Type (New Construction / Re-Roof / Re-Cover)
2. System Type (Ballasted / Adhered / Mechanically Attached)
3. Geographic Location (City / State or Province)
4. Installing Contractor (Identification & Current License Status)
5. Warranty Information (Date Completed / Warranty Term)
Because all roofs in the data base received a material and workmanship warranty, the data base also contains detailed information regarding the timing, cost and type of maintenance performed or authorized by the manufacturer during the warranty period. The typical warranty period of the majority of roofs in the data base is ten years, and the service records for each roof in the data base identify the cost and date of all maintenance expenditures made by the manufacturer during this period. These expenditures include both the costs of emergency leak calls as well as costs for more comprehensive repairs when necessary. In addition, each maintenance activity is "coded" based on the principle roof system component that required maintenance, allowing for a detailed analysis of the causes of maintenance expense.
Given the level of detail available in the data base, a number of trends can be analyzed, including the relative performance of roofs over time, the average frequency and timing of maintenance activities, and the comparative performance of different roof systems, components and construction types.
DEFINITIONS AND METHODOLOGY:
1. Historical maintenance cost is defined as the manufacturer's actual recorded spending during
a specified period of service. For this study, costs are expressed as actual spending during
each year of roof service following the initial installation.
2. Maintenance costs for any given segment of the data base are divided by the total installed
surface area of that segment, in order to allow for comparison between different segments
of the data base. As a consequence, the annual unit maintenance costs for roofs installed in
any year can be compared to the unit costs for roofs installed in any other year. 3. In order to adjust for inflation, spending is stated in constant units, using 1982 as base year
and adjusting each year based on the U.S. National GDP Deflator as calculated by the United
States Bureau Of Labor Statistics.
4. In order to maintain the confidentiality of the manufacturer’s actual dollar costs in the data
base, maintenance costs are indexed against a baseline year.
EPDM ROOF SYSTEM PERFORMANCE: HISTORICAL TRENDS
Overall EPDM Maintenance Cost Trends At least ten years of actual historical maintenance
costs are now available for all roofs installed in 1993 or earlier. Chart 1 illustrates the overall change in maintenance spending during the first ten years of service for EPDM roofs installed each year from 1982 to 1993. As illustrated by the chart, unit maintenance costs declined 85% from 1982 to 1987. As will be discussed later in this paper, the significant drop in costs is most
likely attributable to changes in product technology introduced during those years. Although the improvement trend begins to flatten out slightly from 1987 through 1993, cost reductions continue each year; and even these smaller incremental improvements account for another 60% reduction in maintenance cost.
It should be noted that when this study was first published in 1998, complete historical data was available only for the first five years of service for many of these roofs. As a consequence, the ten-year maintenance costs were estimated by applying regression analysis to the five-year trend available at that time. Five years later, it is very gratifying to report that the actual ten-year trends indeed follow the 1998 prediction. In order to demonstrate the closeness between the 1998 projections and actual results today, a line indicating the original projection has been added to Chart 1. It should be noted that any slight differences in the projected and actual cost are statistically insignificant at a 99.5% level of reliability.
Maintenance Costs by Component Chart 2 provides a breakdown of ten-year costs by the type of
component requiring maintenance. For this study, components were divided into three broad categories: 1) field seams, 2) perimeter flashings, such as base tie-ins, edge metal flashings and
terminations, and 3) other components, including curbs, penetrations and membrane attachment.
During the period from 1982 to 1993, maintenance costs for both field seams and perimeter flashings improved significantly. The trends in this chart appear to reinforce the commonly held opinion that much of the improvement in EPDM system performance is due to changes in seaming and attachment technology. Costs associated with field seams and perimeter flashings have declined 92% and 95%, respectively. It should be noted that this improvement coincides with the introduction of several important component technologies by the roofing manufacturer:
Year Introduced: Technology:
1985-1986 Butyl-based splice adhesive replaces neoprene-based adhesive
1985 - 1986 EPDM-based wall flashings replace neoprene-based flashings
1987 - 1988 Tape laminates replace adhesive seams at roof edges and battens
1988 - 1989 Metal battens and screw fasteners replace wood nailers and nails
1991 - 1992 Reinforced perimeter fastening strips introduced
1992 - 1993 Seam tape with high-solids primer replace adhesive seams
Maintenance Costs by System Type Chart 3 provides a breakdown of ten-year costs by type of
EPDM roof system. For this study, EPDM systems are divided into three major categories: 1) ballasted, 2) fully adhered, and 3) mechanically attached. The chart clearly illustrates that the relative performance of these three basic system types has also changed significantly over time. While both mechanically attached and fully adhered roofs under-performed ballasted roofs in the early years of the data base, all three systems now provide almost identical performance. This performance undoubtedly is related to previously identified improvements in field seams as well as the relative number of seams required for each of these systems. While ballasted roofing systems typically use EPDM membrane panels up to 50 feet wide by 100 feet long, fully adhered and mechanically attached systems frequently use smaller roof panels requiring more field seams. Given the relatively high maintenance costs associated with field seams in the early years of the data base, it is reasonable to infer that roofs with a large number of field seams will be affected the most by seam performance. As the performance of field seams has improved, however, the number of seams in the roofing system has become a less critical factor, thus narrowing differences in system performance.
Ten-Year Maintenance Costs versus Initial Installed Costs Although the cost indexing employed
in this study allows for comparison of maintenance costs over time, this indexing provides no immediate comparison to the initial cost of the roof. However, using a similar indexing approach, the estimated initial cost of the roofs in the data base can be compared to the actual 10-year maintenance costs. Based on cost data derived from a nationally published construction cost
estimating workbook, indexed installation costs were calculated for several types of EPDM
1systems in the data base. As illustrated in Chart 4, ten-year maintenance costs for EPDM roofing systems account for a very small percentage of total roof costs, even for systems installed in the early 1980s. While 10-year maintenance costs for EPDM roofs installed in 1982 amounted to less than 10% of the original installed cost, the same ten-year maintenance costs for EPDM roofs installed in 1993 is barely more than 1% of the original installed cost.
EPDM Re-cover versus Re-Roofing One of the most important steps in designing a roofing
system for an existing building involves the evaluation of the existing roof. Even before the specification for a new roof system can be developed, the designer must first decide whether to remove or retain the existing roof. Although it is generally acknowledged that the removal of the existing roof system is the most conservative design practice, environmental and economic concerns make complete roof tear-off increasingly difficult. Before deciding whether to tear off the existing roof, the designer must analyze the costs and benefits of complete removal.
Chart 5 shows the ten-year performance trend for two approaches to roof replacement: 1) re-roof,
or the tear-off of the existing roof and installation of a new roof, and 2) re-cover, or the
installation of a new roof directly over the existing roof. For comparison purposes, the chart also provides similar information for roofs incorporated into new construction work. Although the ten-year maintenance costs for new construction and re-roofing projects installed during the early 1980s were almost equal, the costs of re-cover projects in the early 1980's were significantly higher than either new construction or re-roof maintenance costs. However, this difference in costs narrows each year. In fact, by 1988, the gap in maintenance cost between re-cover and re-roofing has virtually disappeared. In fact, for roofs installed between 1988 and 1993, the difference in ten-year repair costs between EPDM re-cover and re-roofing is statistically insignificant.
What caused the performance difference between EPDM re-roofing and re-cover in the early 1980s, and why did this gap close so dramatically by the end of the decade? In order to better understand this trend, we must look back at the performance trends of the basic design and material components of EPDM roofing systems. Although improvements in components such as field seams and perimeter attachments obviously reduced maintenance costs for both re-roofing and re-cover, it would appear the effect on re-cover applications has been more favorable. Undoubtedly much of this improvement can be attributed to the elimination of neoprene-based seam adhesives, which were commonly recognized to be more sensitive to moisture drive than butyl- or EPDM-based adhesives and seam tapes. Assuming a typical re-cover project installed over an existing roof may contain more latent moisture than a roof installed over a complete tear-off, improvement in the moisture resistance of any component will obviuosly contribute to lower maintenance costs. Improvements in perimeter securement also may have contributed to the relative improvement of re-cover systems, since attachment to hidden substrates, which is typical practice for re-cover projects, is obviously more difficult than attachment to substrates which have been fully exposed by the removal of an existing roof.
EPDM ROOF SYSTEM PERFORMANCE: SUMMARY OF FINDINGS
Based on the maintenance records of the three billion square feet of EPDM roofs in this study, EPDM roofing performance has improved dramatically over the past 20 years. In fact, the improvement in performance now makes the cost of maintaining an EPDM roof for ten years almost negligible. Given the extremely low cost of maintenance through the first ten years of service, it is also likely that the great majority of these roofs will continue to offer superior service for many years beyond the ten years of this study.
It also appears this improvement has been most significant for EPDM systems used as re-covers over existing roofs. Given the escalating costs associated with roof tear-off and the ever-present
financial constraints on building owners, a roofing designer certainly can take comfort knowing that a properly selected EPDM re-cover system may provide an acceptable service life at a reasonable cost. Of course, the data presented in this article should not be used to endorse re-covers in all situations. Existing roofs that are saturated with water or seriously deteriorated are obviously candidates for a complete tear-off. However, the data in this study clearly suggests that, when an EPDM re-cover system is properly installed over a suitable existing roof, it will provide many years of acceptable service with minimal maintenance expense.
1. Installed cost data derived from 2002 National Construction Estimator (Craftsman
Books). Installed cost is based on the application of a ten-year warranted EPDM roofing system installed over an exposed metal or concrete roof deck and a minimum R20 polyisocyanurate roof insulation. Indexed unit costs are adjusted for inflation during the period of 1982 through 1993 based on the U.S. National GDP Deflator as published by the United States Bureau Of Labor Statistics. Indexed unit costs are available only for ballasted and fully adhered systems. Because mechanically attached EPDM systems may vary significantly in system design, it was not possible to develop a reliable unit cost using the general system descriptions in the National Construction Estimator.
Jim Hoff (firstname.lastname@example.org) has served in a variety of technical and management roles in
the construction industry for over twenty-five years. Currently, Mr. Hoff is Vice President of Marketing for Firestone Building Products Company and serves as Chairman of the Board of the Polyisocyanurate Insulation Manufacturers Association. Mr. Hoff received an A.A.S. in architectural technology from Indiana Vocational Technical College, a B.A. in psychology from Indiana University, a M.S. in management from Indiana Wesleyan University, and currently is completing his doctoral dissertation for a D.B.A. in management from the University of Sarasota.