Challenging economic conditions have heightened interest in long-term roofing systems. As a result, life cycle costing considerations are playing a more significant role in roof specifications.
Choosing a roofing system based on long-term performance can mean a higher installed cost. However, longer-lasting systems have proven to cost less over time because they are more durable and require less maintenance. Additionally, such roofing can lead to energy savings over the roof's life, depending on system design, facility type, location and other conditions.
More building professionals recognize the value of investing in 20- or even 30-year roofing solutions. At the same time, there is a growing preference for thicker, more durable roofing systems featuring 60-, 80- and 90-mil membranes.
Life cycle cost
Over the years, various roofing industry professionals have introduced data suggesting that certain roofing systems offer a better life cycle cost than others. Although life cycle costing is a valuable economic tool, the range of variables involved complicates accurate calculations.
Expected service life
In a study of more than 25,000 roofing systems in use between 1975 and 1996, Schneider and Keenan1 calculated the average service life for a variety of roofing styles (see Figure 1).
Average service life in years
Figure 1. Major categories of low-slope commercial roofing systems performed in a fairly narrow range, according to a study of more than 25,000 roofing systems in use between 1975 and 1996.
The study found that the useful lives of major classes of low-slope commercial roofing systems cluster in a fairly narrow range. Most systems lasted between 16.8 and 18.4 years, with the exception of asphalt BUR (13.6 years) and PVC systems (9.5 years). However, Schneider and Keenan observed that premature failures of two-ply systems installed in the early 1970s might have shortened the average service life of asphalt BUR. Also, the high number of premature failures of unreinforced PVC membranes installed in the mid-to-late 1970s noticeably affected the average PVC service life.
Because manufacturers no longer sell these products, most roofing systems installed today should provide close to 20 years of useful working life, assuming that the roofing system is installed by a trained, experienced roofing professional.
Maintenance adds years to service life
Proper maintenance can extend the life of some roofing systems beyond 20 years. In fact, 30-year warranties are now available for single-ply EPDM roofing systems as these systems have a proven track record of long-term success.
Although Schneider and Keenan didn't examine the effects of maintenance, it's believed that roofs with longer-than-average service lives received professional maintenance regularly. Accordingly, the cost of maintenance must be included in any life cycle cost calculation. However, this cost may be offset by an increased overall service life.
It's also possible that the differences in service life mirror the ease of maintenance for different roof systems. For example, the gravel surfacing of asphalt BURs can complicate locating and repairing minor flaws, which accounts for the relatively low average service life that Schneider and Keenan discovered for these systems. On the other hand, the relative ease of inspecting and repairing a more-accessible membrane surface explains the longer average service life for modified bitumen and EPDM roofing systems.
Many owners and managers also recognize that new roofing products can minimize annual maintenance expenses. Increased interest in more durable roofing systems may be driven by concerns about weather-related rooftop damage and more realistic expectations of the effect of service traffic on roofs.
For example, 90-mil EPDM roofing systems offer more resilient thickness and protect against natural weathering and service traffic for the periodic maintenance of rooftop equipment. When assembled with polyiso insulation that is factory-applied to strand board, these roofing systems can protect against incidental punctures, 100-mph winds and two-inch hailstones. In addition to extended service life, this type of roofing system can offer a lower annualized cost than 45- and 60-mil EPDM, two-ply modified bitumen, four-ply BUR, and 45- and 80-mil TPO membranes.
Avoid overestimating your investment horizon
Determining whether service life should, or will, reach or exceed 20 years requires in-depth analysis. It's quite possible that, two decades from now, roof systems may be required to do more than keep water out of buildings. A roof installed today could be serviceable in 20 years, but might need to be replaced anyway to make way for new standards and technologies. For example, photovoltaics may turn future roofing systems into miniature electric power stations. Likewise, growing interest in "green roofing" may turn roofs into grasslands and gardens.
Know the time value of money
Most canned life cycle cost calculations either assume a relatively low inflation factor, typically three or four percent, or measure cost in constant dollars. However, the real cost can be calculated only by determining the opportunity cost of money.
In the case of a manufacturing company, the real cost of a dollar spent on roofing must be measured in terms of what return the same dollar could bring if it was invested in manufacturing equipment or other capital. In the end, the real cost of money exceeds the inflation rate.
Consequently, the time value of money places a higher premium on the initial installed cost than originally expected. For example, the future worth of the $10,000 initial cost for a 20-year roofing system is $73,000 when discounted at 10 percent, $197,000 at 15 percent, and $528,000 at 20 percent.
Studies and industry research are as important for accurate life cycle costing as is consulting a qualified, professional roofing contractor. Many contractors maintain databases to track the performance of the systems they install. Armed with information on similar sized or larger roofing systems, local contractors can offer insights to help determine what system would work best in each situation and what service to expect. In addition, these professionals can provide information on realistic maintenance costs that will help protect the initial investment.
There are neither simple equations nor quick, sure-fire ways to calculate the exact roofing life cycle cost. An accurate estimate includes many factors, such as the time value of money and the expected investment horizon, which only an individual building owner can determine. Selecting products from a reputable manufacturer with a proven track record of performance, the ability to provide technical guidance, and a sound financial history is an essential first step. However, quality workmanship and professional maintenance affect the service life more than the system type itself.
Most important, hire only experienced professional roofing contractors who are familiar with local conditions. Their first-hand knowledge is an outstanding resource for determining accurate installation costs and costs for the maintenance essential for keeping the system performing well over the long haul.
James Hoff is vice president of marketing for Firestone Building Products Co. in Carmel, Ind. He can be reached at HoffJames@firestonebp.com and 800-428-4442.
1 Schneider, K. G., and Keenan, A. S. (1997). A documented historical performance of roofing assemblies in the United States: 1975-1996. Proceedings of the Fourth International Symposium on Roofing Technology (pp. 132-137). Rosemont, Ill.: National Roofing Contractors Association.