In this era of sustainable building practices and environmental conservation, the selection of roofing system for low-slope commercial buildings is often overlooked and undervalued.
There are many environmentally friendly roofing systems available, from dark-colored roofs that reduce heating costs in cold climates to reflective roofs that cool building temperatures in hot climates and roof gardens that decrease stormwater runoff. But when all the options are considered and factors are weighed, one roofing system seems to rise above the others when it comes to providing a complete sustainable package — ethylene propylene diene terpolymer, or EPDM.
As one of the few roofing membranes with more than 50 years of real-world experience, EPDM is unmatched when it comes to long-term service life. Thirty-year-aged EPDM has been known to exhibit physical properties that exceed those of new membranes. Tensile and tear strengths, as well as water absorption rates, have been demonstrated to meet or exceed present day specs for new membranes.
EPDM is available in both white and black options for different geographic climates. It’s commonly accepted that white EPDM saves energy by reducing air-conditioning usage, which is a major benefit in hot, southern climates. What is often overlooked is that black EPDM provides energy savings in cold, northern climates by reducing heating usage. A recent study by Ashley-McGraw Architects, PC and CDH Energy Corp analyzed various roofing system options in real-world conditions and concluded that in northern climates, dark-colored roofing is more energy efficient than white roofing and more cost effective when heating and cooling costs are examined.
The study found that the thermal heat loss of white roofing is 30 percent higher than that of black EPDM during the heating season, which means that it increases a building’s heating costs by more than 30 percent in northern climates when compared to black EPDM. In addition, the study found that the cooling cost savings from white roofing during the summer months does not outweigh this figure. The solar absorption of a dark-colored membrane is a valuable asset in northern climates, keeping a building warm during the winter months. The color of the roof membrane not only affects heating and cooling costs, it can also impact the environment; the additional heating burden from the use of a white membrane in a northern climate is thought to increase global warming due to consumption of more natural resources.
Another study, Life Cycle Inventory and Assessment of Low-Slope Roofing Systems in North America, examined roofing systems that used a variety of membranes, including EPDM-, TPO-, PVC- and SBS-modified bitumen. The study’s intent was to measure and compare the relative environmental impact of these differing low-slope roofing systems by creating a life cycle assessment (LCA), which is a scientific evaluation of the ecological aspects and potential effects of a product, process or service throughout its life cycle. This study’s LCA found that EPDM’s long-term environmental impact is much less than that of alternative roofing systems.
The study used the EPA’s Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI) model to account for all inputs associated with the manufacture and installation of the different roofing systems. The results suggested that one of the most meaningful measures for comparing the relative environmental impact of low-slope roofing systems is the global warming potential (GWP) related to their manufacture, installation and end-of-service-life disposition. The study held the service life constant at 15 years for all system types. The data showed that when compared to TPO-, PVC-, and SBS-modified bitumen systems, EPDM roof systems have the lowest global warming potential, smog impact and acid rain impact.
Stormwater management is a growing concern among building owners, particularly in large cities where stormwater and sewer systems are combined and sometimes unable to handle heavy rainfalls. In these settings, traditional ballasted systems can be modified to absorb and retain stormwater.
Dating back to the 1960s, ballasted EPDM roofs were the original sustainable roofs. This time-tested and reliable roof design still offers more sustainable features than most systems on the market today. A ballasted roof is one in which the roofing components are held in place using the natural weight of river-washed stones or pavers. Ballasted roofs are loose-laid, which means that the roofing materials, including the insulation and roofing membrane, are not fastened to one another or to the roof deck. Adjoining sheets of EPDM are spliced together, and the membrane and insulation are held down with ballast installed at a minimum of 10 pounds per square foot.
A ballasted EPDM roofing system can be easily upgraded to include stormwater retention components to help alleviate problems caused by excessive stormwater run-off. In many cities, a substantial rainstorm can overwhelm combined stormwater and sewer systems, causing raw sewage to be discharged into area waterways. In these settings, when a traditional ballasted system is modified, it can absorb and retain stormwater by adding drainage board and moisture-retention mats. This alteration allows the roofing system to retain as much as 67 percent of the water from a 24-hour rain event, providing substantial relief to public sewer systems.
Based on these findings, a dark-colored roofing system (for example, black EPDM) is an energy-efficient and cost-effective solution for buildings in cool climates. And when the additional benefits of EPDM, such as outstanding UV, hail resistance and the reduced likelihood of condensation issues, are evaluated, the selection of an EPDM roofing system in colder climates should be seriously considered.
Richard Stever is the environmental and energy-efficient solutions product manager for Carlisle Construction Materials in Carlisle, Pa.