By Gary Kassem
For several years, manufacturers of white or light-colored roof membranes have extolled the energy-related, solar reflection benefits of their product as an indisputable advantage. Frankly, the answer isn’t the solely black-and-white conclusion those manufacturers would have you believe.
While it’s true that white or lighter-colored membranes reflect infrared heat away from the roofing surface, color is only one factor in an otherwise complex combination of natural and man-made dynamics affecting a roof’s performance, energy-efficiency, durability, and, ultimately, its overall cost to own and maintain.
Basing your decision solely on color – which admittedly no one does – is a sure-shot way to achieve less-than-acceptable performance. Numerous factors should be evaluated before making any selection of roofing materials and workmanship. Factors such as heating vs. cooling days; cloud cover; energy costs; long-term color retention; and rooftop maintenance are significant determinants in whether your ultimate roofing decision will lead to savings or loss.
Research is under way to find mathematical models to adequately answer such questions. For now, however, old-fashioned common sense remains your best guide.
What’s the True Goal of a Roof?
Answer: To remain leak-free for as long as possible.
Color retention and surface texture are two important factors that relate to solar reflectance – the amount of solar radiation reflected away from the roof surface. Since solar radiation is responsible for heat, it is an important value to consider. But how often does the roofing material you see in a sales presentation compare to the actual color of the roof after exposure to the elements? Does the membrane collect pollution? Does it permit biological growth? Does the fastening method or installation technique allow plain old dirt and dust to accumulate? Are any materials regularly exhausted onto the roof surface from inside the building or by rooftop equipment? Finally, how often must such a membrane be washed – and at what expense – to maintain a color that is even close to that of the new material?
If those weren’t apparent questions to ask before, they should be now.
The fact is, all roofing membranes change color after installation. In the case of white membranes, the color may darken, resulting in lower solar reflectance as the membrane ages and becomes discolored. This discoloration and aging may also lead to overheating of the roofing formulation, weakening and physically damaging the roof over time. Conversely, EPDM is formulated to craze and naturally lightens to a grayish color over time, leading to slightly better solar reflectance – a significant side benefit worth noting in any discussion on solar reflectance.
One way manufacturers of white membranes try to keep the color constant is by formulating products that “chalk” or release fillers onto the roof surface. Typically, an element such as titanium dioxide is incorporated. This filler material exudes to the surface of the membrane, dislodging any foreign objects that are stuck to the surface. The membrane is then washed, or simply allowed to drain from natural rainfall.
The down side of this entire approach is that fillers that contribute to the compound quality of the exposed membrane may be washed away, resulting in possible loss of thickness, surface deterioration (such as cracking or exposure to the reinforcement scrim), changes in the physical properties of the overall roofing formulation, and more.
It’s a fact of life: Everyday materials are going to be installed on rooftops. Harmful substances range from dust, dirt, and pollution (from auto and carbon-related emissions) to biological growth that either takes root in collected dirt or attaches itself directly to the membrane. If aggressive, regular countering measures are not taken, these materials will become embedded in the membrane surface in a way that resists rainfall erosion and promotes discoloration. Thus, solar reflectance may be decreased, as are the associated energy savings.
The smartest, most efficient and proven way to save on your roof’s energy costs and your long-term cost of ownership is by selecting the right combination of membrane, insulation, and installation workmanship up front.
In fact, insulation is the best understood method of controlling energy loss. Today’s range of insulating materials are well-understood, well-documented in their efficacy, and are not subject to things like solar reflectance, dust, and dirt.
While it’s true that R-values of insulations may change over time, extensive research and documentation have led to aged values for the various products available. Industry organizations such as the National Roofing Contractors Association (NRCA) suggest the use of insulation as a reliable, long-term method of controlling energy consumption.
Comparing Reflective Roofing vs. Insulated Less-Reflective Roofing
According to the Oak Ridge National Laboratory Roof Radiation Control Calculator, using reflective roofs alone in Northern United States may actually increase energy costs by decreasing solar heat gain in winter months.
Non-reflective roofs can be made to be just as energy-efficient as a reflective roof simply by adding roof insulation; in many areas of the United States, a minimal amount of insulation (often as little as a factor of R-1) is needed to offset a heat-reflective coating.
Note: The calculated energy savings for reflective roofs assume that the reflective roof will be cleaned periodically to maintain optimum solar reflectivity. Lack of periodic cleaning may reduce energy savings over time.
Long-term considerations should rule any common sense evaluation of performance expectations and costs. This is especially true when you consider the long-term cost implications of a major expense like a roof. With that in mind, perhaps the greatest attention should be paid to the life expectancy of the roof membrane itself.
When you evaluate factors such as weathering performance and tensile strength, EPDM continues to be a material for building owners who have an eye on both the long-term viability of their roof and the bottom line.
To be reliable, the life-cycle costs of your roof must incorporate the expected life of the roofing membrane, not just whether the membrane will provide negligible savings over a 10- or 20-year period if it stays white.
According to the Laboratory Evaluation of EPDM Roof Membrane: A 17-year History of Performance reported at the International Symposium on Roofing Technology, over time, “EPDM’s physical properties show a general increase in tensile strength, tear resistance, and hardness.” The study also states that “it may require more than 50 years of exposure [to the elements] to drop below MRCA ME-20 performance requirements.”
What is the “best” way to evaluate the long-term value of any roof? Locate and deal with a manufacturer that promises to stand behind its product with a long-term warranty, a proven history of performance, and a real-world look at the energy efficiency of the product. Today, more than ever before, it is wise to make investments that are based on sound principles.
Remember, your best investment is one that:
• Involves a membrane product that stands the test of time.
• Combines insulation materials that match your specific needs and performance expectations.
• Is professionally installed with a roofing system that has similarly been tested, proved, and warranted to provide long-term durability and reliability.
Such a combination is a real winner for any building owner.
Gary Kassem is president at SingleSource Roofing Corp. (www.singlesourceroofing.com), Pittsburgh.