Reflectivity: not just black or white question

On the surface, it might seem that the question of how reflective a roof membrane is could simply be a black and white issue. However, like most complex subjects, this one encompasses several important gray areas.

To better understand the subtle shadings surrounding any discussion on the reflectivity of roof membranes, SPRI recently sponsored an important three-year research program on reflectivity. SPRI, the organization representing sheet membrane and component suppliers to the commercial roofing industry, devotes significant time and resources to addressing industry-wide technical topics such as roof reflectivity.

Conducted at the Envelope Systems Research Apparatus (ESRA) at Oak Ridge National Laboratory in Oak Ridge, TN, this ground-breaking work examined changes in reflectivity on 18 different roof membranes supplied by 10 different manufacturers. The colors of these membranes ranged from whites to tans and grays.

Dr. William A. Miller, a research engineer at Oak Ridge National Laboratory, conducted the research. Miller is also the co-chair of SPRI's Accelerated Testing Task Force.

Research parameters
The ORNL/SPRI study looked at what can reduce a membrane's reflectivity and what the loss of reflectivity in roof membranes can mean, depending on what part of the U.S. they're installed in. For example, Miller notes, a decrease in reflectivity can affect total building energy costs in areas that are primarily concerned with cooling a building. By contrast, in areas where heating a building is more important, any loss in reflectivity will have little affect on building energy costs.

Furthermore, the good news is that ORNL's research discovered that reflectivity can be restored by washing the membrane surface because, Miller adds, it seems to be caused by a biomass - possibly a fungus - growing on the membrane surface that enhances the collection of dirt and other contaminants. Decreased reflectivity does not seem to be caused, he points out, by an initial breakdown in the membrane's formulation or polymer content.

Restoring reflectivity
Although reflectivity can be restored by following a manufacturer's recommended cleaning procedures, which vary from supplier to supplier, Miller warned that improper cleaning methods can void a warranty.

Whether or not washing the roof membrane is cost-effective is another question that Miller is exploring.

Miller plans to present his final report on this research to SPRI by the end of this month.

He suggests that roofing manufacturers need to develop a new, accelerated testing protocol to help forecast changes in reflectance. Likewise, he recommends that manufacturers issue specific washing procedures to maintain reflectivity.

Savvy, maintenance-oriented roofing contractors might look to investigate membrane washing as another business opportunity, after consulting with the appropriate membrane manufacturers.

Accelerated testing protocols would help manufacturers speed up the process of earning an Energy Star rating, Miller adds. This is particularly important because current Energy Star program requirements require an additional three years of field testing whenever any formulation change alters a membrane's reflectance by 5% or more.

"In this way," Miller points out, "with accelerated testing protocols, everybody could win."

Where this work goes from here is up to SPRI's Accelerated Testing Task Force.

For more information on how to enter the next SPRI competition, contact us at our new address: 411 Waverley Oaks Road, Suite 331B, Waltham, MA 02452; e-mail info@spri.org; or visit www.spri.org. Please note: SPRI's new phone number is 781-647-7026 and its new fax number is 781-647-7222.