Generally, at least in the spring and summer months, urban and metropolitan developments are hotter than surrounding rural areas due to crowding, the use of more engines, and the high concentration of metal conductors amongst a myriad of other reasons. They call these areas “heat islands,” and in most cases, architects and city planners have accounted for it—installing high albedo or "cool" roofs as well as reflective pavements to effectively bounce the heat away (The International Green Construction Code mandates heat island mitigation for not less than 50 percent of site hardscape, including that the hardscape materials be light colored with a Solar Reflectance Index of at least 29).However, new research from Arizona State University has challenged what we thought we knew about making a city heat-proof—especially in the non-roof hardscape (or pavement) department.
The report by Jiachuan Yang, Zhihua Wang, Ph.D., and Kamil E. Kaloush, Ph.D., P.E., of the ASU National Center of Excellence for SMART Innovations suggests that the current design of most pavements out there simply relies too much on reflectivity to decrease the heat island effect. In addition, it overlooks the intricacies of urban geography and how ground level reflections interact with pedestrians, vehicles, and the surrounding environment.And, as we live through some of the hottest years in modern history due to global warming and climate change, it’s vital that our cities are equipped to remain livable from mild May to sweltering August.
According to a recent article on Environmental News Network, “Specific areas of concern identified include increased cooling loads (and energy costs) for buildings subjected to solar reflections, increased light pollution from illumination at nighttime, increased wintertime snow and ice buildup even with additional deicing salts, and even human health concerns from UV radiation to visual glare.”
"Unfortunately, efforts to promote reflective pavements have moved more quickly than the scientific and engineering research. As this report indicates, reflective pavements may cool a pavement’s surface but there can also be negative environmental and social impacts on the areas adjacent to the pavement," said Heather Dylla, Ph.D., Director of Sustainable Engineering for the National Asphalt Association.
ASU has since passed its research torch on to the Asphat Pavement Alliance, which made waves at this year’s Greenbuild International Conference and Expo in Philadelphia.