In the never ending quest for sustainability, Los Angeles is experimenting with sealing their hottest streets with a new asphalt coating created to increase solar reflectivity and, thereby, lower street temperatures.

Los Angeles, like New York City, suffers from the Urban Heat Island Effect, wherein densely populated and built environments are as much as 20 degrees hotter than outlying areas. According to the U.S. EPA, “Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.”

Can a coolant seal reverse that effect? According to the Los Angeles Daily News, Los Angeles is betting big – about $40,000 per mile – that it can. (Typical sealants run significantly less in cost.)The City recently applied its first coating of CoolSeal, which is light gray, in the hottest area in the San Fernando Valley, Canoga Park, on streets lined with two-story apartment buildings. Plans are to duplicate the experiment in 14 other council districts.

Does it work? According to the Los Angeles Daily News, using a handheld thermometer, the newly solar-reflective coated street in Canoga Park read a cool 70 degrees, as compared to a nearby black asphalt street where the temperature read 93 degrees.

CoolSeal is a product of California-based GuardTop LLC which says that the product will last seven years and “produce measurable reductions in temperatures.”

The U.S. EPA defines cool pavements as those that “reflect more solar energy, enhance water evaporation, or have been otherwise modified to remain cooler than conventional pavements.” They consider cool pavements to be important in mitigating the Urban Heat Island Effect. As there are no official standards to define cool paving materials as yet, the Transportation Research Board has formed a subcommittee to initiate an in-depth exploration.

One of the reasons research on cool pavements has lagged well behind technology for cool roofs is because pavement is considerably more complex, involving pedestrian, car and other traffic impact, landscaping, varying usages, changing shadows and thermal influences. Roofing is concerned with reflectivity only which can be achieved with a coating of products bought off the shelf.
There is much scientific testing to be done and standards to be set to advance the use of cool pavements. But, given the current interest and beginning momentum, before long, cool pavements may give new meaning to The Great (Cooler) White Way.

BTW, in answer to the long held belief that you can fry an egg on the sidewalk in very hot weather, all of the sources we checked said no. Why? Because sidewalks are lighter in color and don’t absorb as much heat as asphalt. So, can you fry an egg on asphalt? Yes. But it has to be at least 130 degrees which begs the question, “Why would you even want to try?”

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Steven_J._SchleiderBy Steven J. Schleider, MAI, LEED-AP BD + C President, Metropolitan Valuation Services