Cool Surfaces: Roofs and Roads
Los Angeles is the first U.S. city to set a citywide temperature reduction goal, and switching to cool surfaces is a key strategy for achieving that goal. Los Angeles’s goal is to reduce the urban heat island effect by 1.7°F by 2025 and average temperature 3°F by 2035, but the city is 40 percent covered by pavement. Los Angeles’s reflective paving program, which targets both rooftops and public streets, complements other UHI reduction programs including a Million Trees initiative and integrated planning with the Department of Health.
“The lived experience of Los Angeles is that the place is getting hotter,” explains Greg Spotts, assistant director of the Los Angeles Bureau of Street Services (StreetsLA). “When we got started, I thought that the main potential of cool surfaces was reduced indoor temperatures, reduced air conditioning use, and reduced carbon emissions.”
An epidemiologist showed us the trends in heat-related illnesses and deaths and how those trends are supposed to go through the roof as cities get hotter. That created a very powerful drive. — Greg Spotts, Assistant Director, Los Angeles Bureau of Street Services
Extreme Heat Resilience Strategies
The Los Angeles Green Building Code’s cool roof requirement was implemented in 2014 for residential buildings. Managed by the city’s Department of Buildings and Safety, residential buildings must meet minimum values for 30-year aged solar reflectance and thermal emittance, a combination of two numbers measuring both how much light energy a material bounces back, or solar reflectance, and how well a material rejects heat, or thermal emittance.
The original SRI standard at the county level about doubled the reflectance of a traditional asphalt shingle and set different rates for flat and steep roofs. In 2018, the city of Los Angeles independently increased the SRI requirements to 0.25 for steep slope and 0.8 for flat roofs.
In addition, the Los Angeles Department of Water and Power (LADWP), a city-owned utility, offers cool roof rebates between $0.20 and $0.30 per square foot to eligible single- and multifamily residential customers.
Partnering with a California-based manufacturer of a gray, highly reflective coating, StreetsLA began a three-part test to confirm that the reflective topcoat would adhere to road safety standards. Following rigorous testing in the StreetsLA Materials Testing Lab and a pilot on a parking lot, StreetsLA secured $150,000 in funding in early 2017 to coat one residential city block in each of the 15 city districts.
Outcome
The cool roof requirements have resulted in a minimum of 20,000 new cool roofs in Los Angeles. “The feedback we’re getting is universally positive,” says Jonathan Parfrey, executive director of Climate Resolve, a nonprofit organization that helped define the new benchmarks. “No one is saying they have to pay more for a cool roof because the properties are getting an immediate payback and paying less on utility bills.” Los Angeles’s building code has also changed the materials market regionally; manufacturers have virtually stopped supplying roofing materials that do not meet the city’s SRI standards.
The properties are getting an immediate payback and paying
less on utility bills. –Jonathan Parfrey, Executive Director, Climate Resolve
At the street level, the cool paving has decreased surface temperatures by about 10°F although the tests have revealed other challenges. Half the city block pilot projects, for example, were recoated by the topcoat manufacturer with a slightly altered reflective formula in 2018 to address observed sealant flaking and decreased reflectance in some of the test sites. The StreetsLA Materials Testing Lab continues to visit each site once a month to take temperature measurements.
StreetsLA has enjoyed significant press and social media attention around the world. The first installation of cool paint on a city block coincided with the hottest weekend of that year to date; StreetsLA did five impromptu interviews with local TV stations that day. Since then, the pavement testing has been featured in the national and international press as well as in a short ATTN video that drew over 20 million views on Facebook (compared to StreetsLA’s typical 5,000 to 10,000 views).
The next two phases of testing began in early summer 2019. In May, StreetsLA began testing cool streets at neighborhood level, coating about nine adjacent city blocks in three different residential areas.
StreetsLA is also planning to evaluate reflective paving as one solution in a community-driven one-mile cooling initiative around a bus rapid transit station in California’s San Fernando Valley. The initiative is funded by a $354,000 Adaptation Planning Grant from the California Department of Transportation and a minimum in-kind $46,000 match from the city. The transit station serves a population that may be at risk from extreme heat; the neighborhood is a local “hot spot,” and residents are predominantly cost-burdened renters, highly dependent on public transit and active transportation, Hispanic, and have a median income of about 60 percent of California’s median household income. The results of this “last mile” cooling project will inform Los Angeles’s planned future work to update the climate adaptation and land use components of 35 community plans.
