Under a new ordinance, all new and renovated residential structures, including multifamily structures, will be required to have roofs that reflect solar rays rather than absorbing the sun’s heat. Wikimedia commons/Thomas Pintaric
In a bid to combat its urban “heat island effect,” the city of Los Angeles has passed an ordinance that requires all new or renovated residential structures to install solar reflective roofing.
January 21, 2014—Last month, the Los Angeles City Council added a new ordinance to the city’s 2014 municipal building code. Now all new and renovated residential structures—from small, single-family units to multistory apartment towers—will be required to install so-called “cool roofs,” which reflect solar rays rather than absorbing the sun’s heat and contributing to the city’s warming.
“L.A. suffers from a strong urban heat island effect of 6 ̊ F or more compared to surrounding less developed areas,” says Craig Tranby, an environmental supervisor in efficiency solutions at the Los Angeles Department of Water and Power, who wrote in response to written questions posed by Civil Engineering online.
In Los Angeles, the heat island effect has “resulted in a number of significant negative impacts on the environment, which the cool roofs will help address,” Tranby said. At the community level, these negative impacts include decreasing roof and materials life, increasing overall and peak energy consumption as consumers cool buildings with air conditioning, and increasing heat-related illness among those who cannot afford to cool their structures. More broadly, the heat island effect also increases greenhouse gas and smog formation in the atmosphere, and decreases climate resiliency within the city, according to Tranby.
Research into the need for the ordinance began when the City of Los Angeles, in partnership with the Los Angeles Regional Collaborative for Climate Action (LARC) and the U.S. Department of Energy, commissioned a regional climate study to be completed by the University of California, Los Angeles (UCLA). Conducted by the university’s department of atmospheric and oceanic sciences, the study, “Mid-Century Warming in the Los Angeles Region,” determined that with current building requirements and behavior remaining unchanged, specific locations in the city and its environs would see an annual average temperature increase of between 3.7° F and 5.4º F by sometime between 2041 and 2060, depending on each location’s development, geological formations, and nearness to the ocean.
The study also found that the number of “extreme hot days”—those days that are as hot as the seven hottest days of the year—is expected to triple by the middle of this century in coastal and central Los Angeles. The news is even worse for inland valleys, desert areas, and mountain regions. In the San Fernando Valley and San Gabriel Valley the number of extreme hot days is expected to almost quadruple. In the region’s deserts and mountains the number is expected to increase 4.5 to 6 times the current number.
Extreme heat is something with which the city is already familiar. As of the study’s publication in 2012, the hottest official day on record for downtown Los Angeles was September 27, 2010, when a temperature of 113° F was measured before the official thermometer at the University of Southern California weather station broke.
Fundamentally, “the city is going to get hotter,” says David Fink, the director of campaigns for Climate Resolve, a local nonprofit environmental group dedicated to making southern California more prosperous and livable and who helped organize the conversations that resulted in the new ordinance. “We wanted to take an approach of looking at the best solution to offset some of that warming, or even reverse it.”
Tranby agreed, noting that the UCLA study, and others, “stressed the urgency of taking local action.”
California’s Title 24 building code and industry practices that highlight the money-saving benefits of using cool roofs for commercial buildings have already resulted in cool roofs becoming more common within the city, according to Tranby. “For residential buildings, which represent a much larger area [than commercial buildings], this has not been the case and hotter asphalt roofs are dominant.” The new municipal ordinance will change that.
While cool roofs have traditionally been white, that is no longer necessarily the case, according to the Cool Roof Rating Council, an Oakland, California, trade association. The organization’s website explains that manufacturers have developed a variety of roofing products that are “highly reflective in the near infrared (non-visible) portion of the solar spectrum.” Even so, the site states, “Because a white roof strongly reflects both visible and near infrared sunlight, a white roof will typically be cooler than a cool colored roof.”
The ordinance requires the specific solar reflectance levels for the cool roofs, as measured after three years on a scale that runs from 0, which is unreflective, to 1, which is the most reflective; it also specifies the thermal emittance of the material. For roofs that are considered “low slope” and have less than 2 in. of rise over 12 in. of run, the ordinance requires a minimum three-year solar reflectance of 0.63 and a thermal emittance level of 0.75. For roofs considered “steep slope,” with more than 2 in. of rise over 12 in. of run, the ordinance requires a minimum three-year solar reflectance level of 0.20 and thermal emittance of 0.75.
Building on the UCLA study, Climate Resolve helped organize discussions among key city departments to develop the cool roof ordinance within the city. Because one of the biggest obstacles for homeowners and builders is the slightly higher upfront cost of cool roof materials, Climate Resolve approached the Los Angeles Department of Water and Power (LADWP) to see if they would be willing to expand their existing cool roof incentive to cover the additional costs of using cool roof material. Tranby represented LADWP on a joint team with the city’s department of building and safety to identify and create the incentive.
“To support the passage of the new requirement and ensure it would not pose a cost burden on residents, LADWP expanded the scope of it’s cool roof rebate to cover qualifying products under the new code,” Tranby said. “This will generally offset cost premiums. As the market makes the transition to the cooler residential products, the incentive will be adjusted accordingly.”
Cool roofs on consumer’s properties help utilities meet their energy efficiency goals, Fink says. “On a hot summer day, a cool roof can be up to 50 °F cooler than a traditional roof,” he says. By reflecting the suns rays, rather than absorbing them into the roof and building, such roofs keep the buildings cooler and reduce the need for air conditioning, he says.
Helping the city pass the cool roof ordinance is just one of the first steps in helping the city face climate change, Fink says. “Science shows that there is a certain amount of greenhouse gas already in atmosphere, and a certain level of warming will occur no mater what mitigation we do, so we need to do both [mitigation and adaptation],” he says. “We need to be preparing while we fight climate change.”