On a sunny afternoon, the typically dark, impermeable surfaces of urban roofs and pavements can get warm in the sun and in turn heat the air. The air temperature in nearby rural areas tends to be cooler, because those surfaces are more reflective and permeable.
Higher urban air temperatures compared to rural air temperatures is called the urban heat island effect. Urban heat islands (“UHIs”) can increase energy use, degrade air quality and aggravate heat-related illnesses in cities. In addition, there is concern about UHIs contributing to global warming.
Over the past decade, metropolitan areas have worked to address the UHI effect – on a national and global scale. As the second-largest urban region in the U.S., and with the highest heat island effect in California1, Los Angeles has demonstrated strong commitment and leadership with these efforts. LA’s “cool community” strategies include cool roofs, pavements, walls and urban vegetation measures. In 2015, LA became the first major city to mandate cool roofs for new residential construction projects in response to the heat island effect.
Los Angeles Cool Roof Ordinance
The first of its kind, the Los Angeles Cool Roof Ordinance2 is intended to help the city:
- become more resilient and healthier on hot days
- reduce heat-related hospitalizations
- improve air quality by reducing the formation of ozone
- inoculate against power outages
- reduce homeowners’ electricity bills
- reduce greenhouse gas emissions
- provide a more pleasant home environment
By helping to keep temperatures down, cool roofs can help protect lives, lower bills by increasing energy efficiency, and help combat global climate change at the local level.3
Cool roofs reflect more sunlight and absorb less heat than a standard roof, thereby saving energy and money by using less air conditioning. Installing a cool roof instead of a warm roof can benefit buildings, cities, and the planet by reducing:
- conduction of heat into the building
- convection of heat into the outside air
- thermal radiation of heat into the atmosphere4
Carrie Niezgocki is the Marketing Supervisor in the Industrial Mineral Products Division of 3M.
1 Totten, Sanden. “LA area has highest urban heat island effect in California” 21 Sept. 2015. Southern California Public Radio. Web. 14 July 2016.
2 “LA: First Major City to Mandate Cool Roofs on All New Residences.” Climate Resolve. 17 December 2013.
3 Phillips, Ari. “Los Angeles Becomes First Major City to Require ‘Cool Roofs.’” Climate Progress. 18 Dec. 2013. Think Progress. Web. 14 July 2016.
4 “Cool Science, Cool Roofs.” Heat Island Group. Lawrence Berkeley National Laboratory. Web.