Cool roofs reflect sunlight to minimize heat absorption that contributes to higher urban temperatures, smog formation, and air conditioning costs. Furthermore, these reflective surfaces reduce greenhouse gas emissions as well as energy usage.
Environmental justice neighborhoods with few trees and households that spend more of their income on energy bills would find these resources especially useful.
Reduced Energy Consumption
Cool roofs reflect more sunlight and absorb less heat, thus decreasing a building’s energy usage and air conditioning bills. Furthermore, since cooling systems typically utilize electricity produced with fossil fuels such as coal or natural gas production plants, cutting back energy use results in reduced greenhouse gas emissions.
Cool roofing could help significantly mitigate the urban heat island effect when deployed city-wide, according to research conducted at Argonne National Laboratory. Their modeling experiment demonstrated that cool rooftops saved more cooling energy than multiple common city-scale passive and active interventions during two of summer 2018’s hottest days.
Environmental Justice communities may be particularly exposed to climate impacts and have higher utility bills. To maximize these programs’ effects, states should offer targeted funding and incentives for low-income homeowners to install cool roofs.
Reduced Greenhouse Gas Emissions
Cool roofs reduce energy consumption by reflecting rather than absorbing sunlight, providing an important tool in fighting urban heat island effect and greenhouse gas emissions. They may also lower greenhouse gas emissions by decreasing need for air conditioning or other forms of cooling devices.
Cool roofs and green roofs vary significantly in their energy-saving capabilities depending on climate conditions and location in a built environment, which should be evaluated and modeled prior to implementation. In London, we found that cool roofs and green roofs significantly decreased summer energy demand when compared with control buildings with concrete roofing; this decrease is largely attributed to cooling energy savings generated through roof-whitening; estimated carbon emission reductions amount to 11-12 kg CO2/m2 of roof area annually as a result of their installation.
Environmental justice neighborhoods benefit significantly more from tree canopy than non-environmental justice neighborhoods, since residents in those neighborhoods typically spend a greater proportion of their income on energy bills and typically have smaller tree canopies. Furthermore, when combined with other cooling infrastructure such as pavements or urban vegetation, such benefits can provide considerable climate improvements across an entire city.
Reduced Health Risks
Cool roofs reduce indoor building temperatures and air pollution levels, creating more comfortable environments and healthier environments for their inhabitants. Furthermore, cool roofs reduce outdoor temperatures to mitigate against Urban Heat Island Effect, reducing risk for illness caused by hot weather such as heat rash, stroke, exhaustion or respiratory illnesses.
Cool roofs tend to provide greater cooling benefits during summer than winter due to their ability to reflect solar radiation and lower ambient temperatures more significantly during the daytime. It should be noted that previous modeling showed that even an intensive intervention in city centres could only offset around 25% of heat-related mortality during heatwaves (Macintyre & Heaviside 2019).
States can encourage cool roofs and other strategies that mitigate the Urban Heat Island Effect through zoning ordinances, climate action plans, construction codes, standards loan programs education initiatives or voluntary initiatives. You can discover state policies that support such measures by visiting EPA’s Heat Island Community Actions Database and filtering by “Cooling Activity.” Additional resources are also available on Cool Roof Rating Council website.
Reduced Maintenance Costs
Cool roofs help buildings reduce air conditioning costs for their occupants while mitigating urban heat island effects by reflecting sunlight back onto its source, thus limiting absorption by buildings and their surroundings. This leads to lower energy usage as well as decreased emissions of greenhouse gases and air pollutants resulting in greater energy savings as well as lower greenhouse gas emissions and other forms of pollution.
At a city scale, the increased albedo of cool roofs leads to substantial citywide cooling as illustrated in Scenario 2 of our modeling experiment (See Figure D1B in Supporting Information S1). This reduction in ambient temperature reduces health risks while decreasing electricity demand during summer peaks thereby improving grid reliability and preventing outages.
Cool roofs have the greatest potential to reduce energy use in cities with hot, humid climates such as Cairo or Hong Kong where air conditioning use is high; however they can also be effective in relatively cooler cities with similar energy demands, like Seoul where their benefits may not be as dramatic. Furthermore, cool roofs can be applied across a range of buildings to increase overall system efficiency in an area.
