The Heat Island Index is on the Rise, Along with Your Energy Costs

What You Need to Know and Do About Hot Roofs

Building owners and facility managers everywhere are challenged by rising energy consumption that contributes heavily to their overall costs – and there doesn’t seem to be an end in sight.  A major part of this usage – at least half – comes from HVAC systems. Air conditioning plays a major role in driving up consumption and cost.

Unfortunately, buildings can easily become too hot. Much of a building’s heat comes directly from the sun’s rays on the roof. While some of this heat gets reflected by the roof, a good portion of it gets absorbed and transferred to the building below, significantly increasing internal temperatures and, in turn, driving up the cost to maintain a comfortable temperature for people. Black or dark roofs retain more heat, absorbing both visible and nonvisible light that can reach temperatures of 150-degree Fahrenheit or more in the summer according to the Department of Energy. In addition to making buildings hotter, hot roofs contribute to creating heat islands, which arebuilt-up urban areas that experience significantly higher temperatures than surrounding areas.

Other contributors to heat islands include closely situated buildings, which trap heat, asphalt roads and concrete sidewalks that absorb the heat from the sun as well as exhaust from buses, cars and factories.

These rising urban temperatures are measured through a heat island index, which calculates the temperature disparity between urban and rural areas. According to the Environmental Protection Agency (EPA), daytime temperatures average one to six degrees Fahrenheit hotter in urban areas vs. rural ones, and up to 22 degrees hotter at night.

The heat island index is becoming a more prevalent measurement – and soon may be as ubiquitous as the wind chill factor – because it enables us to monitor potential climate issues and put measures in place to help reduce them.

The problem with heat islands

Heat islands don’t just impact buildings and energy costs. They also have a major impact on the environment and human health. A heat island reduces air quality since the increased pollutants released into the air from exhausts from vehicles, factories and other sources don’t have an effective way to dissipate around densely packed buildings. It also worsens water quality by warming up streams and other bodies, which negatively affect aquatic life. A heat island also has a deleterious effect on humans, causing heat stroke and heat exhaustion, respiratory problems, and other health issues that can lead to illness or fatalities. As people try to escape hot temperatures, air conditioning usage increases, which in turn can cause brownouts and blackouts that exacerbate the health risks.

These environmental and health issues associated with heat islands are compounded during heat waves when temperatures soar. The health problems hit the most vulnerable populations the hardest, such as the elderly, pregnant women and children. The CDC estimated that in the period from 1979-2003 alone, 8,000 deaths were caused by excessive heat exposure, which was more than the number of fatalities from hurricanes, lightning, tornadoes, floods and earthquakes during that period combined.

Finding solutions

The good news is that there is a lot we can do to combat heat islands. Here are some of the ways cities, towns and building owners are helping to cool structures and the environment:

  • Using materials that reflect solar energy on streets, highways, parking lots and other areas to create cool pavements.
  • Planning for smart growth by creating more open spaces, promoting compact buildings, and pushing for more conservation efforts through better transportation options and other initiatives.
  • Planting trees and other vegetation to provide shade as well as reduce air and surface temperatures.
  • Planting vegetation on green roofs to reduce heat.
  • Using cool paints that reflect solar energy and reduce building temperature on cool roofs. A study conducted in California found that cool roofs can reduce annual energy costs by 50 cents per square foot.

Many of these efforts are well underway in cities and towns and can have a big impact. A study by Dr. Brian Stone, Jr. of Georgia Tech’s School of City and Regional Planning estimated that by planting more vegetation and using reflective building materials, the cities of Philadelphia, Atlanta and Phoenix could significantly prevent many of the increased fatalities expected from urban heat islands and climate change in 2050.

Best practices for building owners

Reducing heat on roofs is one of the better ways to reduce building heat.While creating green roofs is an option to reduce heat, it is more expensive and requires more maintenance than painting or coating the roof. Heat-reflecting cool paints are an effective solution for keeping roofs cool and are being required in many municipalities.  Typically, cool paints are white or light in color, because white tends to better reflect the sun’s rays.  White cool paint can come in many different forms – some are simple white acrylic paints, while others have added polymers for increased durability.

But cool paints now also come in colors other than white. Advanced polymer coating technology for cool paints available today enables black or dark colored roof coatings to reflect the sun’s infrared rays and significantly reduce heat. Regardless of the color, it’s key to look for highly durable paints that won’t crack.

With climate change, temperatures are expected to increase and exacerbate heat islands, which will continue to boost building cooling costs. With new approaches and advanced technologies, such as polymer cool paints, building owners and facility managers can significantly reduce their expenses and have a positive effect on the environment. After all, a cool roof is one of the simplest and most cost-effective building upgrades to improve energy efficiency. And a solution that saves money, is easy to use and helps environment is a win-win all the way around.


Nygra Coatings, a subsidiary of Bambu Global, provides revolutionary cool coating technology that repels heat-causing infrared radiation from roofs and other surfaces. Its coatings dramatically lower cooling and maintenance costs, and the impact of heat exposure compared to standard cool paints. Available in white, black and other colors, its robust, lightweight coatings are easily applied in just one thin layer and remain intact for 20 years. These coatings are well-suited for use on education, healthcare, commercial, industrial, military, and other facilities and assets seeking to reduce temperatures, manage cooling costs, reduce energy use and support sustainability initiatives.  For more information, visit

Share This