Using Cool Roofs to Reduce Urban Heat Islands

cool roof installed on a house

During the day, buildings, streets, and sidewalks absorb heat. This thermal emittance increases the surrounding air temperature and contributes to climate change. Reflective roof surfaces, known as cool roofs, cause a cooling effect by reflecting heat rather than absorbing it.

An eco-friendly investment, cool roofs help with heat island mitigation. Discover more about the urban island heat effect and how this type of roofing system can reduce the heat produced in urban environments.

What is a Cool Roof?

graphic showing how a cool roof works
Photo Credit: Juan Rodriguez

The defining feature of a cool roof is its reflective surface. Normally, roofs absorb heat from the sun, which increases the surface temperature of the roof. But a cool roof reflects sunlight instead of absorbing it.

The Cool Roof Rating Council (CRRC) classifies these roofs as having high thermal emittance and solar reflectance, also known as albedo. Albedo measures how reflective a surface is and how much heat it absorbs from the sun.

Even sloped or flat roofs found on residential, industrial, or commercial buildings can be turned into cool roofs. As long as they have a light-colored surface and high solar reflectance, many types of roofing materials can be cool roofs. Some examples include:

Aside from installing a cool roofing material, homeowners can simply paint their roofs a lighter color. They also can use a special reflective coating, such as:

  • Acrylic
  • Aluminum
  • Asphalt shingle granules
  • Latex
  • Paint
  • Polyurethane
  • SEBS
  • Silicone
  • Urethane

Conventional roofs store a lot of heat, sometimes reaching temperatures over 150 degrees Fahrenheit. So, if you want a cooler home and environment, it’s important to switch to a cool roof.

What is the Urban Heat Island Effect?

Urban heat islands (UHIs) occur when temperatures in urban areas become hotter than the neighboring rural areas because of the amount of heat absorbed by artificial substances such as metal, asphalt, concrete, and glass. When the sun shines on these materials, they absorb heat – increasing the air temperature around them.

This effect is most pronounced in city areas with a lot of infrastructure where artificial materials have replaced natural vegetation. The temperature difference created by urban heat islands can be significant, sometimes increasing city temperature by as much as 10 degrees Fahrenheit.

Urban heat islands are problematic for many reasons:

  • Blisteringly hot and uncomfortable living conditions
  • Increased risk of heat-related deaths, like heat stroke
  • Higher energy consumption and energy costs
  • Harmful impact on the environment
  • Decrease in work productivity

According to the United States Environmental Protection Agency, heat islands increase urban temperatures by around 1 to 7 degrees Fahrenheit during the day.

Interestingly, the effects of an urban heat island are most noticeable at night because all the heat absorbed by artificial materials during the day is released during the night. At night, this thermal emittance increases the city’s air temperature by 2 to 5 degrees Fahrenheit.

After sundown, people expect the air to cool down their living area for a soothing respite. Without this cool-down phase of the day, there can be severe health repercussions.

How Do Cool Roofs Reverse the Urban Heat Island Effect?

Summer days in the city are unbearably hot, with bright sunshine glaring off concrete walkways and metal siding. All the artificial materials in a city absorb heat, which in turn increases the area’s temperature.

The urban heat island effect is harmful and widespread, as it affects the climate of an entire city, which in turn has a negative impact on the health, economics, and comfort of the homeowners.

While merely switching to a cool roof may not seem like a big contribution in the scheme of things, every little bit helps. And the first step towards a cooler city climate starts with you – and your roof.

Cool roofs are an important contribution to reversing the effect of urban heat islands, as they have:

  • High reflectivity
  • Less heat absorption
  • Low thermal emittance
  • Reduced heat conduction
  • Lower ambient air temperature

Having a cool roof not only helps cool down the outside climate but also keeps indoor temperatures cooler as well. You’ll also reduce your carbon footprint, as these roofs are significantly cooler and more eco-friendly than conventional roofs.

Benefits of a Cool Roof

a building's cool roof made of glass
Photo Credit: LancerE / Flickr / License

Apart from helping mitigate urban heat islands, owning a cool roof has many benefits:

  • Maintains stable indoor temperatures: One of the biggest benefits of cool roofs is that they decrease indoor temperatures by 2.2 to 5.9 degrees Fahrenheit, thereby reducing energy costs and creating a more comfortable living area.
  • Saves money on energy bills: By keeping your home cooler, cool roofs reduce energy consumption, so you won’t have to spend as much on energy bills.
  • Protects air conditioner units from deterioration: Cooler temperatures put less strain on air conditioning units, so they won’t break down as quickly. It also reduces installation and HVAC repair costs.
  • Decreases air pollution: High temperatures increase greenhouse gas emissions and create more smog in the city. Merely switching to a cool roof helps improve city air quality by decreasing energy usage.
  • Extends roof’s life expectancy: In hot weather conditions, your roof absorbs more heat, shortening its lifespan. Cool roofs last longer by reflecting sunlight instead of absorbing it.
  • Increases energy savings: By assisting in cooling the climate, cool roofs reduce energy consumption, making them a greener option.
  • Decrease in health problems: More heat in the city may lead to more smog, which is bad for health and may cause respiratory health problems.
  • Reduces strain on the electrical grid: When the entire city temperature rises, so does the amount of energy required to condition the air in city buildings. If this happens, electrical grids can become overloaded and may even cause a blackout.
  • Rebates: Depending on your location, the Environmental Protection Agency and the Department of Energy may be offering rebates for homes with cool roofs. In some areas, it is actually a building requirement for homes to have a cool roof installed.

When to Get a Cool Roof

Whether you’re looking for the best roofing material for your new home or your old roof needs a replacement, it’s a good idea to consider getting a cool roof if you:

  • Live in a region with a hot climate
  • Plan to reduce your carbon footprint
  • Want to save money by reducing the strain on your HVAC unit and keeping your house cooler – especially during the summer months

Cost and local climate are some factors you should consider while deciding if a cool roof is right for you. Your budget always comes into consideration whenever you are planning a big home improvement project. Luckily, a cool roof doesn’t necessarily cost more than a normal roof.

If cost is the issue, an alternative solution is to have your roof painted a lighter color to make it a cool roof. But your current roofing material should be compatible with getting a new paint job. Merely changing your roof’s color to light-colored paint improves your roof’s energy efficiency by reducing the amount of heat it absorbs.

The downside of cool roofs is that your HVAC unit might have to work harder to heat your home in the winter since, during the freezing winter months, the heat absorbed from the sun can be beneficial in helping keep your home warmer.

FAQ About Cool Roofs

Are There Other Ways To Reduce an Urban Heat Island?

Yes, there are other ways to help lessen the negative impact of heat on urban environments. Apart from installing a cool roof, you can do the following mitigation strategies to help reduce urban heat islands:

– Open windows to generate natural airflow and cool your home
– Use white or other light-colored paint for your pavement
– Add more plants and water features to your garden
– Use energy-efficient appliances
– Plant more shade trees
– Start a rooftop garden
– Install a green roof
– Install solar panels

What is the Difference Between a Green Roof and a Cool Roof?

A cool roof uses a reflective roof surface to reflect heat instead of absorbing it. On the other hand, a green roof relies on shade provided by plants and the process of evapotranspiration – a mixture of evaporation and transpiration.

While their methods are different, both are eco-friendly roofing options that help reduce urban heat islands.

What Color is Best for a Cool Roof?

You might assume that a cool roof must be white. Indeed, white roofs are the best type of cool roofs since they reflect 60% to 90% of the sun. The rule of thumb is that the lighter the color, the more energy-efficient it will be.

But thanks to technological developments, cool roofs now come in a wide variety of energy-efficient colors, even dark colors, which reflect about 30% to 60% of sunlight.

Help Reduce Heat With a Cool Roof

Taking care of our planet is crucial for our resources to last – not just for us but for the generations to come. Even something as simple as changing your roof’s color from dark to light can have a big impact on the environment.

Ready to help lower local temperatures and save money on air conditioning? Find a local roofing company near you to get a new cool roof installed. Cool roofs absorb less heat, keeping your living area, and ultimately your city, cooler.

Main Image Credit: Idaho National Laboratory / Flickr / CC BY 2.0

Danielle Gorski

Danielle Gorski lives with her family in Texas. She has a degree in Professional Studies and a minor in marketing. Her hobbies include reading, drawing, and writing.