What Is a Cool Roof? Cool Roof Systems Explained

"A cool roof is designed to reflect more sunlight than a conventional roof, absorbing less solar energy," explains the U.S. Department of Energy. In turn, this roof helps lower the temperature of the building. The concept is similar to wearing light-colored clothing in hot weather. Your clothing reflects the sunlight and helps keep you cool. A cool roof reflects sunlight and helps keep the roof and overall building cooler.

Many types of roofing materials offer "cool" roof options depending on the product color and formulation. 

"The surface solar reflectance of the roofing product—the outermost layer of the roof exposed to the sun—determines whether the roof is cool or not," says the U.S. Department of Energy.   

For low slope roofs, these products include specific: 

• High SRI rated single-ply membrane
• High SRI rated modified bitumen membranes
• Reflective coatings
• Metal roofs using light colors
• Green (vegetative) roof coverings (while vegetative roofs aren't reflective, they are still heat-mitigating)

A roof has to meet particular criteria to be designated "cool." The requirements vary depending on the classifying organization and local government, so check with a qualified contractor or design professional before making assumptions about a roof's official rating. 

While cool roof coatings or materials can be retrofitted onto a building during a repair or replacement, the easiest and most affordable way to get a cool roof is by planning for it in the construction phase. Cool roofs can cost about the same as non-cool alternatives. 

Not sure if a cool roof is suitable for your climate or building? Try the Roof Explorer. Answer three questions and get roof recommendations that consider your location, reflectivity regulations, hail risk, and building type/use.  

Cool roofs benefit building owners, occupants, and the community surrounding them. 

If you operate or own a building with a cool roof, you can expect: 

• Reduced air conditioning needs, and thus lower energy bills. Energy Star® estimates a cool roof can reduce cooling demand by 10–15%, and the California Energy Commission reports that cool roofs can provide an average yearly net savings of close to 50 cents per square foot. Energy bills are further supported by the fact that cool roofs help reduce thermal heat gain/thermal emission into the space directly beneath the roofing layer. 
• More efficiency out of smaller or older air conditioning units. 
• Longer roof service life. Cool roofs reflect harmful ultraviolet and infrared radiation that damages many roofs over time. 
• Potential tax rebates. Check for local rebate and grant programs in your area, and research  the IRS Section 179 deduction. Section 179 allows you to deduct certain improvements (like roofing) to existing non-residential buildings.

If you live or work in a building with a cool roof, you can expect: 

• A more comfortable indoor environment, especially if your space isn't air-conditioned. 
• Improved health and safety, as cool roofs reduce temperatures inside buildings helping prevent heat-related illnesses and deaths, notes the Environmental Protection Agency (EPA). 

If you live in a community near a building with a cool roof, you can expect: 

• Reduced air pollution and greenhouse gas emissions, according to the EPA.  
• Reduced “urban heat island” effects. "Urban temperatures can be 2°–10°F higher than nearby rural areas" because dark surfaces, like many roofs, absorb heat. A cool roof, however, reflects more heat, and lowers the ambient temperature by reducing the amount of heat transferred from the roof to the air. 
• Improved air quality. According to the Berkeley Lab, "Cool roofs decrease urban air temperatures and thus slow the formation of ground level ozone," which is the main ingredient in smog. 
• Less strain on the electrical grid and decreased risk for power outages. The Berkeley Lab adds that less use of air conditioning helps mitigate peak energy demand during heat waves and hot summer days.