In 1991, researchers coated a Merritt Island home’s green-gray shingle roof with reflective material; the shingles reached about 110°F after treatment

The temperature of shingles on top of an average suburban house can reach 160-170 degrees F on a hot July afternoon in Florida. It's not the air outside, not the attic underneath; the actual roof surface of the house becomes so hot that you'd think twice before touching it. In 1991, researchers coated the green-gray shingle roof of a home in Merritt Island, Florida, with a reflective material to observe what would happen. The surface temperature was lowered to approximately 110 degrees.

A 1995 Florida Solar Energy Center study titled “Measured Cooling Energy Savings from Reflective Roofing Systems in Florida: Field and Laboratory Research Results,” showed that the roof reflectivity of a single-story home on Merritt Island that was coated with a reflective material increased from 0.22 to 0.73, while the temperature of the shingles fell from approximately 160-170°F before treatment to about 110°F after the coating was applied. The report also found a 10.5% reduction in air-conditioning energy use at the Merritt Island test home. More than three decades later, the underlying finding remains relevant: roof reflectivity can affect how much heat a building absorbs and how much energy is needed for cooling.

Why roof color affects cooling costs


When it comes to roof color, the younger generations may not be much concerned about it. However, the physics doesn't bend: When solar rays strike a dark roof, it absorbs almost all of them, and heat has to be removed from it somewhere. Some of it spills into the attic, some of it intrudes into the living area underneath, and all of it will eventually be an issue with your air conditioning system, consequently, an issue with your monthly bill.

As per EPA records, roofs with high solar reflectance and thermal emittance can be up to 50 to 60°F cooler than conventional roofing materials during peak summer weather, directly lowering the amount of heat that is transferred into the building and lowering the strain on the AC units. It's a federal agency, not a paint company, saying this.

This isn't a sudden discovery

Since the mid-1980s, the Lawrence Berkeley National Laboratory researchers have been conducting long-term tests on the cooling effects of reflective roofs. A 2004 Berkeley Lab study on cool roofs has shown that increasing a cool roof's solar reflectance from approximately 20% (typical dark gray) to approximately 55% (weathered white) can reduce the cooling energy use by approximately 20% in a building. The lab's researchers have also calculated that a nationwide roll-out of cool roofs and cool-colored roofs would result in potential net energy savings of more than $750 million annually in the United States, according to the 2004 Berkeley Lab estimate.

Why some may still choose dark roofs anyway

If white roofs are that cool, why aren't all roofs in America white? A major reason is that residential roofs do not have to be white to achieve higher solar reflectance. Berkeley Lab researchers have developed cool-colored roofing products designed to reflect more sunlight while maintaining nonwhite colors and traditional roof aesthetics.

The truthful trade-off to be made: In cooler climates, a slightly warmer dark roof may slightly decrease the heating requirements in the winter, so it's not the same everywhere. In hot, sunny climates where air-conditioning demand is significant, reflective roofing can reduce heat gain and cooling energy use, although the size of the benefit depends on factors such as roof reflectance, insulation, duct location and air-conditioner sizing.

The takeaway

Probably you are not reroofing your apartment building this weekend, and that's ok. However, if you are a homeowner considering a reroof, a renter with any influence on building improvements, cool-colored shingles, reflective coatings and lighter roofing materials can provide alternatives to conventional dark roofing. They do not necessarily require choosing a white roof. When reroofing your home, ask about solar-reflective roofing materials and their measured solar-reflectance ratings. Roof reflectivity is one factor that can affect how much heat enters a building and how hard an air-conditioning system has to work.