AT&T painted two Nevada telecom roofs white; roof surfaces cooled 35–40°F, reached 12°F below outdoor air, and two buildings saved about 0.5 kWh of electricity a day

Somewhere across the vast stretches of the Nevada desert are hundreds of small concrete boxes, each about the size of a garden shed. Sitting about 12 miles apart, these buildings ensure that AT&T’s fiber-optic communications remain powerful as they travel across the country. During summer 2000, the engineers wanted to find out whether something as simple as paint color could help them reduce energy costs. According to the study from Lawrence Berkeley National Laboratory's Heat Island Group, researchers tracked three of these "regen" buildings through a Nevada summer and watched what happened before and after their roofs were painted white.

Why a roof's colour matters more than you'd think

Dark roofs absorb sunlight and turn it into heat, which finds its way into the building, causing air conditioning systems to work extra hard. Light roofs, however, reflect most of the energy from the sun back into outer space. This process is referred to as “albedo,” the amount of light reflected by a surface instead of being absorbed.


Three buildings, one real-world test

The researchers chose three locations: Washoe, which is located 20 miles to the south of Reno; Battle Mountain, 200 miles to the east of Reno; and Carlin, 60 miles to the east of Battle Mountain. Each building was a small concrete structure with a surface area of 160 sq. ft. and an initial gray-green roof. According to the findings of the study, the initial reflectance of all three roofs was about 26%. Then in late July 2000, the roofs were coated with a white ceramic coating that increased their reflectance to about 72%. Sensors on the roof surface, under the roof, in the attic and inside the building recorded temperatures every 15 seconds for months, before and after the paint job.

The roofs cooled down dramatically

The findings were quite notable. Before the paint was applied, roof surfaces were 25° to 35°F hotter than the surrounding air temperature. The study notes that after the paint, roof surface temperatures dropped about 35° to 40°F lower than before. At their coolest point during the day, roof surfaces reached up to 12°F below the surrounding outdoor air temperature, a peak measurement, not the typical swing, made possible by how effectively a bright white surface sheds heat back into a clear desert sky. The change was also seen in the attic: before the coating, the air was hotter than the outdoor air all day, but afterward it was 15 to 18°F cooler during the day and only slightly warmer at night.

The electricity savings were modest but still count

For the first two buildings, Battle Mountain and Carlin, the white roofs helped in saving about 0.5 kWh of electricity each day, which amounts to $12.50 annually based on the rate of electricity consumption in the study. For the third building, Washoe, there were savings of almost 13 kWh a day, but the study found that the difference came from the efficiency of its two air conditioners, not the white roof.

By itself, half a kilowatt-hour a day is nothing out of the ordinary. The study projects annual savings of about 125 kWh per building, based on roughly 250 sunny days of air-conditioning use per year, rather than a full 365, which works out to an accumulated 3,750 kWh over a roof's 30-year lifespan. The study also highlights an important distinction: coating these particular roofs after construction, out in remote parts of Nevada, costs real money in labor and materials. Since the prefabricated roofs already come painted at the factory, specifying white instead of gray-green from the start would add no extra cost at all, meaning the payback period for that choice, specifically, is effectively zero. This observation is part of a wider range of scientific studies about reflective roofs. In a 1997 study, ‘Peak power and cooling energy savings of high-albedo roofs,’ published in the journal Energy and Buildings, Akbari and colleagues showed that the effect can be much stronger in other contexts: cooling energy dropped by about 35 percent for two schools in Sacramento and around 80 percent for one Sacramento house when reflective paint was applied. The regen buildings in Nevada may have used little energy to begin with, since they housed equipment rather than people, which helps explain why the percentage savings were small even though the roof cooling was substantial.

The bigger picture for cities

Cool roofs aren't just a magic fix for lonely desert buildings. The US Environmental Protection Agency's guidance on cool roofs explains how reflective roofing often helps cities fight against the "urban heat island" effect, where dense buildings and dark surfaces trap heat and increase local temperatures. The agency also states that cooler roofs can help reduce stress on electrical systems during heatwaves. The Nevada experiment probably won't win awards for the size of its savings and that's almost the point. Sustainability doesn't always have to involve money or be something extravagant to make an impact; sometimes they just need to be free, easy, and applied at scale. The next time a building gets a fresh coat of paint, the colour on top might be doing more work than anyone expects.