Chicago, IL

Chicago Can Increase Reflected Rooftop Solar Radiation with World’s Whitest Paint Yet May Opt for Green Roofs Instead

Natalie Frank, Ph.D.

World’s whitest paint may reflect more sunlight but green roofs may be a better choice for Chicago in not only cooling buildings and decreasing climate change but also in limiting water runoff and flooding.

The climate change research community is basking in the success of Xiulin Ruan, a professor of mechanical engineering at Purdue University. Ruan has created a special paint said to be the whitest shade ever developed that could decrease the need for air conditioning and lower fossil fuel dependance. The paint is included in the 2022 edition of Guinness World Records, which became available last week.

The intention of Ruan’s team was to create a paint that would reflect sunlight and harmful solar rays away from buildings. Tests indicate that the paint reflects over 98.1 percent of dangerous solar radiation and, since it absorbs less infrared heat than it emits, any surface this paint is used on will be cooled below the temperature of the surrounding air without using any energy.

According to the research, when using this paint to cover a roof that measures about 1,000 square feet, the outcome could be a cooling power of 10 kilowatts, according to Using this new paint formulation to cover a roof area of about 1,000 square feet could result in a cooling power of 10 kilowatts. “That’s more powerful than the air conditioners used by most houses,” Ruan said.

Regular commercial grade white paint becomes warmer rather than cooler in the sun. Even paints that are created to redirect heat used on the outside of buildings only reflects 80 percent to 90 percent of sunlight without making the surface or interior any cooler.

While Chicago paints some of the roofs of buildings with reflective white paint which redirects around 90 percent of sunlight, due to other needs of the city, alternate options have been used. In particular, green roofs have been utilized instead of reflective white paint.

Green roofs are layers of living plants installed on top of buildings. They are used in Chicago on buildings as small as garages to much larger industrial structures. Green roofs have many benefits in general, some of which are particularly useful for Chicago.

In particular, these roofs help manage stormwater runoff which decreases flooding, an important function in a city that has a combined sewer system with pipes that transport both toilet flushes and street runoff. It doesn’t take more than an inch or two of rainfall to overwhelm this system which forces sewage back to where it came from. This can lead to what is known as “urban flooding,” when sewage flows into basements or even the streets. More rainfall and the city must open its floodgates letting the mix of runoff and raw sewage flow into local rivers and Lake Michigan which is Chicago’s primary source of drinking water.

Green roofs act as a sponge, decreasing the amount of runoff that occurs when it rains. They also improve the quality of the water by filtering it through the plants’ soil and root systems. This also can help cool the building, another benefit. The plants help in the winter too, providing insulation which keeps buildings warmer. The reduced energy requirements both in summer and winter have an positive effect on climate change.

Regarding, the newly develop reflective white paint, Purdue says patent applications have been filed and they are working on plans to sell it commercially by 2022. Given the needs of Chicago and the enormous amount of rooftop square footage already covered by green roofs however, this city is not likely to be one of the biggest consumers of the paint.

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