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White is the new green in roofs

In 2009, Al Gore and Mayor Michael Bloomberg pushed for the painting of one million square feet of roofs in New York City and launched "NYC Cool Roofs." The plan was to reduce energy costs and give college students a job.  It at least got people thinking about the color of their roof.

A white roof performs better in two areas over the typical dark colored roof. It reduces the surface temperature and cools the surroundings.

A white surface reflects sunlight before it can be absorbed and transformed into heat energy. In the process the surface temperature is reduced by as much as 30 degrees. The lower surface temperature reduces air conditioning and saves anywhere from 5-40% in electrical savings.

Seems the big factor is how much insulation is on the roof. The thicker the insulation the less impact surface temperature makes on the interior temperatures of the building. So if you have hardly any insulation on your roof you could paint it white and save some cash but if you have 5-6 inches of insulation you probably won’t notice a difference.

The other attribute of a white roof is it reduces the amount of heat re-radiated back to the surroundings. The phenomenon known as the heat island effect is best seen in cities like Phoenix where is does not cool down during the evening like the surrounding countryside.  So much heat energy has been absorbed by all the dark surfaces that it continues to heat the air even after the sun goes down. Some areas of the country can experience 10 degrees difference but probably not in Iowa.

I don’t think the time will come when the Iowa roofscape looks like those cities from Indiana Jones movies with the minarets and desert in the background. The cities with all white roofs are most likely never white from snow. But I wonder how long it will be before white roofs are a permanent part of landscape in Iowa. 

- Rob Smith


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