Slashdot Mirror
Bill Clinton Says 'Paint Your Roofs White'
Hugh Pickens writes "Former President Bill Clinton thinks 'every black roof in New York should be white; every roof in Chicago should be white; every roof in Little Rock should be white. Every flat tar-surface roof anywhere! In most of these places you could recover the cost of the paint and the labor in a week.' Noting that Mayor Bloomberg started a program to hire and train young people to paint New York's roofs white, Clinton says a big percentage of the kids have been able to parlay this simple work into higher-skilled training programs or energy-related retrofit jobs. The benefit: not only will 'cool roofs' lower the utility bill in every apartment house 10 to 20 percent, but it frees cash that can be spent to increase economic growth. Clinton presented this with fourteen additional ideas for growing the economy, saving energy, and attacking the jobs crisis."
I suspect they would actually make the building warmer. It's a common misconception that black absorbs heat while white reflects it. Well, that in itself isn't the misconception, the misconception is that people think of the heat transfer happening only one way. Black is more conducive to heat transfer than white. That means if you have a black roof in winter (assume no snow), and the inside of the house is warmer than the outside, the black roof will radiate the interior heat to the sky faster than would a white roof. Think of white paint as a heat insulator, and black paint as a heat conductor.
True, during daylight the radiation from sunlight into the roof may exceed the radiation from inside the house to outside. But days are short in Winter, and I suspect the heat loss during the night far exceeds the gain during the day.