Want to save some dough on summer cooling costs? Paint your roof white. Seriously.
Assuming your local homeowner’s association won’t go spastic (and they might), you can save a decent amount in summer cooling costs if you simply paint your roof white. It sounds kind of odd, but it really works — and people in other countries have been doing it for centuries.
Most people know that light bounces off the color white without being absorbed. There’s a good reason for this: anything we perceive as white actually reflects all wavelengths of light equally, and it’s that mixture we perceive. As Newton proved way back when, white is what you get when you mix all the other colors together.
Well, all the colors of light, anyway. When you mix all the colors of paint together, you get kind of a muddy grayish-brown. But I digress.
Anyhoo: if solar radiation isn’t absorbed, it doesn’t turn into heat. That’s why buildings in hot climates tend to be a pale color, top to bottom: it’s an easy way to stay cooler.
So Why Don’t We Do It?
Some people in sunnier areas of the continent, like the Southwest, actually did adopt light-colored walls and roofs early on, but most parts of the country didn’t. It’s hard to say why, but it’s probably due to a combination of historical continuity and available materials.
That is, most European countries didn’t use the heat reducing reflection trick because they didn’t need to, so we just kept up the tradition; and most regions of the country didn’t have the necessary materials (e.g. pale stone, adobe, and stucco) readily available.
Basically, we don’t do it today because we have air conditioning.
Is It Worth the Effort?
You bet! Assuming your nosy neighbors and the authorities will allow it (you should check on both), painting your roof white can save 10-15% per 1,000 square feet of roof on your annual cooling costs.
Since you can easily rack up hundreds of dollars in cooling costs during the warmer months, those are substantial savings. Painting the roof can pay for itself in a year or two, especially if you do it yourself and use cheap or recycled paint. It doesn’t have to be fancy.
From an ecological perspective, you can decrease your carbon footprint significantly with a white roof. The same study that yielded the 10-15% savings figure found that a white roof decreases carbon dioxide output by 10 metric tons per 1,000 square feet, because your AC doesn’t have to work as hard.
Many houses have roofs that are bigger than 1,000 square feet, which means you can probably nab even better benefits than I’ve outlined above if you do decide to paint your roof white — so good luck!