Cool Roofs: An Easy Upgrade


Check out Google Earth – the ‘view from above’ of your favorite American city. And look at the roofs of the office buildings, warehouses, shopping centers, and even the homes. Most of them are probably pretty dark in color – and this means they heat up a lot when the weather is warm – up to 50 degrees hotter than light roofs. All of those dark roofs mean that as a nation we’re using a lot more air conditioning than we need to. At least a billion dollars a year in extra power bills, in fact. And when you combine hot roofs with dark roads and parking lots, we get the ‘urban heat island’ effect: cities tend to be 2-5 degrees hotter than less urban areas just because of all the dark surfaces.

But there’s something we can do about it: changing to a ‘cool roof.’ The Department of Energy just did this in our Washington, DC headquarters. It was time to replace our roof anyway, so for no extra cost we went to a ‘cool’ white material. And we’re hoping others follow this lead.

A cooler roof means lower energy bills –up to 10-15% lower – when it’s warm out because your air conditioner doesn’t have to work as hard. Saving energy means lower greenhouse gas emissions because we don’t need to burn as much fossil fuel. And less heat absorbed by building rooftops means cooler communities in the summer.

Researchers at Lawrence Berkeley National Lab estimate that if just over three quarters of our nation’s commercial buildings were updated with cool roofs, the U.S. would save enough energy on air-conditioning to reduce CO2 emissions by about 6 million metric tons each year. That’s like taking more than a million cars off the road.

Places like Bermuda and the Aegean island of Santorini got this concept long ago. Nearly every rooftop is white. These folks figured out that it’s more comfortable to use a cool roof in a hot climate than to use a dark roof and blast the AC.

So if you or someone you know is planning some work on the roof of your building or home, check out whether cool roofing is a good option for your climate zone. Go to to calculate how much money you might save.

The cleanest source of energy is the energy you don’t use. We’ve realized that in the Federal government and have gotten started on making sensible changes to save the taxpayers money. We’re looking forward to businesses and householders joining us in saving money by saving energy – and then let’s all shout about it from the rooftops. Cool ones, that is.

Here’s a video of Secretary Chu giving his thoughts on our new cool roof:

Article by Cathy Zoi, Acting Under Secretary of the Department of Energy.

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  • Global Energy

    How about a cool roof with added solar panels to it? That way you can get hot water for free as well…

  • Peter Riches

    Urban planning and building control authorities worldwide should take note and facilitate this. Surface albedo has a big effect and has been used for a long time in hot countries, where they paint their houses white all over for this purpose.

    Solar panels are a good idea, too, making use of some of the energy falling on the roof. If you want a cool roof, though, I would think externally mounted panels would be preferable to integrated solar tiles, simply because they would shade that portion of the roof. This is a bit of an aside, though, because the point of a solar collector is to collect energy, not reflect it. There’s no reason these low- and high technologies cannot be used together.

  • Tom

    a cool roof can help , I believe also using a combo reflective roofing materials along with solar can go along way.