Cool roofs really can be cool

Nov 04, 2011

A recent Journal of Climate paper by Stanford’s Mark Jacobson and John Ten Hoeve (2011) on urban heat islands and cool roofs is a useful contribution to the literature. However, their results regarding white roofs are preliminary and uncertain. Along with our own work at the Lawrence Berkeley National Lab, other published papers have addressed the broader benefits of white roofs. In our view, these studies taken together raise important issues that need to be considered from a policy standpoint to fully understand the potential of more reflective (white or cool) surfaces.

Jacobson and Ten Hoeve note that reflecting light from white roofs may lead to a decrease in cloud cover, thereby increasing, not decreasing, the urban heat effect. But they also note that their findings might change if they used different models. This is an ongoing research area not only for their group, but others, and ours as well. The findings should not be considered settled.

We have found that do provide a low-cost solution that can help buildings reduce energy costs, in a wide variety of climates, as well as cool the atmosphere regionally and globally. We have also found disadvantages. The reflective roofs may cause unwanted glare, for example, and may modestly increase heating costs in winter. But answers to these issues are exactly the ones we’re working hard to find.

Our work has shown that reflective roofs can lead to better air quality, reduce the strain on our electrical grid, improve comfort and decrease emissions from power plants. These are important considerations when evaluating all the available research.

In our opinion, all of these arguments and studies suggest that selective use of white and other reflective roofs makes sense as part of an integrated strategy for more sustainable human existence on Earth. But the potential benefits offered by do not diminish the need for sustained reductions in greenhouse gas emissions to control global climate, or the need for increased use of renewable energy sources.

It’s important for the public to understand that scientific debate leads to better science. But it’s also important that the public receives—and the news media delivers—a message that properly conveys research news with all its many caveats and cautions. It’s not settled, until it’s settled.

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1 / 5 (3) Nov 04, 2011
One of the stupider things science is wasting time on. It is a fact that darker roofs help keep a house warmer during the winter. Trying to heat a house in winter 100% of the time, uses a lot of fuel which causes more air pollution and wasteful energy use. In the summer time you can open the windows and doors if necessary but you do not have to use energy except maybe to cool the bedroom.
1 / 5 (1) Nov 05, 2011
How stupid is assuming that everyone lives in a temperate climate where it gets cold in winter and never hot enough in the summer to make opening doors and windows unbearable? How stupid is it to forget that during the winter the sun is at a lower elevation and thus does not illuminate roofs with as much duration or intensity as during the summer? How stupid would it be to ignore the possibility that a white roof would allow an insulating cap of snow to linger longer during the winter? Science isn't wasting its time on this subject, and you haven't spent nearly enough time thinking about it.
1 / 5 (1) Nov 05, 2011
"It is a fact that darker roofs help keep a house warmer during the winter." - Alarson

Nope, sorry you are entirely wrong if your house is properly insulated.

A properly insulated home has a foot thick layer of insulation above the ceiling and the attic is open to the outside environment to remove water vapour and prevent condensation.

The temperature of the roof is essentially irrelevant to a properly constructed house.

"Trying to heat a house in winter 100% of the time, uses a lot of fuel." - Alarson

One home I took part in constructing had 6 inch thick, well insulated walls and low emissivity, high efficiency windows. Heating even during the coldest days of winter was done primarily by sunlight.

Shoddy construction produces buildings that are expensive to heat and cool.

Even half way rational construction methods will produce a home that requires very little heating or cooling at all.

1 / 5 (1) Nov 05, 2011
"How stupid would it be to ignore the possibility that a white roof would allow an insulating cap of snow to linger longer during the winter?" - Barakn

It is very true that my white roof has a coating of several inches of snow for several days after a light snowstorm while the darker roofs around me are clear within a lesser period of time.

However since my attic is very well insulated, snow cap or no, it matters not one bit to me in terms of heating.

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