Cool Roofs Protect the Environment and Save Money

Energy Secretary Dr. Steven Chu recently made headlines by calling for the widespread use of "cool roofs" as a smart way to combat climate change.

The idea was oversimplified in the news media as simply "painting the world white," but that is not what Secretary Chu suggested. In fact, it is a caricature of what could be an important way to offset our carbon emissions. Secretary Chu is correct in suggesting we pursue cool roofs, and I hope more people will learn about this new strategy and consider adopting it for their homes and businesses.

If nothing else, a white or cool roof will save you up to 20 percent on your air conditioning bill and it's hard to argue with that. Over its lifecycle, a new white roof costs no more than a traditional roof.

The basic idea behind cool roofs is simple and recognized for centuries by the ancient Greeks and Egyptians. Dark colors absorb more heat than light colors. It's for this reason that people living in the tropics wear light-colored clothes and the same reason you don't lean on a black car on a hot day. Similarly, darker colored roofs retain more of the heat from sunlight within our atmosphere. But light roofs reflect more of that light straight back into space. Therefore, making roofs lighter in color increases their solar reflectivity and directly offsets CO2 emissions.

The potential savings are both huge and surprising. My colleagues and I have estimated that replacing urban roofs with solar-reflective materials in tropical and temperate regions of the world would offset 24 billion tons of CO2.

Let me explain. The average US roof is approximately 1,000 square feet and lasts for about 20 years. A white roof produces a one-time offset of 10 tons of CO2 and would eliminate emissions from one car for more than 2.5 years. Considered on a national scale, the equivalent would be eliminating two billion tons of CO2 emissions or removing 20 million cars off the road for 20 years. From a global perspective, replacing dark roofs with cool ones would be equivalent to taking half the world's cars - 300 million vehicles -- off the road for 20 years or reducing 24 billion tons of CO2 emissions for the same period.

That may sound too good to be true, but it is possible.

Because most large, modern cities have dark roofs, roads, and parking lots, they tend to run 5-10% hotter and create the "urban heat island" effect. Cool roofs mitigate the "urban heat island" effect and improve outdoor air quality and comfort. Light-colored roofs have other benefits. Most importantly, they lower temperatures inside of homes and businesses, thereby reducing the need for air-conditioning during the hot summer months. That translates to additional savings in CO2 emissions.

Since 2005, California building standards have required that any flat roof on a new building be a white roof. The California will soon also require new residential roofs to have cool colors as a way to reduce cooling costs. In an effort to cut its power costs, the city of Phoenix recently invested $28,600 of its $4.3 million in housing funding from the American Recovery and Reinvestment Act to apply reflective white paint on the roof of a public housing complex.

Simply put, a cool roof will save money for homeowners and businesses through reduced air conditioning costs. The real question is not whether we should move toward cool roof technology: it's why we haven't done it sooner.

Kudos to Dr. Chu for examining the science and embracing this sensible approach in combating climate change.

Dr. Art Rosenfeld is a member of the California Energy Commission.

Comments

[oakley9]

what about winter time?

[MsEngineer]

It is all about the greedy, me first mentality and lack of awareness that prevails in our culture. I was flipping through the TV channels a while back and came across a golf tournament set in the Southwest, Arizona I think. Here was Tiger Woods and other really rich golfers playing on a golf course set in the middle of a freaking desert. Did it occur to anybody playing there that there is something wrong with lush green fairways in the middle of rocks and sand? Did Tiger ever scratch his head and say maybe I should be playing somewhere that doesn't need to irrigate every inch of grass? Did it even occur to these rich guys that something wasn't right about this? We are giving up a lot of water so rich people can play golf in the desert and get richer while doing it.

And then there is auto racing. A several thousand people drive their cars and RV's to the track to watch a bunch of guys race cars. How much fuel is this wasting in one day?

[GeeBee]

Golfers sometimes jokingly refer to their game as "a good walk spoiled". I prefer to think of it in many cases as a waste of land, though some Scottish courses do actually graze sheep (and the Scottish climate removes the need for irrigation).

As for auto racing, the audience's fuel consumption is no worse than any other sporting event, but much of the technology developed for auto racing finds its way into street cars. Electronic engine management alone has saved a lot of fuel and cleaned the air in places like Los Angeles.

[MsEngineer]

This is a fairly entertaining thread!! White roofs are great. And blacktop parking lots should be outlawed. However, the problems we face are far more complex.

First, although he seems a little whacky, sonofsamphm1c has a point about deforestation which is a major issue in third world countries that needs to be resolved.

Second, we need to stop the population explosions in third world countries that have led to over farming and droughts in much of Africa and Asia.

Next, we need to stop over fishing. Once, it was thought there was a unending supply of food in the ocean but now we know that is not true.

Also, we need to stop being so greedy. HGTV just had a show on where the homeowners had two wells plus were requesting a commercial water meter on their house because a standard residential water meter wasn't big enough. Does one family really need or have the right to that much water??

This will be a long drawn out fight between the people who don't want to give up what they have today and the people who recognize that future generations have a right to water and clean air.

[Jeff Roth]

I HAVE SPRAY PAINTED MY ROOF WITH A WHITE/BEIGE COLOR. IT IS SIMPLE AND IT SEEMS TO BE HARMLESS. THE ROOFING COMPANIES WILL TELL YOU NO. BUT I KNOW SOMEONE WHO DID IT 2O YEARS AGO, AND THEIR ASPAHLT SHINGLE ROOF STILL HOLDS UP. Yes, cans of spraypaint are toxic, wasteful, and do have their own carbon footprint. However, clearly the lifetime impact of a white roof over a black-ish one is obvious! SUFFICE IT TO SAY, THE STRUCTURE STAYS 4-5 DEGREES COOLER INSIDE IN DIRECT SUN THAN IT HAD BEFORE.

ALSO, i was thinking about this today myself, WHAT IF THERE WERE A LAW MANDATING THAT ALL BLACK-TOP PARKING LOTS BE PAINTED WHITE?! Yes they'd get "dirtier" over time, but they'd never be as dark as they are now. Haven't you ever seen the heat waves roiling off a blacktop parking lot? I saw it today and thought about this. As Bill Clinton would say, this is the "Low Hanging Fruit" of energy efficiency and climate change mitigation. THIS OUGHT TO BE DONE NOW. It's simple, easy, cheap, and effective.!!! PLUS IT COULD CREATE A TON OF JOBS IN CREATING AND APPYING THE MATERIALS.

Seriously ought to be considered.

[KillTheMessenger]

Now... how about... we mount solar panels on top of parking lots? I can show you millions of square feet that soak cars in the sun. Just the ones I in my neighborhood could generate 5MW of peak power in summer.

[tomasedison]

Cool idea.

[yomimi]

yes, cool roofs will help. but while everybody debates and twiddles their thumbs, do something simple today. memo to couch potatoes: change your tv settings to use less energy. you won't even notice the difference, except in your electric bill, which will be lower. you'll also offset your methane emissions from farting on your couch on nfl sundays.

[KillTheMessenger]

Now you are talking about something really effective. Good idea!

[GeeBee]

How exactly does one alter settings on a TV to save energy (other than hitting "off")?

[KillTheMessenger]

You turn down the brightness on a plasma. And newer LCDs allow to dim the background lights rather than reduce the light transmission through the actual display. Sometimes they call that "energy savings" or "green" modes. If you need more time from the batteries of your notebook, the single most effective measure is to reduce LCD brightness.

[MamandesFilles]

Why is it still difficult to get information through to the public? That's easy. As a person who helped write Chicago Energy Code which has roof reflectivity requirements & an individual who rehabbed her house adding green elements I can tell you that building professionals need to be convinced that green changes are cost efficient and aesthetically pleasing. And cost of operation should be considered when building.

You needn't have a snow white roof to green your roof. I have a standing seam metal roof on my house that is champagne. The undercoating of the roofing material helps reflect solar energy off the roof. Because it is metal, the roof cools down very quickly after the sun sets. My air conditioning costs have dropped dramatically. I had to fight my builder for that roof. He thought I was crazy to pay more for a roof to save on the operations side. I had that same fight about my bamboo floors which take 5 years v. 20 to be grown & my on demand hot water heater.

Chicago has been a leader when it comes to the greening of the urban environment. Our City Hall rooftop garden is a model of retrofitting existing structures. Our Center For Green Technology was the first LEED Platinum building in the State of Illinois. Working in cooperation with ComEd, solar panels were installed on area museums & schools. I was proud to be part of those programs & continue to advocate for greener options.

[RexOzone]

The obvious sometimes requires motivation to become apparent. Solar arrays upon each roof will be reflective (like ice) and power everything we need. And new fluffy insulation cooled my house and warmed it by 15 degrees. Don't tell the energy companies...let's just do it. Revenge motivates too.

[sej100]

All structures should have solar panels. We need an investment in the manufacturing and distribution of solar panels. Right now installing a new solar paneled roof requires a large outlay of cash. More than most people with a mortgage can comfortably afford right now.

[sonofsamphm1c]

I am a big advocate of this. It would do great deal to reverse the urban heat island.

I noticed a recent National Geographic article about "green" roofs - lots of plants and a waterproof membrane. These roofs are anything but green. A green roof is one that replaces the lost white that is melting away in the Arctic Ocean. Plants on a roof are nothing but misplaced vanity.

Somebody needs to consider paying 3rd-world farmers to maintain their depleted land in white sheeting. It would be far smarter than allowing them to move on to cutting down forest and plowing up virgin soil. Creating a surface area of white roughly the size of Australia - all structure roofs, all transportation vehicles, all sidewalks and little-used roadways, and managed white surfaces on depleted land - would replace lost white from melting, and adding white beyond the lost area due to melting would reverse warming.

[KillTheMessenger]

So you want to do terraforming on Terra? For what? So you don't have to give up coal fired power plants, which are the actual source of the problem? Are you aware that a solar farm the size of Australia would generate humanity's energy needs dozens of times over? So why cover a continent in white foil when all you have to do is to cover your roof in solar panels to be done with the problem?

I don't get it. Does anybody here?

[sonofsamphm1c]

All fossil fuels are the problem, not just coal.

Much of the heat is already in the pipeline. Building enough solar panels to cover humanity's needs is fine. It is a gigantic project to will release a huge amount of CO2, which just puts more heat into the pipeline.

At some point mankind will have to engineer cooling.

[WilliePilgrim]

The math and engineering on this solution for making our roofs and paved surfaces white have been done and are very impressive. It's also very easy, which my increasingly suspicous mind has lately been thinking is one of the reasons it's being ridiculed by the "league of cap and trade advocates".
Even if global warming weren't a concern, this kind of approach would still be good for our quality of life and even save us money in the long run...just as looking at our lowlying coastal areas with an eye towards flooding would be a great idea even if sea-level rising wasn't a concern...we still will have floods due to tsunamis, bollide impacts and tectonic subsidence.
It is the reluctance of those who espouse green solutions but have only the understanding of the issue one would get from watching TV news or popular magazines that cause me greatest concern. Instead of simple solutions they are eager and adamant about a complex financial scheme that by virtue of its size will engender the greatest amount of corruption due to greed that has ever been experiences, created by the same mindset that gave us the derivates market...can we not pull our heads out of our collective fundaments to acknowledge Al Gore is nice and smart guy but his solutions are the stuff that have brought us to the brink.

[KillTheMessenger]

Actually, it is you who is getting suckered into a one time feelgood solution. Even if we did this on 100% of all roofs on earth, the net effect would only stop global warming for ten years. After that it would continue as if nothing had happened.

The real answer is to replace coal fired power plants with solar panels... on the very same roofs that would be painted white. The solar panel will insulate your roof just as well as the white paint will, it can reflect infrared radiation back to space if required and it will save many tons of CO2 emissions over its lifetime... which the white roof will not.

The choice is not cap and trade or white roof as you want us to believe. The choice is coal fired power plants or solar energy. That is the only choice we have, unless you want some 4000 new nuclear power plants on earth, of course. That would work, too.

[23000Days]

White roof: $3 S/F, Solar panels: $150.00 S/F.

[Thermodynamics]

This needs to be a law in the sunny states. Why a law?

If you want a white roof and your wife prefers a textured brown roof, guess what happens?

We do need to green up our building codes.

[Indra]

For the most part a good idea. However in my case it would not work as I live in a cold snowy region and a dark roof helps ice melt and heats the home in the winter. We get very few hot summer days where I live.

[libwingoflibwing]

For people living in regions like yours white roofs are not a good idea. For people living in the southwest they are.

But what about people with cold winters and hot summers? We need to go beyond white roofs or brown roofs to smart roofs that are white on sunny hot days and brown on cold days.

[MamandesFilles]

You are more likely to cause ice dams in your roofing materials having a dark roof. Research at Lawerence Berkley National Labs shows that dark roofs do virtually nothing to keep a home warm in the winter.

[KillTheMessenger]

A dark roof wont, but a solar collector will heat a home. Again... why stop at passive methods to conserve energy when we have perfectly well developed active ones? Zero energy homes are basically stock items now that plenty of architects can design for you from stock components. All we need to do is to make it law that new homes have to conserve more energy and old ones have to be retrofitted.

[Jeff Roth]

That's non-sensical. The color of the roof is not going to influence the melting of snow generally if the roof is covered in snow. Right?

[Mugzi]

You know, Christie Brinkley suggested this same idea quite a few years ago. When it came time to re-roof my home I chose reflective metal, maybe it's my imagination, but my electric bill has gone down when others have gone up.

[wadenelson1]

Has anyone actually done the math & physics on this?

Won't any reflected light simply bounce up and down in the atmosphere, increasing the air temps and offsetting any air conditioning savings?

It's not going to get radiated back out into space, i know that much.

You may save on your INDIVIDUAL air conditioning bill but if everyone was to do it I suspect it would be self-defeating

[AuntSally]

Actually, reflected visible light does leave the Earth system. That is, it does indeed radiate back into space. Our atmosphere is transparent (for the most part) to visible light, which is why it's able to reach us from the sun in the first place. Consequently, it travels back out just as easily as it traveled in.

Now, the real question is about infrared. While most of the sun's energy is carried in the visible part of the spectrum, there is still substantial energy in the IR. What you also want in a roof, then, is one that is not only reflective in the visible, but in the IR as well...

[KillTheMessenger]

Where the white roof idea breaks down is that while it does prevent the shift from short wavelengths that can escape the greenhouse effect to long wavelengths that can not, it's a one time feelgood measure. It does not save significant amounts of CO2 when compared to installing solar panels on these roofs, therefor all the heat it deflects comes back a decade later as additional blanketing by the added CO2 emissions from our coal fired power plants that we did not replace with solar energy.

Now, I am sure that the makers of white paint love the idea since it would put tens of billions into their pockets. But as an environmental measure it's kind of a dud.

[KillTheMessenger]

Actually, people have done the math and physics on this. It's a very active field. What you "know" is wrong. Short wavelengths (above a um or so) do not scatter much in the atmosphere ("scattering" is the correct term for "bouncing") Since most of the energy in sunlight is contained in these short wavelengths, the light just passes through. However, once the radiation is absorbed on the ground, the peak of the radiation temperature shifts from 5600K, the temperature of the sun to 300+K, the temperature of the earth. The wavelength is thus shifted down by a factor of 15 or so, landing you in the 5-10um range. And it happens that triatomic molecules with a significant electric dipole moment (like H2O and CO2) happen to have strong molecular resonances at those frequencies (in the 10^14Hz range). Therefor these molecules scatter the long wavelength IR radiated back from the heated ground strongly and form a blanket around the earth. Without this effect the planet would be nothing but a lifeless ball of ice. However, with too much CO2 it will become much hotter and it won't support the kind of mammalian life that is adapted to a cool planet any longer. That's the wet greenhouse which gave the dinosaurs and their precursors such a good time.

[WilliePilgrim]

I guess that's why Mars with an atmosphere of 95% CO2 is so swealtering.
I jest, of course. CO2 can only moderate temps so much and then its ability to interfer with IR is saturated. An atmosphere with an extra few hundred PPMs wont cause that much more interference anymore than putting an extra hat ontop of your head when it's cold out will cause your body to warm much.
Also...the arguement that runaway warming will eliminate mammalian life overestimates CO2's capacity to interfer with radiation and underestimates the negative feedback loops as described in Lovelock's "gaia" scenario, as well as mammalian tenacity for survival.

[MamandesFilles]

Yes, check Lawrence Berkley National Labs. They can even tell you which colors are more reflective. Some are obvious. Others are not.

http://heatisland.lbl.gov/CoolRoofs/

Also NASA has done alot of work showing the connection between dark surfaces (roofs, roads, parking lots, etc. and the Urban Heat Island Effect.

http://www.nasa.gov/centers/goddard/news/topstory/2004/0801uhigreen.html

[KillTheMessenger]

Urban heat island effects are not global warming. The best way to deal with heat island effects is to have better city planning. A modern city should be planned with mixed high density development with plenty of parks and green areas. Sadly, real estate developers do not earn money on parks... so most cities are incredibly poorly laid out for the sake of profiteers.