Green Wombat often highlights high tech when it comes to tackling global warming and energy independence. But a new study from the University of California’s Lawrence Berkeley National Laboratory shows that simply installing white roofs on homes and commercial buildings – to reflect the sun’s rays rather than absorb them – can reduce air-conditioning costs by 20% and could save $1 billion a year in energy outlays in the United States.
Switch to cool sidewalks and roads and the savings rise to $2 billion annually, according to the study by scientists Hashem Akbari and Surabi Menon and California Energy Commissioner Art Rosenfeld to be published in the journal Climate Change.
The scientists calculated that a global white roofs and roads effort would offset 44 billion metric tons of greenhouse gas emissions, or more than a year’s worth of carbon, and help stablize future C02 emission increases.
“The 44 Gt CO2-equivalent offset potential for cool roofs and cool pavements would counteract
the effect of the growth in CO2-equivalent emission rates for 11 years,” according to the authors.
Such emission reductions, of course, can be securitized into tradable carbon credits, which the study estimates would be worth $1.1 trillion. Regulated carbon market exist in places like Europe but securities based on cool roofs have not yet been created.
A global cool roofs agreement could avoid the pitfalls of Kyoto-style accords, the scientists note. “Installing cool roofs and cool pavements in cities worldwide does not need delicate negotiations between nations in terms of curbing each country’s CO2 emission rates.”
It’s one of those low-tech, commonsense solutions to both energy use and global warming – one used for thousands of years in the regions like the Mediterranean; those picturesque villages overlooking the sea are white-washed for a reason.
In California, commercial buildings with flat roofs have been required to cool it since 2005. But one of the biggest hurdles in the U.S. to doing the white thing may be homeowner associations that dictate everything from the color of your mailbox to where you place your rubbish bin. The vast majority of homes in California either have standard black shingle roofs or Spanish-style red tiles. A proposal to paint those roofs white will likely incite architectural outrage.
But there’s another, albeit much more expensive solution, to hot roofs: Cover them with solar panels.
Green Wombat 
How about painting with high gloss metallic gold or silver? The reflectivity of those are way much better than white paint, and they would look “golden” or “silvery” rich.
I agree that the best to use are solar panels, only if they become very cheap.
While going to a manufactured white colored roofs and “white” pavements may _help_, the better solution would be to get back to GREEN cover.
Stones/cement convert solar energy into heat and will absorb and hold that heat, creating heat islands. This is a fact of life. Bull-dozing everything in site and paving it creates artificial heat-sinks (heat islands).
Plants convert the sunlight into plant material, oxygen, and nutrients instead of into heat.
If you want to make “green” roofs, then make GREEN roofs. If you want to reduce heat build up in the cities(reducing emissions from electic plants by reducing the need for air conditioning), then plant parks, put planters on side-walks, encourage soddies/turf roofs or even better, roof gardens.
“Green” live roofs could be more expensive and they require water, and water do not come cheap in some areas. Gray water could be used in those cases. Green cover may need some enhanced structural support, but that depends on the design of the roof garden and what type of plants are grown.
Paints are way cheaper, and using highly reflective or light colored hues would certainly help by reflecting the light back into space. Large snow covered areas have been lost forever, and those should be supplemented, and painting white on roofs is a good start.
You would have to consider the glare that white or metallic roofs would have. Perhaps one doesn’t think of this in flat areas where every building is at the same elevation, but many places are hilly, mountainous, or have taller buildings amidsts shorter buildings.
I’m looking out the window now and imagining all the currently dark-colored roofs as white. Some of the buildings are already white so I have an immediate visual comparison. Yikes, this hurts my eyes and it’s not even that sunny right now.
On another note, I used to live in a house with double-paned windows which provides a tremendous amount of extra insulation, which means both keeping the heat out when it’s hot outside and keeping the heat in when it’s cold outside. Now I live in a house with single-pane windows and the difference is very noticeable. It is a simple physics concept of transfer of heat energy through convection versus conduction.
Another University study years ago researched the benefits of adding attic insulation. Among other things that they found: They made a record of what color roofs the houses were and found that white roofs saved about 22% in the summer time for air conditioning savings, but cost 4% in the winter time for extra heating. So white roofs result in a good amount of energy savings.
And if you add ceramic to the paint or get the ceramic already mixed at the factory the cooling effect is even higher.
The reason you see a parapit wall on roofs in most Mediterranean and tropical countries is to ward off that glare caused by white painted roofs! Just look around and you will find solutions! This idea is nothing new. Just noticed by the western scientists.
If we built a big umbrella to shade the earth we could save money in the summer as well. But what about my tan??
This is another useless study that trys to justify its point by including everyone doing it. Even if it was a good idea, it is very unlikely that more than 5% would waste the time doing it. And would it cost just as much to repaint roofs and residewalk and repave roads and maintain.
And if you coat the roof and exterior walls of the buildings with photocatalyst from a company called Green Come True, then we never have to use petroleum based cleaning products ever to keep them clean. This will significantly contribute to the global warming crisis.
I live in the northeast. What about all the energy I save in the winter because I have a dark roof?
There are currently no manufacturers that create white asphalt shingles. Will someone please fill this need?
Where is the common sense? How much energy will be needed for 100 million homes to paint their roofs white. Someone has to make the paint, transport it, and a crew to come out and paint your roof? Won’t this extra carbon emmission offset any savings from a cool roof?
Now that everyone has a cooler house, how are we supposed to cool the atmosphere now that its been heated up with all these white roofs? No reduction in carbon emmissions will offset all this extra heat going into our atmosphere.
There is no question that white roofs are effective at reducing energy costs, particularly in cooling climates. While this approach to using reflective surfaces to save energy and reduce the heat island effect is sound, it is encountering significant resistance from the aesthetic perspective in the steep slope residential community.
Fortunately, there has been a considerable amount of research done by both the Florida Solar Energy Center and the Oak Ridge National Laboratory to show that ventilated roof systems such as concrete and clay tile are just as effective at reducing heat gain into the structure and maintain their effectiveness indefinitely whereas white roofs invariably lose their effectiveness as they age and become soiled.
In much the same manner that dual-glazed windows reduce heat loss, these ventilated systems offer a more practical alternative that still allows the building designer some freedom in color selection although light-colored roofs will still improve the performance and help reduce the heat island effect.
Most of the roofs use tar based shingles. I have not heard of white tar. I am sure they can find an easier way to make cooler roofs. But till then planting more trees will have a better effect.
I agree with the writter HOA’s have a lot of say in this aspect and are not going to change easily. This why I choose not to live in one.
About 6 months ago I painted my shingled roof with a white roofing paint and the results are amazing. It used to be that after 8:30am I could not go into the attic because of the heat, but now I could literally sit in there and have a picnic at 2:00pm. I have no doubt that I’m saving big on my cooling costs.
In response to Billy from Charlotte, NC, since the roofs are white they will reflect back the suns ray in the form of short wave radiation which does not contribute to global warming. It is the absorbed heat that is radiated as long wave radiation that excites CO2 and other gases in the atmosphere which causes global warming. These roofs simply mimic snow caps and glaciers which reflect the suns light, the loss of which is causing a self feeding cycle in global warming.
in response to billy, white roofing products are already and have been available for a long time. They are just not popular especially for homes. White rubber membrane roofing for flat top roofs can be bought now. White rubberized paint can be applied to black roof as well. White Composite shingles are available at Home Depot and Lowes and any other Hardware store. If they don’t carry it you just have to ask. It’s easier to find in the south. So basically it won’t cost any more energy than is currently used. Consumers just need to make the choice to use the white materials. I don’t know why this is big news to anyone. White reflects light and keeps things cool. Black absorbs heat and makes things hot. I think I learned that in elementary school.
Wouldn’t this make you use more energy in the winter to heat your home? There are always trade offs.
Larry: “Wouldn’t this make you use more energy in the winter to heat your home?”
Heat loss through the roof is generally insignificant. It’s the windows that get you.
Owens corning makes a composite shingle in Shasta White which I have on my outbuilding and Aspen Gray, which is white and gray shades, which I have on my house.
i has not a idea but with making that in summer white and in winter with dark solar cell would even be more energy saving and too energy and to gicve a state support about that too would be good
f.
Many houses in Portugal especially in the south along the coast already have white roofs – most probably for a few hundred years. Pavements are also made from white cobbled stones (with black patterns). I believe Greece also has white roofs. I think it is time the US catches up to the rest of the world. Portugal already had the largest solar power plant, tidal power and one of the fastest growing wind farms (they own Horizon in the US). The US definitely needs to invest more in alternative fuels…not waste money in wars in oil rich countries.
Have any of these “brilliant” scientists who said we should have white roofs and ASPHALT been on a white roof on a sunny day? You can barely see with sunglasses ON. Where’s the environmental advantage in having car wrecks littering the highways because no one can see?
I see a red door and I want it painted black No colors anymore I want them to turn black …
Carbon credits are a joke. White roof or green (as in plant) in the south. Either black or green (as in plant) for the north. Plant covers are most ideal with many benefits known and more not recognized by MOST. HOA rules should be overridden for the sake of the enviroment. Don’t you people ever get it? You slow ss sheep need a swift kick in the ss. Again.
What about the additional heating costs in the winter????
Dan in Indiana: I don’t see the correlation between a white roof and a car wreck. No one advocated that we paint asphalt white. What’s the sense in that? Why not just switch to concrete roads? Besides the benefit in reflecting heat, the durability is greater than asphalt. Get out of your flying car and come back down to earth.
“Where’s the environmental advantage in having car wrecks littering the highways because no one can see?
”
Dan apparently your not one of the brilliant scientists. Do you go blind when you see white cars? Probably not… actually chrome/silver reflects more (hence mirrors). White is the absence of color… and just doesn’t absorb the kind of heat other colors do… but its not the strongest reflector either.
what about some inches of soil and grass on the roof to keep the heat out in summer and inside in wintertimes?
What is needed is a push, prod or shove, to the building industry to adapt ‘earth friendly’ building practices.
Perhaps a Government sponsored green building organization could consult with all builders on new practices to incorporate.
The planet can’t wait for the builders and paying public to adapt on their own. ANd with the downturn in the housing industry, what better time to implement.
TVW in Columbus: Apparently you didn’t read the above article. They mention “The scientists calculated that a global white roofs and roads”. One can infer from what they said that they mean they want white roads (whiter than concrete?). I’m just responding to the story as written.
Patrick in Cincinnati: Your right. I’m not a scientist. I’m an engineer. It surely, though, sounds like you’re neither. To answer your question, no I don’t go blind when I see white cars. The fact that they are a multi-surfaced object helps to diffuse the sunlight. Obviously, you’ve never been on a white membrane roof in California or Florida. I have. The surface is FLAT. Do you know what that means? The surface reflects light very well. Ever walk outside into a field of fresh snow on a sunny day. I bet you squinted at the very least.
“White is the absence of color”??? Again showing you are not a scientist nor engineer. White is actually comprised of every wavelength of light in the visible spectrum. Black is the absence of color. Out of all the actual colors, by definition (since white is all colors combined) white is the best reflector (mirrors, of course, aren’t colors, they just reflect light with near 100% efficiency.
Anyway, Patrick, I was just indicating that if we painted our roads white, like the scientists in the story advocate, the roads would be awfully bright on the days designed to reflect heat. Pay attention.
Seems to be Dan is pretty sharp… there are apparently some folks who forgot 7th grade science class ’round here.
Switch to cool sidewalks and roads and the savings rise to $2 billion annually – Right out of the story… seems like someone is advocating it by tossing in a large, but unmeasured, dollar amount to it.
Dan in Cincinatti–Patrick is right. White is the absense of color in pigments. You combine blue, red and yellow paint and you get black. In light white is all the colors combined.
Many commercial property roofs are already close to being white, and have been so for 50 years or more. They frequently use lightly-colored gravel over tar, or asphalt shingles with embedded gravel. Thet defunitely are not black. Check out some google earth views of your nearby metro area.
The best thing is to deploy solar panels on the rooftops of 1-2 story buildings (where the rooftop absorbs most heat), and use low-e windows (mirror-like) on tall buildings (where the rooftop area is a small fraction of the building’s total surface area)
They would have to come up with a solution other than painting the roads. When you get paint wet it gets really slick.
Looks like White is the new Black.
Daniel in Bethlehem – I live in Indianapolis, not Cincinnati.
Patrick (and yourself) may be right if he(you) is(are) talking about pigments. However, I was talking about perception, light waves. I don’t see pigments, I see light waves. Therefore, when I look at a white road, I see all wavelengths of light reflected off of the road surface (less the ones that are scattered due to surface texture, of course). Technically, in pigments, if you combined red, blue and yellow (or any other three opposite colors on the color wheel) you would get grey not black. The only way to get black with pigments is to use black pigments.
The point of a white roof reflecting heat is to reduce the energy you need to cool the interior space. Right??? How does switching road colors to a reflective white save us on energy expeditures? What interior space is defined by a road?????? I understand the advantage of a white roof but I don’t understand what white roads accomplishes. Anyone have any insight on this?
Better yet, cover those roads, sidewalks and roofs with trees and plants; you can convert heat to biomass, cooling and sequestering carbon.
Adam from Jacksonville – my guess is that they are wanting to try to reduce the effect of ‘thermal islands’ or ‘urban heat islands’ by reducing the surface area that absorbs sunlight/heat and radiates back at night raising the need for air conditioning.
Wow, would have thought? When its sunny out and 90 degrees must people would go with a white t-shrit over a black. Pretty basic concept.
Can I paint my roof gold? I like “bling.”
Great idea!!!!!!!!!!!!!!
How about using a small solar panel to run a pump that would spray water(rainwater from a cistern) on a roof so that evaporation would cool it?
Seem like it would help
I wonder how sod roofs compare to white roofs for energy efficiency? One thing to consider: sod (or any plant material for that matter) is capable of carbon capture, not just preventing more carbon expenditure. Maybe the weight is not practical for the large flat surface of commercial buildings.
But how much extra would it cost for heating in the winter? And the potential extra costs for white coverings.
It’d cost me more, since I don’t pay for air conditioning.
Rick- The thing about black bodies and white bodies is that whereas black bodies are capable of absorbing energy (in this case visible light) more than white bodies, that means that they will also radiate it more. What this means is that a black roof will also radiate your home’s internal heat more than a white roof. I believe this is referred to as a black-body radiator.
If you put foam insulation on the roof sheathing inside the attic, not batt insulation on the ceilings, it also reduces the heat inside the house. I did this in south florida. I could go into my attic at 1PM during the day, middle of summer, and the temperature was only about 10-12 degrees warmer than inside the house.
What ever you think you are saving in your energy bill is more than compensated by the amount paid on the new roof. This is not Wombat, it’s Dingbat.
White roof = good, even in North East. Cuts the summer heat gain.
How to off-set winter heat-gain? Follow EPA Guidelines for R-49 in attic, then follow it up with a Radiant Barrier.
Just adding the Radiant Barrier to my 10″ insulation reduced my Oil Consumption by 17%. (now at 750 Gal/Year for 2300 Square-foot Colonial, 4-person family) Imagine what it would have done if I had the full R-49!
I’ve since done more work this Summer to mitigate heat loss in the winter, and I expect to cut my Oil Consumption by another 10%. All without burning any alternative fuels like Pellet Stoves.
I also added two mini-split heat-pump systems, which I hope reduces my consumtion furthur. They already cut my Summer cooling electric consumption by 14.5% over Window units.
Note, I use Consumption numbers, not costs. It is the consumption that matters!!!
Al from Baltimore – Maybe you should consider something else besides yourself and how something benefits you. This is a solution to climate change-related disasters. Tell the families losing their homes to Katrina, Ike, Gustav, and all the millions of people feeling the impacts of climate change in less-developed countries that you don’t see the benefit in painting your roof white because it wouldn’t provide an immediate cost reduction in your electric bill.
How would all of this reflection affect the earth’s albedo (currently at around 30% maybe?)? What kind of affects would this have on our climate I wonder?
Oh boy… Obviously the people posting here (and the writer) know little about emissivity (just enough to be dangerous). That’s not a “low tech” way to cool it down, that’s a “no tech” way to do it wrong.
While true, a white painted roof will reflect more VISIBLE light waves, it does not necessarily mean that it will make it reflect much more heat…
While it’s true that VISIBLE light is made up of all of the VISIBLE colors of the light spectrum, that has little or NOTHING to do with the thermal radiation spectrum (Heat, AKA infrared AKA IR).
Emissivity (E) can be defined as the percentage of absorption and emittance of a given spectrum of light waves. Simply put, a substance that is high E will absorb and emit more IR. A substance that is low E will reflect and retain more IR.
The scientific value range is from 0 to 1, both extremes being only theoretical. So you typically see values expressed as “0.2”, which means that it will absorb/emit 20% of all thermal radiation at a given spectrum, (the rest, 80%, is reflected or retained). So for a roof, the lower the value, the better. Most tar/asphalt/spanish tile roofs are in the 0.85 to 0.096 emissivity range.
If this makes your brain hurt, stop reading now, as it gets way more complex than that.
The emissivity of a given object (paint, tile, whatever) usually changes quite radically with temperature, unless it has an fairly wide band-gap (more on that later). This means that hotter objects tend to absorb/emit more IR (heat) than cooler objects of the same material that are being subjected to the same thermal radiation (IR). Simply put, the hotter the object gets, the faster it absorbs and emits heat.
The actual VISIBLE color has only a little to do (some but not much) with how a substance either absorbs or reflects IR (infrared). It has much more to do with how the substance interacts at the atomic level with IR. Yes, black things do tend to absorb/emit more heat, but only because it also absorbs IR better than most other “visible” colors. And that has to do with what makes a pigment or object black (hint: usually carbon or an oxide, which is typically high E).
A given “generic white paint” might have an IR emissivity only a little lower (10% at best) than say an asphalt roof, unless it was specifically formulated (think nano tech) to have a lower emissivity. And their are such paints, but only for interior walls so far. So don’t go out and slap any white paint on it, it probably won’t work as well as you might think.
What materials do work you ask? Well the guy that mentioned gold (Au) was spot on (although gold “paint” wouldn’t work). PURE gold metal reflects almost all IR, and has a extremely wide band-gap (which means its emissivity goes up very little with ambient temperature). It’s emissivity is rated around 0.02 (2%) or less.
Obviously, a gold plated roof is way too expensive. So, what’s almost as good, but much cheaper? Try aluminum. Aluminum’s (Al) emissivity is only 0.04 (4%), and it’s cheap.
Now, don’t run out and get any old “aluminum paint”, as that too won’t work (there are some brands designed for this, but most aren’t). Paint has binders and other chemicals in them, which BTW are usually based on hydrocarbons (remember, carbon is high E?). And the FAA might have something to say to you if you put polished aluminum panels on a roof, possibly blinding any pilots in overhead aircraft. Even if you could, it would quickly get dirty (smog, dirt, bird poop), and absorb more heat (constant maintenance keeping it clean).
The place to put it is underneath the roof, in between the rafters where there is an air space (you need at least a 3/4″ air gap, or it don’t work). It will tend to stay much cleaner there (no bird poop), and this also doubles the effectiveness of the AL, because now both sides of it are reflecting/retaining heat energy (Hint: what’s 4% of 4%?).
Aluminum radiant barriers are usually sold in rolls of cellular plastic foam with aluminum foil adhered to both sides of it. You staple it to the edges of the rafter studs.
As far as what to put on the actual surface of the roof to help out? I’d say either thermal solar collectors (not PV), or the cheapest and most effective anti-carbon footprint would be plants surrounded by grass (no bare dirt, it’s high E). Obviously, plants only work on a flat roof.
Why plants? Not only do they naturally keep your roof cooler, cost almost nothing, and collect CO2… If you grow eatable crops and eat them, you also don’t contribute to the fuel used to bring food to your local store (think tomatoes or strawberry’s from Mexico & South America). Not to mention that trip to the store in your car. Sounds like something a hippie might do, don’t it?
For a standard residential (not flat) roof, go with the radiant barrier in the rafters as your best choice. Although the surface temperature of the outer roof will not change, it will make a dramatic impact on the attic temperatures (assuming you have proper roof ventilation), and will actually multiply the effectiveness of any standard insulation you already have up there, because less heat differential makes most standard insulation more efficient.
After 12 noon I have tall trees that spread overhead and shade 85% of my 2800 square foot roof area(2000 sq ft living area), last month of august when the temperatures average 93 everyday my electric bill stays quite low compared to friends with the same size house without trees shading them. by keeping the A/C at 78 during the day and 75 at night I’m at half the electric bill that others in the constant sun have. so if possible have your house shaded by trees.
Pat L in Browerville – Wow! You are right on. This is one of the most intelligent comments I have ever seen. It is unbelievable (and sad) that most people don’t really understand the underlying physics that control their everyday lives (and utility bills!).