Painting roofs white can actually help lower the temperature of a city

The idea of painting roads and rooftops white in order to combat carbon emissions has been around for years. It is surprisingly simple and effective and yet has not been implemented much.

A study at the Lawrence Berkeley National Laboratory found that cooler pavement and roofs leads to cooler cities and an overall cooler world.

Since buildings with white roofs reflect far more sun than those with black roofs, these buildings stay cooler. Less air conditioning has to be used, lowering the overall energy required to run the building.

Also buildings with black roofs heat the space below them and this heat is carried spread by the wind. This raises the ambient air temperature in what is known as the urban heat island effect. Black roofs also radiate energy back into the atmosphere to be absorbed by clouds. This heat is then trapped by the greenhouse effect.

As such, white roofs is one of the quickest and most cost-effective ways to reduce our carbon emissions. In an initiative launched by the Energy Department, the federal government hopes to exemplify the benefits by using these light roofs on their buildings.

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Reply to
Metspitzer
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I say it's total BS. The best study I saw on roof color was done in FL. They took a bunch of identical houses, put varying types and color of roofs on them, fully instrumented the houses, and measured during AC season.

The conclusion was that if you had a shingle roof, it made about a 10% difference in energy usage if you had a black rood or a white roof. And that was the energy usage with the houses unoccupied. They did another test when they were occupied and the energy usage difference dropped to just a few percent. Which makes sense, because when occupied the energy usage is going to be higher, because people are opening door, turning on TVs, cooking, etc.

It would also seem to me that it's junk science to suggest that lighter roofs lead to a cooler world. X amount of solar radiation is hitting the earth. Almost all of it is going to go into heating it. So, it's hard to believe that because something is white that radiation is going back from earth to outer space.

Reply to
trader4

Here's an aerial view of Disney's Epcot Center. Notice the white roofs. Disney knows what the f*ck they are doing!

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Reply to
Mitt Romley

The limiting factor here would be carbon emissions. The idea of white roofs making the house cooler is half a century old or more.

Thanks.

I didn't want a white roof because I was afraid it would look worse when it got dirty, so my next door n'bor and I replaced our roofs with light brown. I can tell the difference. Even when the roof fan is turned off, it no longer gets so hot on the second floor that I can't go there. It's always moderately comfortable on the second floor (and less hot than that on the main floor and cool in the basement) (I only use AC about 10 days a summer, and last summer not at all because it was broken.)

OTOH, I used to use the attic heat to heat the house the last part of fall and first part of spring, and the attic doesn't get hot enough to do that anymore.

In Indianapolis, I used to drive by the home of one of the richest guys in town, and the new home of his son. Brown asphalt shingles. By the end of the firs summer, the brown shingles were off and white shingles were on. This was about 1962. The benefits of a white roof have been known for a long time.

And check out your car. Why people buy black cars, with black seats no less, anywhere but the Yukon, escapes me. It takes more AC to cool them, and unless you use a remote starter, it's like Hell from the time you get in the car until the AC has finally cooled it off some. I have a light tan roof, white seats, and a tan steering wheel. I can get in the car, sit on the seat with short pants on, and touch the wheel without suffering on the hottest summer day, whether the convertible top is up or down.

Reply to
micky

Per snipped-for-privacy@optonline.net:

I used to hang out at a beach near the yacht harbor next to the Ilikai hotel in Waikiki.

For years and years, the parking lot was just plain old dirt - light brown, somewhat dusty.

Then somebody got the bright idea of paving the parking lot with blacktop.

It made a huge difference. The parking lot area and adjacent beach went from being comfortable to being almost unbearably hot without a strong breeze to mitigate it.

So, unencumbered by any other knowledge, my money's on the white roofs...

Reply to
(PeteCresswell)

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I think they should paint the roads white, plant more trees and grass.

I was amazed with my only light plane flight over the desert. You could feel everything, roads, tracks, etc. Bump bump.

Greg

Reply to
gregz

Color isn't everything. Use reflectivity index. Higher energy cost is also meaning more energy creation, more heat. The insulation under the roof is going to be the main factor.

Greg

Reply to
gregz

There is also a big difference in artificial grass vs natural.

Driving around the city suburbs, it's often a relief to drive through a heavy tree area. Seems 15-20 degrees cooler.

Greg

Reply to
gregz

Was that based on stock white shingles or shingles painted white? Because surfaces painted white reflect roughly 90% of the sunlight, while regular white shingles reflect only 10%.

Reply to
larrymoencurly

The difference between light reflecting off a mirror and light reflecting off a white roof is the difference between "specular" reflection and "diffuse" reflection.

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Here's an example of \"specular\" reflection (off the cold calm water of Icy Bay, Alaska).

Reply to
nestork

The last bit about reflecting heat back into space is true. But because roofs are so small the effect is insignificant.

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Reply to
harry

You can easily tell the difference with white cars and black ones in the sun.

Reply to
harry

There used to be a nice breeze. Until they built the Ilikai which blocked the trades. Ala wai Harbor was much more comfortable before the Ilikai. For that matter, all of Honolulu was much more pleasant pre-high rise.

Reply to
dadiOH

Then explain why when the experiment was actually done in FL, using white shingles vs black, it only made a few percentage points difference in AC energy usage for occupied homes. And then factor in that the percentage of the earth's surface that is covered by roofs is negligible compared to the total surface.

Reply to
trader4

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Igloos are built with white roofs and they remain very cool inside. :-)

Reply to
willshak

Maybe thats what Limbagh told you but reradiation into space is an actual physical phenomena.

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Reply to
George

Someone should try black roof igloo. I propose a government study. about $5.5 million for start, and cost over runs and all. End up being about 20 million by the end of the year.

Christopher A. Young Learn more about Jesus

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Igloos are built with white roofs and they remain very cool inside. :-)

Reply to
Stormin Mormon

I've seen many model homes around Houston boasting energy saving features and they don't have white roofs so I think that proves you right. Our typical summer days are 95F but two or so years ago, we often had 102F summer days.

Reply to
Doug

Your recollection of the study's findings is not completely correct. You're right that in its initial testing of unoccupied homes, it found an approximate 10% energy savings using a white roof. But it also found that while occupying the homes increased energy usage overall, there was no change to the amount saved by the lighter roofs:

"Additional monitoring took place over a month long period with the homes occupied, but the thermostat set points were kept exactly the same as in the unoccupied monitoring period. Although average cooling energy use rose by 36%, analysis indicated no decrease to savings or demand reduction from the highly reflective roofing systems. The added heat gains from appliances and people increase cooling system run-time, with longer periods for the duct system to exchange heat to the often hot attic space."

And the study's conclusion:

"In summary, this evaluation strongly confirms the energy-saving benefits of using more reflective roofing systems in Florida. Selection of colors with higher solar reflectance will result in tangible cooling energy savings for customers. This is particularly true for roofing materials such as tile and metal which are currently available with solar reflectances of 65%-75%. The selection of reflective roofing systems represents one of the most significant energy-saving options available to homeowners and builders. Such systems also strongly reduce the cooling demand during utility coincident peak periods and may be among the most effective methods for controlling demand."

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Reply to
Moe DeLoughan

Figures someone would drag Limbaugh into the mix. Does Rush write and publish Discover Magazine and/or the cited studies?

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Reply to
trader4

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