White roofs three times as effective as green roofs
From Lawrence Berkeley National Laboratory and some members of the BEST team comes this surprise.
“We conclude that the choice of white vs. extensive green roof should be based on the environmental and societal concerns of the decision-maker. If global warming is a major concern, white roofs, which are around three times as effective at cooling the globe as green roofs, will be the preferred choice. On the other hand if the local environment is a primary interest, green roofs will be preferred. Of course, stormwater management may be a decisive factor in favor of green roofs, particularly in the presence of strict local stormwater regulations.”
The paper:
Economic comparison of white, green, and black flat roofs in the United States Julian Sproul,Man Pun Wan, Benjamin H. Mandel, Arthur H. Rosenfeld
Highlights
• The life-cycle costs of white roofs are less than those of black roofs.
• Green roofs are more expensive over their life-cycle than white or black roofs.
• Green roofs’ high installation/replacement costs outweigh their long service lives.
• Per unit area, white roofs cool the globe 3× more effectively than green roofs.
• Dark roofs should be phased out in warm climates for public health purposes.
Abstract
White and “green” (vegetated) roofs have begun replacing conventional black (dark-colored) roofs to mitigate the adverse effects of dark impervious urban surfaces. This paper presents an economic perspective on roof color choice using a 50-year life-cycle cost analysis (LCCA). We find that relative to black roofs, white roofs provide a 50-year net savings (NS) of $25/m2 ($2.40/ft2) and green roofs have a negative NS of $71/m2 ($6.60/ft2). Despite lasting at least twice as long as white or black roofs, green roofs cannot compensate for their installation cost premium. However, while the 50-year NS of white roofs compared to green roofs is $96/m2 ($8.90/ft2), the annualized cost premium is just $3.20/m2-year ($0.30/ft2-year). This annual difference is sufficiently small that the choice between a white and green roof should be based on preferences of the building owner. Owners concerned with global warming should choose white roofs, which are three times more effective than green roofs at cooling the globe. Owners concerned with local environmental benefits should choose green roofs, which offer built-in stormwater management and a “natural” urban landscape esthetic. We strongly recommend building code policies that phase out dark-colored roofs in warm climates to protect against their adverse public health externalities.
The paper is open access, and can be read here: http://www.sciencedirect.com/science/article/pii/S0378778813007652
h/t Steve Mosher
And then immediately below that heading is a picture of City Hall in Chicago where, of course, they suck at solving anything.
They have their phoney baloney jobs.
begins with Al Gore:
4:42 VIDEO: Bloomberg TV: Calculating Economic Risk of a Warming Atmosphere
Oct. 1 (Bloomberg) — Billionaire Tom Steyer, former U.S. Treasury Secretary Hank Paulson and New York Mayor Michael Bloomberg, founder and majority owner of Bloomberg News’s parent Bloomberg LP, have joined forces to fund a study to calculate how much economic risk American industries and communities face from a warming atmosphere and more extreme weather patterns… Bloomberg’s Edward Robinson reports.
http://www.bloomberg.com/video/calculating-economic-risk-of-a-warming-atmosphere-K9AGeiK9Sx2WFNWUTRzuLg.html
And a good thing too. 😉 It helps with the heating as opposed to the main thrust of Mosher’s link about saving on AC. Not all cities are the same.
Mike McMillan also note my bit about white painted buildings in warmer climes. My main point about the London is the bricks used are not white but reddish. Many roofs are black slate.
If you are not making a political statement with your roof, you are a bad citizen.
Hmmmmn.
So, the impact will be felt as either increased radiation gains (dark roof in summer adds to cooling bill),
Or dark roof leads to increased radiation gains which reduces heating needs in winter,
or increased radiation losses (white roof in summer leads to increased reflection of solar energy – if kept clean and pure as noted above) and thus reduces cooling energy needs in summer,
or a ever-changing color photoelectrically-controlled roof which changes day-by-day but can’t be built yet and needs power to run and more maintenance dollars when it gets dirty or breaks,
or a dark roof increases heat absorbed and melts snow and ice which leads to reduced weight loads in winter which leads to reduced building construction costs…,
or a “living green” roof leads to very, very, very heavy NEW loads which increases construction costs and building maintenance costs, fire ant dangers, live load weights (water + soil + soil/water barriers + “garden edge” treatments + lawn mower and goat expenses and goat removal expenses and goat manure removal expenses and sewage and water drainage expenses ….
Hmmmn.
Why don’t we LET THE BUILDING OWNER DECIDE WHAT SHE WANTS FOR HER BUILDING in that city at that location in that climate at that site for that architecture and that purpose?
Here is a good article by a gentleman who has written a bit about wall street and in this case erosion on Nantucket and Malibu.
http://www.vanityfair.com/society/2013/08/end-of-malibu-nantucket-erosion
Having spent some time myself on Nantucket, I note that the roof of almost every building are covered by cedar shingles that are covered with thick (green) moss as the humidity and other factors play a role in that particular climate. That said, the erosion issue on Nantucket and elsewhere seems to be another bailout for the fools (who expect the rest of us to pay for it) that built in an area subject to normal weather patterns. By reinforcing their little piece of heaven, others may incur damage as the above article touches upon.
Where did my raise go?
We spent it on global warming
Oh ah Thanks I guess…
Wonder why incomes are stagnant. Higher energy cost. Increased money spent on compliance. Insurance mandates. It all adds up and it the money to pay for it comes from somewhere.
kenw links to an article where the government claims ownership of rainwater so you can’t collect it. Where I live in Walla Walla, WA they tax us for hard surfaces and the water that runs off our property.
Jimbo says: January 31, 2014 at 12:07 pm
There are many people living under corrugated sheets who feel the force of heat every day. What they need are fans and ACs not this tripe.
Jimbo, your stuff is usually pretty sharp, so I must query if you have ever spent any time living under a corrugated iron roof. On a sunny day you can turn your face towards the underside of the roof and feel the heat radiating down. And such buildings usually come fully equipped with gaps between the floor boards and wall weather boards, and with gaps around the eaves between wall and roof. It is long way from there to air-conditioning!
White paint on the roof really helps, and we often do it on animal housing. In fact in an uninsulated partly painted animal house you can pick where the job is up to on the roof by walking along the shed inside. But then, the trick is keeping it clean, or repainting it frequently.
But where else shall we play lawn squash if Farnsworth can’t drive us to the country club? Pshhh. Uncouth provincials.
I guess you have to register with Sciencedirect to get the paper – not coming up as OpenAccess for me. I’d be keen to take a look at it, not least because as a humble blogger I looked at this issue a while back and came to the conclusion that a white roof was better from the viewpoint of weather station siting (if you were going to put a weather station on a roof):
http://diggingintheclay.wordpress.com/2010/07/17/thermal-absorption-a-black-and-white-and-green-issue/
“The original point of this NASA research was to look at ways of using vegetation to mitigate the heat within cities, but the final sentence in the abstract of paper by Gaffin et al suggests an additional purpose:
“These roofs should be superior to other urban rooftops as sites for meteorological stations.”
My first thought was God forbid! This crude comparison of a small portion of their data shows that choice of subsurface depth and even plant type could result in a station that, like the Queens green roof, is no different in terms of average temperature than a black roof. On the other hand the other two stations do show a reduction in average temperature and could be viewed as an improvement. Clearly strict adherence to ‘green roof weather station’ design guidelines would be important, but isn’t that the case anyway with set up of weather stations?”
here are some facts for you, 44C here today. I know of some black roofs in my location. Oh and yes, a complete no brainer, black cars are also popular.
From Lil Fella from OZ on January 31, 2014 at 7:04 pm:
Ouch, that could cause you significant lower back pain sooner or later. Have you considered reduction surgery?
Green/White – they don’t know Jack Schitt, but do know his sister Pisa.
White roofs three times as effective as green roofs
Total hoakum & more stupidity from Mosher! Neither has any effect on global climate. 3x zero is still zero!!! Roofs make up, what, 0.000000001% of the globe and they think changing the color of them is going to have any effect at all! BWAAAAHAHAHAHAHAH
Anyways, black roofs probably save more energy than white roofs, because most places have higher heating than cooling requirements. So how could a white roof be more energy efficient?
[JJ is an existing user-id, in use before you registered. Please choose another. Mod]
markx says:
January 31, 2014 at 6:08 pm
Jimbo says: January 31, 2014 at 12:07 pm
There are many people living under corrugated sheets who feel the force of heat every day. What they need are fans and ACs not this tripe.
Jimbo, your stuff is usually pretty sharp, so I must query if you have ever spent any time living under a corrugated iron roof. On a sunny day you can turn your face towards the underside of the roof and feel the heat radiating down.
________________________________________________________________________–
Spent 2 years under a corrugated roof. AC was like Heaven X 20
and forgot to mention that one day last summer it hit 46 Deg Celcius
Other JJ –
I have asked you five times now to play by Anthony’s rules and pick another handle. Moderators have contacted you with the same request.
WTF does it take for you to be a decent person?
JJ
@nicholas tesdorf January 31, 2014 at 2:09 pm:
“In generally warm climates like Australia, white roofs reflect heat in hot weather and fail to emit heat in cooler weather.”
I can go that one better. I worked in R&D with hot runner molds in which the cores (male part of the molds) were highly polished high-chrome steel. Without the polishing the cores emitted normally. But when polished OHMYGOD the emissivity dropped to basically zero, even at 420°F. No radiant heat at all. We even hired in infrared cameras so we could read the temp for hot and cold spots. Not a BLIP. The cores were invisible in the infrared. No emissivity at all.
And lest you wonder if there was convection – NO. One could put one’s hand anywhere around it and NOTHING was felt – total ambient temp. Even 1/32 inch away NOTHING was felt from a 420°F surface. And conduction? No again. Not until one actually TOUCHED the core. And THEN, OUCH!!! ***
The polish seemed to – if anything – reflect the heat back in, acting like a heat mirror. No joke..
So I would recommend someone check out REALLY shiny silvery roof coatings. I am certain they will compete with ANY of the others quite well. They would reflect sunlight back out and internal heat back IN. Or keep it in. That reflecting idea is just my conjecture, though it seemed to fit the facts. It is even possible that insulation would not be necessary – or really help if it was used,
Of course, you’d need to keep it very clean for best performance, And with snow? Not sure – but worth a look see! But then the other coatings have that same caveat.
*** We used the dreaded freon as a spray to deal with such burns, which were common. One poof of freon is the BEST treatment for burns EVER. But the ozone hole idiocy ended THAT.
RichardLH.
Before you lay odds you might want to read some things. case studies. field studies.
http://www.coned.com/newsroom/pdf/Columbia%20study%20on%20Con%20Edisons%20roofs.pdf
http://heatisland.lbl.gov/coolscience/cool-science-cool-roofs
http://www.onsetcomp.com/learning/application_stories/cool-roof-case-study
and many more
@nicholas tesdorf January 31, 2014 at 2:09 pm:
“Dark roofs emit and absorb heat more readily and in cool climates like northern Europe where incoming radiation is low even in summer, they produce worse internal conditions. The dark roofs also deteriorate faster under UV radiation and need replacement sooner. Snow cover, highly insulated roofs and vegetated roofs improve insulation and reduce heat transfer and snow reduces radiation. This improves internal conditions. The effect on the outside environment is minimal, but the effect on the conditions for inhabitants is very large.”
That last is not just something to pass off lightly. If the internal condition effects occur it is because heat is not flowing out of the roof. That means that insulation is occurring.
The “heat transfer” is a measure of “heat flow”, and it is the total heat FLOW that is important. When heat does not flow through a material or series of materials, that means the heat is NOT being released into the atmosphere. If heat flows OUT of buildings through the roof (which is the route for most heat flow losses), then that heat MUST be being added to the atmospheric heat energy content. It is measurable, even if it may often or always be negligible in a climate sense. But I don’t think it IS negligible, not when many thousands of buildings are losing heat to the atmosphere within a city. The heat losses add up. They WILL contribute to the urban heat island effect. The total heat flow will dissipate with distance, but it still exists. Especially when met stations are on rooftops, oy vey! The nearby buildings are warming that met station up.
“Yep, only where cooling is your issue. What about Scotland, Northern England, Canada et al? Higher heating bills due to white roofs?”
Actually not. But, In some of those places a green roof might be better.
But instead of guessing
just go search the literature
http://www.coolrooftoolkit.org/
Damn, this makes it even more complicated for the climate modellers what with the reflective properties of black, white, green, brindle, pink, purple, brown, slate and etc colored roofing reflective properties acting as still another forcing on the modeled global temperatures.
No worries! Nothing that another couple of hundred millions of the public’s hard earned thrown the climate modellers way can’t fix.
[ sarc/]
bill_c says:
January 31, 2014 at 1:27 pm
@ur momisugly Steve Mosher – how far down wind of a city can we see UHI effects?
Depends on
1. the strength of the wind. anything above 7m/sec and you wont have any UHI
2. the surface roughness
3. the time of day.
4. the strength of the UHI
5. the surface type of the land outside the city. forest/bare soil.. etc
For a clue put a thermometer over an asphalt parking lot.
The put another thermometer 15 feet away from the lot.
How far away from the lot do you have to go before the effect is zero.
Interesting stuff
http://www.fs.fed.us/psw/programs/cufr/products/11/psw_cufr68_EffectsTreeCoverOnEmissions.pdf
Question: do you sit 10 feet from the campfire?