Study: Green roofs suck at solving global warming

White roofs three times as effective as green roofs

Green roof of City Hall in Chicago, Illinois.

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

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127 Responses to Study: Green roofs suck at solving global warming

  1. Dodgy Geezer says:

    No shit, Sherlock?

    … Dark roofs should be phased out in warm climates for public health purposes…

    However, they should be extended in cold climates. It is also a good idea to open windows if you have a lot of people in a room and the weather outside is clement. If you are in a high building make sure that no one falls out.

    During a gas attack it is wise to seal all channels to the outside air, and wait for the wind to disperse the agent.

    Can I have a grant for writing this kind of stuff?

  2. kenw says:

    “Green roofs” pose a problem in areas that have deemed that the rainwater that falls on your own property to be public property.

    http://healthfreedoms.org/2011/12/27/collecting-rainwater-now-illegal-in-many-states-as-big-government-claims-ownership-over-our-water/

  3. David, UK says:

    From a purely local point of view it makes sense. Buildings would be more comfortable in summer with less dependency on air con. Globally though? Meh. What is three times F-all?

  4. Col Mosby says:

    You’d think a place as quasi-tropical as Florida would have figured out long ago that white
    shingles are better than black, which you see everywhere. Another ( bigger) waste of energy is
    the building code in Florida that allows ductwork to be entirely contained within the “attic.:”
    That attic hits 145 degrees about 8 months of the year. And Florida’s Govs in the past have
    trumpeted “energy saving” as a goal. Stupid jerks.

  5. Alan Robertson says:

    Your tax dollars at work, but that’s Ok, it’s all your fault, remember?

  6. Betapug says:

    Believe there is a free trial distribution of white roofs underway in much of the US at the moment. Not sure if this is government funded or not.

  7. Gail Combs says:

    Great

    I need to replace my roof can I get Obama to pay for it… out of his own pocket?

  8. Jimbo says:

    They got funding for this?

  9. RichardLH says:

    “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.”

    OK. Gets out calculator. Works out total area of ‘roofs’. Works out total area of Land Surface (we’ll just ignore the Water area for now – we only need a rough approximation to start with and anyway that wet stuff is too difficult to ‘roof’). Divides one by the other and, because the calculator I’m using is fixed point display, gets = 0.

    Conclusion even IF global warming is a major concern, whilst there may be impacts on the individual structures that have benefits, the contribution to the total figure will be = ~0 (or very, very close to it).

    Thanks for playing.

  10. kenw says:

    Col: If your attic is hitting 145 you have other issues. A properly ventilated attic should never be more than a few degrees warmer than the outside air.

  11. rgbatduke says:

    From a purely local point of view it makes sense. Buildings would be more comfortable in summer with less dependency on air con. Globally though? Meh. What is three times F-all?

    Amusingly so very true. And yet, if one considers the surface area of tarmac roadways, it is actually nontrivial. Well, ok, it is still pretty trivial compared to the total area of just the land surface, but it’s a BIG trivial number, and there is little doubt that it and black roofs contribute mightily to LOCAL warming in cities, a.k.a. the UHI effect.

    UHI corrupts current estimates of global warming by boosting poorly sited urban thermometers in ways that the primary temperature products do not seem to accurately correct for. So if by promoting white roofs and whitewashed roadways and developing white grass for lawns and maybe even just covering everything with white paint or aluminum foil in cities, we can lower urban temperatures, it will have an entirely disproportionate effect on global temperature estimates with their large occult UHI component. Basically, we need to paint the ground and everything on it white everywhere within half a kilometer of an official weather station. That would help a lot.

    Next: How we can completely cancel global warming by whitewashing the surface of the planet to emulate glaciers (at a cost of only ten quadrillion or so dollars)…

  12. philjourdan says:

    Early man had “green roofs”. They got rid of them because they were tired of bugs falling on their heads.

  13. Jimbo says:

    We strongly recommend building code policies that phase out dark-colored roofs in warm climates to protect against their adverse public health externalities.

    I’m in a hot and sunny clime with a red roof. Should I visit the doctor? What an utter waste of money.

    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.

  14. MJ says:

    It is amazing to me how much money is spent by “science” for things that people with common sense already know, or could care less about.

  15. JIm Sorenson says:

    And when the cold lingers, will we all be given permission to paint our roofs black and be reimbursed for it by our government? Just asking…

  16. TomRude says:

    Geeser, in cold climate (i.e. high latitude) or during winter, the sun rays are low and thus would only marginally warm a black roof vs a white roof.

  17. RichardLH says:

    rgbatduke says:
    January 31, 2014 at 12:04 pm

    “there is little doubt that … black roofs contribute mightily to LOCAL warming in cities, a.k.a. the UHI effect.”

    Sorry for the edit but roads are a different question.

    Hmm. I’ll lay you odds that the vertical surfaces contribute more to the total UHI than the roofs do.
    Especially if you take into account all the other flat bits, (excluding roads, pavements if you wish), parks, etc. at ground level.

    That’s why heat sinks often have large vertical areas in them, much better at transferring energy to the air.

  18. Walter Allensworth says:

    Does the study consider the CO2 removed from the air by plants on green roofs and how that will reduce carbon forcing? I didn’t see that in the bullets anywhere.

  19. Chris4692 says:

    Unfortunately the article is apparently free only to those who are institutionalized, so I cannot evaluate what they included, what they missed, and what their assumptions were. Green roofs are promoted around here more for their rainwater effects than energy savings so the conclusions don’t seem greatly off from what I would expect. I wonder if (or how) they included the extra structural costs of the green roof.

  20. JJ says:

    This annual difference is sufficiently small that the choice between a white and green roof should be based on preferences of the building owner.

    Newsflash skippy: The color of the roof (white, green, black, purple, whatever) should be based on preferences of the building owner because its is his damn building.

    That truth lies beside the fact that that the annual difference in “cooling the globe” between those roofs and any other kind of roof is sufficiently small that you arrogant %^&*tards need to find another pin upon which to hold your cotillions.

  21. Dodgy Geezer says:

    @TomRude

    Geeser, in cold climate (i.e. high latitude) or during winter, the sun rays are low and thus would only marginally warm a black roof vs a white roof…

    Why, thank you, Rude Tom! That is an important insight.
    Tell you what – let’s put in a proposal to visit lots of tourist spots around the world at different latitudes, and measure the effect of painting the walls black and white. We can go halves on the grant…

  22. Apoxonbothyourhouses says:

    This is the pseudo scientific $hit which gives academia a bad name and demonstrates monumental ongoing insensitivity as to how academics use our tax dollars. As if a few green roofs are significant compared to millions of hectares of pastureland. Having said that, it is the ivory tower person who approved the project who most needs to be dragged into the real world where poverty is all too common.

  23. mib8 says:

    heh. I recall some hippie dippie solar energy books from the 1970s concluding that “elm leaf green” was surprisingly absorbing more energy than flat black in their experiments.

    OTOH, I recall a History Channel bit (when they weren’t doing ancient aliens 24/7) about the development of the lawn: English greenswards, enclosure, sheep, importation of clover and such (for the grazing animals which weren’t doing well on the local plants), Shenandoah Valley bluegrass… that a grass lawn reduced temperatures… as compared with what alternatives I did not catch.

    Then again, if I were wealthy and stuck in an over-populated, over-crowded city, I’d want my penthouse to have some live greenery. (Similarly, due to fire hazard in such over-crowded environments, I’d want the building to be mostly concrete and steel. With other measures where earth-quakes are common.)

    I once lived in a house built in the 1940s. They thought a course of cinder-block was great insulation and it needed no more in the walls. I could feel the heat being sucked out of me in the winter. Similarly, many builders in Florida are just now beginning to catch on to the merits of insulation and attic ventilation.

    Still, as a general rule, people should be able to build their homes pretty much as they wish and can afford without being attacked by the code nazis and permit fascists.

  24. DesertYote says:

    There is a reason why plants are green.

  25. crosspatch says:

    “Per unit area, white roofs cool the globe 3× more effectively than green roofs.”

    An acre of white roof has about the same impact on climate as an additional acre of ice. With the deployment of additional acreage of white roofs, particularly at lower latitudes, we could see it causing a climate response much like what would be expected from increased glaciation. Seriously. If we get all “cool roof” in the US and Europe, it could potentially TRIGGER another glacial episode.

  26. RichardLH says:

    Steven Mosher says:
    January 31, 2014 at 12:16 pm

    “The impact while small in degress C, has the benefit of saving money.”

    That may well be true, but I will lay you any odds that the contributions from the vertical surfaces outweighs all of that combined. They are just so, so much more efficient at transferring energy to the air. Think heat sinks and radiators. We don’t build them flat for a good reason.

  27. Dodgy Geezer says:

    4WIW, I suspect that the most important issue with a roof is whether it’s cheap and easy to build, whether it functions properly in protecting the house underneath it, and whether it lasts.

    Those three parameters will have been optimised over hundreds of years for the different conditions and available raw materials in most human habitations – thousands of years in some cases.

    I’m pretty sure that requiring a different roof coating to the one commonly used in an area would cause one (or more) of those parameters to be sub-optimal.

    But hey, if there’s a grant involved…

  28. hunter says:

    One of the leading climatocract wrote about this years ago.
    I beleive it was Sec. of Energy Chu:
    “Today, U.S. Energy Secretary Steven Chu announced a series of initiatives at the Department of Energy to more broadly implement cool roof technologies on DOE facilities and buildings across the federal government. As part of the effort to make the federal government more energy efficient, Chu has directed all DOE offices to install cool roofs, whenever cost effective over the lifetime of the roof, when constructing new roofs or replacing old ones at DOE facilities. Additionally, the Secretary has also issued a letter to the heads of other federal agencies, encouraging them to take similar steps at their facilities.

    “Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change,” said Chu. “By demonstrating the benefits of cool roofs on our facilities, the federal government can lead the nation toward more sustainable building practices, while reducing the federal carbon footprint and saving money for taxpayers.”

    http://newscenter.lbl.gov/news-releases/2010/07/19/cool-roofs-offset-carbon-dioxide-emissions/

    In places witha lot of rain, green roofs are problemtaic due to the rain water management challenges: Extra structure for the roofs, water proofing, erosion resistance, irrigation for plants between rains, etc.

  29. David'93 says:

    JJ says “Newsflash skippy: The color of the roof (white, green, black, purple, whatever) should be based on preferences of the building owner because its is his damn building.”

    Best point of the day!

  30. bill_c says:

    RichardLH,

    I’d take your odds. First it’s an awfully dense city that has more vertical surface than horizontal. And I think your reference to heat sinks is true only because they have large vertical surfaces to increase total surface area/volume where horizontal surface area is constrained. It’s the total surface area that matters. In that vein a city with lots of tall buildings and 100% paved/roof area probably has more UHI than the same city with short buildings, until it starts creating its own convection cells.

  31. bill_c says:

    hunter,

    and was criticized by the rest of the climatocracy for daring.

    dodgy geezer,

    that doesn’t explain asphalt shingles. I think the primary reason for the shingle shape is aesthetics/ imitating slate/tile/wood shingle designs…..not because that design is the most efficient for the asphalt material (tho it’s not bad)

  32. Jimbo says:

    Steven Mosher says:
    January 31, 2014 at 12:16 pm

    The impact while small in degress C, has the benefit of saving money.

    http://www.theatlanticcities.com/design/2012/04/just-fraction-more-white-roofs-could-have-huge-global-impact/1764/

    Yep, only where cooling is your issue. What about Scotland, Northern England, Canada et al? Higher heating bills due to white roofs?

    OK many countries in hot climes paint their walls white. London is littered with dark building absorbing nice heat for a reason. Maybe I’m wrong here and stand to be corrected.

  33. Berényi Péter says:

    Why, sane people on warm sites choose white since millenia and put plants into the garden where they belong. One does not need a PhD to figure that out.

  34. RichardLH says:

    bill_c says:
    January 31, 2014 at 12:47 pm

    “I’d take your odds. First it’s an awfully dense city that has more vertical surface than horizontal. And I think your reference to heat sinks is true only because they have large vertical surfaces to increase total surface area/volume where horizontal surface area is constrained”

    You may well lose though. It’s all down to energy transfer to the air. Even if the area is smaller, the efficiency of transfer is so much higher when you can use convection to carry away the heat.

    Flat surfaces are OK, but quite a long way down in efficiency terms. Radiators might have been a better example rather than heat sinks.

    The sun is also likely to illuminate the vertical surfaces better as well. Only on one side of the building may be. But outside the tropics very important surfaces.

    And as for leakage from inside the building – no contest. Walls, windows, etc. every time.

  35. Jimbo says:

    From Mosher’s link.

    If you combined all of the world’s urban areas into one dense nugget of urbanity, it would cover about 2 million square kilometers, or 1.3 percent of the land area of the planet. About 60 percent of that – roughly the size of California and Texas combined – is made up of pavement and rooftops.

    These roads and roofs can be problematic surfaces. Often dark in color, they soak up sunlight, increasing the temperature of the building and surrounding area in what’s known as the urban heat island effect. This in turn contributes to a vicious cycle: the hotter a city feels, the more we energy we tend to use to cool it down, which leads to more greenhouse gas emissions, which contribute to climate change, and so on.

    http://www.theatlanticcities.com/design/2012/04/just-fraction-more-white-roofs-could-have-huge-global-impact/1764/

    It depends on where your city is. Some buildings need central heating in the summer. The article assumes all cities need urgent summer cooling. LOL. Tell that to Glasgow and Edinburgh.

  36. kadaka (KD Knoebel) says:

    kenw said on January 31, 2014 at 12:03 pm:

    Col: If your attic is hitting 145 you have other issues. A properly ventilated attic should never be more than a few degrees warmer than the outside air.

    So far here in central Pennsylvania in winter, where we’ve broken decades-old records with outside temperatures of single-digit and even negative numbers (°F), your idea of “properly ventilated” is frightening.

    It might work for “advanced” future construction methods, where the real house is a flat-roofed properly insulated and sealed “eco-box”, to which a traditional-looking lightweight roof structure is mounted for shedding snow and rain. If a hurricane or tornado gust rips it out of the breakaway mountings, the reinforced real house remains. Add a weathertight roof hatch to use the shell space for storage. Then your attic can be as ventilated as you want, although preferably dry. The shell space would also be good protection for your AC or heat pump central condenser unit. And perhaps a small pot farm.

  37. Andreas says:

    And when it rains too much followed by a freeze and snow, how ever will it withstand the extra weight of all that water?
    The mall that collapsed in Riga, Latvia didn’t it have one of those green roofs and probably had too much weight in soil water??

  38. u.k.(us) says:

    Probably should have read to comments first, but the picture in the post comes out of my county taxes.
    Compare that “green space” to the heat loss/gain of the buildings exterior.
    It’s Chicago, so no surprise.

  39. MarkW says:

    RichardLH says:
    January 31, 2014 at 12:11 pm

    ——

    Heat sinks have large vertical surfaces because that’s the only way to increase total surface area without taking up more real estate.

  40. Doug Huffman says:

    Green grass, sod, rooves are traditional here, with goats to trim the grass. Unfortunately a local business man has Service Marked the use of goats so local business now have shaggy rooves.

    We also have hundreds of acres of common water reed Phragmites that thatches a roof to R 40(!) with nearly unlimited lifetime with proper maintenance.

  41. MarkW says:

    RichardLH says:
    January 31, 2014 at 12:57 pm

    ——

    The convection is so small that it isn’t worth considering. Most of the heat radiated by heat sinks is in the form of radiation anyway.

  42. bill_c says:

    RichardLH,

    I understand what you’re saying but remember we’re not talking about energy loss or gain from buildings (at least for UHI and roofs), we’re talking primarily about an albedo effect. At least for a white vs a black roof, where there’s no evapotranspiration, we’re just talking about the % of sunlight absorbed, and of course no combination of vertical surfaces can amplify the heat gain beyond 100% of the incident solar.

    Now, the building-level energy savings from installing a white roof doesn’t compete from retrofitting windows and walls for leakage in a tall building. Sure – but that’s apples and oranges here, unless I’m really not understanding the problem setup.

    Most of the increased energy absorption from a dark roof is going to be radiated and convected away to the atmosphere, contributing to UHI more or less depending on meteorological conditions…

  43. bill_c says:

    @ Steve Mosher – how far down wind of a city can we see UHI effects?

  44. Bob Rogers says:

    Here in the South (i.e, southern part of USA), we have fire ants. If you put dirt on your roof, fire ants will find it, because of the lack of predators. This might not be a problem, but they will burrow down through the dirt, and through the EPDM layer, and the roof will leak. Then you have to remove the dirt to fix the layer, and start spreading ant poison.

  45. Jimbo says:

    I lived in London for many years and I can never remember a time when I wanted air conditioning in my apartment, never. Sure it got a little warm a few weeks in SOME summers but I didn’t even think about a fan. It just doesn’t get hot for long enough to bother with. The only places with A/Cs are stores, diners, offices etc which are often ‘sealed’ (closed windows / doors) with bright lights and lots of machinery giving off heat.

    I never complained about the ‘heat’ in summer while walking in the street, never. I welcomed it sorely. ;-)

  46. hunter says:

    bill_c,
    Yes, and we skeptics pointed out that if AGW is so small as to be signficantly mitigated by white roofs, then AGW is not really a big deal. Of course we were dismissed as well.
    The key ingredient to credibility in the AGW community seems to be two part:
    1) The claim must come from an acceptable source, and the claim is nearly always paid for by tax payer grants or direct tax money
    2) The claim must never question or minimize the underlying crisis that the AGW movement believers require.

  47. R. de Haan says:

    BS, I prefer black roofs. White and Green, so out of date.

  48. Everybody knows that most roofs will be bi-racial in the future.

  49. markstoval says:

    Newsflash skippy: The color of the roof (white, green, black, purple, whatever) should be based on preferences of the building owner because its is his damn building.

    It is nice to see that there are those here who still believe in property rights. Damn nice.

  50. asybot says:

    That’s what a lot of buildings look like in Detroit (except from the bottom up)

  51. In generally warm climates like Australia, white roofs reflect heat in hot weather and fail to emit heat in cooler weather. This improves internal conditions generally. 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. The inhabitants can easily make their own decisions.

  52. kadaka (KD Knoebel) says:

    Just replace traditional roofing materials with LCD screens. Each panel can be a solid color, and they can make flexible LCD sheets so they could come as cut-to-fit roll roofing, so the roofs can be any color they want and can change as needed.

    Mandate them for new construction and roof replacements on non-historic buildings. It’ll be pricey, but as it’s for both energy savings and fighting global warming, I’m sure there’ll be a government grant and/or tax rebate program that’ll cover it. Just hand Barry O his pen so he can Executive Order it all into existence, mission accomplished.

  53. kenw says:

    @kadaka: obviously you are correct, I inadvertently assume warmer weather situations, such as we have here 11 months of 12.

  54. Berényi Péter says:

    For white roofs snow is the perfect material. It reflects sunlight, it is an efficient radiator in thermal IR and it is a great insulator. With global warming, as everyone knows, we shall never run out of it, because warming increases evaporation, which brings ever more precipitation, snow included, presumably. At least that’s how increasing snow extent is explained away.

  55. RichardLH says:

    MarkW says:
    January 31, 2014 at 1:18 pm

    “The convection is so small that it isn’t worth considering. Most of the heat radiated by heat sinks is in the form of radiation anyway.”

    Go tell that to the water radiators in my house. They work vertically and by convection as the major source of heat transfer.

  56. RichardLH says:

    bill_c says:
    January 31, 2014 at 1:22 pm

    ” understand what you’re saying but remember we’re not talking about energy loss or gain from buildings (at least for UHI and roofs), we’re talking primarily about an albedo effect.”

    I know. Think about this then. If you were to measure the temperature of a south facing black wall and a black drive against it, which do you think will get hotter and why? Assuming that we are talking about throughout the day and somewhere, say, at Lat 45 degrees N or S. Now over the whole year? See what I am talking about?

    Roughly more energy will fall on the wall than the roof, over most days. over most of the year. And it will still be cooler because the energy leaks away faster into the air from the wall. All that lovely vertical space moving the air faster.

    If you want to improve solid to air energy movement, you make as rough a surface as you can because the energy transfer is faster. The max is probably around where the shadowing of the ‘next’ vertical surface starts to become a significant influence on the input.

    IMHO anyway.

  57. Tamara says:

    While I agree that this study seems to be a verification of common sense, I think we should back off on ridiculing the academics. It is the moronic politicians who need studies like this. If they don’t get reports that say “Hey, tardo! Don’t do that! It’s a waste of money, and plus it is a really, really dumb idea!” Then, they go ahead and write laws that force us all to comply with the really, really dumb idea.
    I think we should be thanking these researchers for making this common sense part of the literature BEFORE we all either had to foot the bill for our own green roofs, or foot the bill for the subsidies for everyone else’s green roof.

  58. John F. Hultquist says:

    bill_c says:
    January 31, 2014 at 1:27 pm

    “. . . how far down wind . . .”

    A study for the Chicago region (I think) was done in the late 1940s or early ’50s but the emphasis was on the down wind rainfall, not temperature. Dust and chemicals from urban functions were greater years ago than now so there were many concerns. The better neighborhoods were often on higher ground away from the “Big City” (see Haggard, Merle) while the stock yards were down wind of the better neighbors.
    Anyway, one doesn’t have to go far from the built up area to escape the UH but other things farther away can be impacted.
    A couple of years ago the host of WUWT did a post on a car mounted data-logger that allowed you to do your own research on this topic for a city near you. Graphs and photos included:

    http://wattsupwiththat.com/2010/04/04/measure-uhi-in-your-town-with-this-easy-to-use-temperature-datalogger-kit/

    http://wattsupwiththat.com/2012/07/10/new-gadget-remote-wifi-temperature-humidity-data-logger/

  59. chris y says:

    Mosher’s linked article claims that a 1% increase in the surface albedo of 1.3% of the global land area (0.39% of the total global area) will result in a 0.07 C temperature drop. That amounts to an albedo change of 0.01*0.0039 = 39 ppm.

    Using a sensitivity of d(albedo) = 0.011 per degree C, I estimate 0.0035 C, a factor of 20 smaller.

    Also, a white roof requires much more maintenance to keep it white, compared with a dark colored roof. Anyone who lives in Florida near an ‘evergreen’ (ho ho!) live Oak tree understands this in spades.

    Ah well, when it comes to saving the world from too many carbon units, its the thought that counts…

  60. faboutlaws says:

    Obama can come to the rescue with some of his talked about presidential initiative. He can let his hair (roof) continue to go fully white. Maybe Jay Carney can help out by stealing the black shoe polish out of the WH. My dad always accused my mom’s immigrant step dad of using that stuff to keep his hair dark well into his eighties.

  61. Erny72 says:

    “…Owners concerned with global warming should choose white roofs, which are three times more effective than green roofs at cooling the globe…”
    WTF?
    Are the authors suggesting that thin air taxes, wind turbines, solar cells and a lot of overpaid United Numpties bureaucrats are all unnecessary because if we all erect a white roof we can cool the globe?
    Sounds like the problem of tackling climate change is solved, we just have to paint our roof white. BEWDY!

    …do I need to add, /sarc

  62. Dodgy Geezer says:

    @bill_c
    …dodgy geezer,
    that doesn’t explain asphalt shingles….

    Doesn’t it? I smell a grant coming on…

  63. pat says:

    Bloomberg to the rescue!

    31 Jan: Reuters: Michelle Nichols: United Nations appoints former NYC Mayor Bloomberg cities, climate change envoy
    U.N. Secretary-General Ban Ki-moon on Friday appointed former New York City Mayor Michael Bloomberg as his special envoy for cities and climate change, in a bid to build momentum ahead of a planned U.N. conference in September.Ban said Bloomberg will assist him in “consultations with mayors and related key stakeholders, in order to raise political will and mobilize action among cities as part of his long-term strategy to advance efforts on climate change.”…
    The U.N. role for Bloomberg – a billionaire philanthropist who left office last month – was reported by Reuters on Thursday.trueIn a statement, Bloomberg said cities had emerged as a leading force in the battle against climate change. His appointment as U.N. special envoy is for two years…
    Samantha Power, U.S. ambassador to the United Nations, was quick to welcome Bloomberg’s appointment, posting on Twitter: “Mayor @MikeBloomberg knows how to get things done. We need more leaders like him here @UN.”…
    Bloomberg has played a leading role in the C40 Cities Climate Leadership Group, an international group of mayors created in 2005 and dedicated to reducing greenhouse gas emissions. The C40 group, of which Bloomberg is president of the board, is to meet in Johannesburg next week…

    http://www.reuters.com/article/2014/01/31/us-climate-un-bloomberg-idUSBREA0U02Q20140131

    not a hint of the following in the above Reuters report:

    23 Jan: NYT: Carol Davenport: Industry Awakens to Threat of Climate Change
    The California hedge-fund billionaire Thomas F. Steyer, who has used millions from his own fortune to support political candidates who favor climate policy, is working with Michael R. Bloomberg, the former New York mayor, and Henry M. Paulson Jr., a former Treasury secretary in the George W. Bush administration, to commission an economic study on the financial risks associated with climate change. The study, titled “Risky Business,” aims to assess the potential impacts of climate change by region and by sector across the American economy.
    “This study is about one thing, the economics,” Mr. Paulson said in an interview, adding that “business leaders are not adequately focused on the economic impact of climate change.”
    Also consulting on the “Risky Business” report is Robert E. Rubin, a former Treasury secretary in the Clinton administration. “There are a lot of really significant, monumental issues facing the global economy, but this supersedes all else,” Mr. Rubin said in an interview. “To make meaningful headway in the economics community and the business community, you’ve got to make it concrete.”…
    Although many Republicans oppose the idea of a price or tax on carbon pollution, some conservative economists endorse the idea. Among them are Arthur B. Laffer, senior economic adviser to President Ronald Reagan; the Harvard economist N. Gregory Mankiw, who was economic adviser to Mitt Romney’s presidential campaign; and Douglas Holtz-Eakin, the head of the American Action Forum, a conservative think tank, and an economic adviser to the 2008 presidential campaign of Senator John McCain, the Arizona Republican.
    “There’s no question that if we get substantial changes in atmospheric temperatures, as all the evidence suggests, that it’s going to contribute to sea-level rise,” Mr. Holtz-Eakin said. “There will be agriculture and economic effects — it’s inescapable.” He added, “I’d be shocked if people supported anything other than a carbon tax — that’s how economists think about it.”

    http://www.nytimes.com/2014/01/24/science/earth/threat-to-bottom-line-spurs-action-on-climate.html?_r=0

    ——————————————————————————–

  64. Geoff Sherrington says:

    “Owners concerned with global warming should choose white roofs, which are three times more effective than green roofs at cooling the globe.” So say the authors.
    The only way the globe will warm or cool, if the experts are right, is by loss of radiation to space.
    I’ll be interested to read if the authors have accurately traced the energy path from roof to space to show net gain or loss.
    Seems to me, if they can do that, they are achieving more than the top climate modellers who have not been successful at that task.
    So, it’s a reasonable conclusion that the paper takes some short cuts and so it might not be correct.
    I’ve an open mind. Convince me I’m wrong & I’ll write a corrected post, with unreserved apology.

  65. Leslie says:

    I wonder about the snow removal process on a green roof like the Chicago City Hall’s. Where would one dump the excess snow?

  66. Andyj says:

    Edinburgh Scotland. The slate tiles heat up in the sun so they fitted extraction and a pipe to blow the warm air down amongst the congregation. Saving 40 percent of the cathedrals heating bill.

    Horses for courses eh?

    As goes this paper……. wtf???

  67. Andyj says:

    Ooops, sorry, Edinburgh Cathedral

  68. SadButMadLad says:

    Scientists work out why all the buildings in Greece are white. They are so clever are scientists. They must be gods they know so much. /sarc

  69. D.J. Hawkins says:

    kenw says:
    January 31, 2014 at 2:11 pm
    @kadaka: obviously you are correct, I inadvertently assume warmer weather situations, such as we have here 11 months of 12.

    Actually kenw, you were correct in the first instance. A properly constructed simple peaked roof over and attic area will have a opening in one or both gable ends and a continuous ridge vent, no matter the prevailing climate. The objective is to maintain the roof temperature as close as possible to the outside air temperature. In winter, if the underside of the roof is significantly warmer than the outside, any snow cover will melt from underneath during the day, and refreeze at night as temperatures drop. This leads to the formation of ice dams and can cause a tremendous amount of damage as water backs up below the shingles and penetrates the felt layer, causing damage to drywall ceilings and walls alike.

  70. clipe says:

    Now I know why my younger brother kept pigeons. Way ahead of his time, that lad.

  71. Mike McMillan says:

    Jimbo says: January 31, 2014 at 12:50 pm
    … London is littered with dark building absorbing nice heat for a reason. Maybe I’m wrong here and stand to be corrected.

    The reason London is dark is because it hasn’t gotten around to scrubbing off all that coal soot the way Paris has.

  72. Tom J says:

    I find it humorous that the title for this blog post is: ‘Study: Green Roofs Suck at Solving Global Warming.’ And then immediately below that heading is a picture of City Hall in Chicago where, of course, they suck at solving anything.

  73. M Simon says:

    Geeser, in cold climate (i.e. high latitude) or during winter, the sun rays are low and thus would only marginally warm a black roof vs a white roof.

    In cold climates roofs (on houses) are peaked. To keep the snow from accumulating.

  74. M Simon says:

    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.

  75. pat says:

    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

  76. Jimbo says:

    Mike McMillan says:
    January 31, 2014 at 4:08 pm

    Jimbo says: January 31, 2014 at 12:50 pm
    … London is littered with dark building absorbing nice heat for a reason. Maybe I’m wrong here and stand to be corrected.

    The reason London is dark is because it hasn’t gotten around to scrubbing off all that coal soot the way Paris has.

    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.

  77. Jimbo says:

    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.

  78. Gamecock says:

    If you are not making a political statement with your roof, you are a bad citizen.

  79. RACookPE1978 says:

    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?

  80. john says:

    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.

  81. troe says:

    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.

  82. Gary Jarnes says:

    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.

  83. markx says:

    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.

  84. HGW xx/7 says:

    But where else shall we play lawn squash if Farnsworth can’t drive us to the country club? Pshhh. Uncouth provincials.

  85. Verity Jones says:

    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?”

  86. Lil Fella from OZ says:

    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.

  87. kadaka (KD Knoebel) says:

    From Lil Fella from OZ on January 31, 2014 at 7:04 pm:

    here are some facts for you, 44C here today. (…)

    Ouch, that could cause you significant lower back pain sooner or later. Have you considered reduction surgery?

  88. Ed, Mr. Jones says:

    Green/White – they don’t know Jack Schitt, but do know his sister Pisa.

  89. JJ says:

    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]

  90. Steve B says:

    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

  91. Steve B says:

    and forgot to mention that one day last summer it hit 46 Deg Celcius

  92. JJ says:

    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

  93. Steve Garcia says:

    @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.

  94. Steve Garcia says:

    @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.

  95. Steven Mosher says:

    “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/

  96. ROM says:

    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/]

  97. Steven Mosher says:

    bill_c says:
    January 31, 2014 at 1:27 pm
    @ 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?

  98. Steven Mosher says:

    “chris y says:
    January 31, 2014 at 2:32 pm
    Mosher’s linked article claims that a 1% increase in the surface albedo of 1.3% of the global land area (0.39% of the total global area) will result in a 0.07 C temperature drop. That amounts to an albedo change of 0.01*0.0039 = 39 ppm.
    ###################

    and all while saving money.

  99. scarletmacaw says:

    RichardLH says:
    January 31, 2014 at 2:20 pm

    Go tell that to the water radiators in my house. They work vertically and by convection as the major source of heat transfer.

    Radiators work through both convection and radiation. Surface area is the main factor, and the radiator is vertical because it takes up less floor space. A horizontal radiator with the same surface area would work just as well in heating the room. In either case, convection is enhanced when a fan circulates the air.

    White roofs work well in the tropics to keep the house cooler, but, as others have pointed out, are worthless if they can’t be kept clean and white. Green roofs are even harder to maintain, and require a much sturdier construction beneath the soil, both in weight-bearing and waterproofing.

    Well-placed shade trees are a cheaper and easier to maintain solution in areas of sufficient rainfall.

  100. Annie says:

    We are living under a pale green corrugated roof atm. The outside temp. is in the high 30’s. Thank God for the A/C! First thing today the temp. was below 20C and we felt cold…there is a lack of insulation in the house. When will the average Australian house catch up with the vagaries of the climate here?! ( We are in Victoria).

    I miss our cosy little Yorkshire cottage; we could keep warm in winter and cool in summer without much trouble.

  101. norah4you says:

    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.
    WHICH Global Warming? Never happened in recent years. Measuring reflexion is one thing, but no computer program on Earth can measure 1 meter above ground and at the same time 1 meter under ground/water surface…..
    Btw. it’s close to 43 years since I had my Exam as a Systemprogrammer. Studied many other subjects over the years as well among them Mathematic, Mathematic Statistic and History plus some courses in Geology…

  102. Toto says:

    Which is better, white roofs or roofs covered with solar cells? (rhetorical question)

    This paper looked at the economics of some industrial roofs and it makes sense that a white roof would be better than a green roof economically. But how did the study determine that white roofs are three times more effective than green roofs “at cooling the globe”? Did they measure anything to get that conclusion? Should we extrapolate that and cut down forests and dig up lawns? How would a green grass roof and an green astroturf roof compare?

    This is from one of the links Mosher recommended:

    http://www.coned.com/newsroom/pdf/Columbia%20study%20on%20Con%20Edisons%20roofs.pdf

    Dark roofs typically have a low albedo, such as
    5%, meaning 95% of incident solar radiation is
    absorbed by the roof and transformed into heat
    energy. White roofs usually have rated albedos
    in the 75%–80% range, meaning only 20%–
    25% of incident solar radiation is absorbed.
    [...]
    It is important to note that the white and
    green roofs are achieving temperature
    reductions largely through two fundamentally
    different strategies: white roofs are reflecting
    most of the sunlight, whereas green roofs—
    although more reflective than black—are
    transforming the absorbed sunlight into water
    vapor through evapo-transpiration, also called
    “latent heat loss.” Green roofs do have a
    significantly higher albedo than black roofs. We
    have measured them as having an
    approximately 20% albedo.11 But this accounts
    for a smaller fraction of the cooling as
    compared to latent heat loss, which is an
    extremely powerful mechanism of heat loss in
    living systems, including the human body.

    An interesting finding is that the white
    and green roof surface temperatures are fairly
    close. In other words, green roofs are cooling at
    least as effectively as the most reflective white
    roof commercially available.

    The earth’s surface, the part which is not water or desert or ice, is mostly densely covered by green solar collectors (plants), little engines which influence the climate in ways not appreciated.

  103. Non Nomen says:

    Now I think it is time to consider mirrors on the roofs! But I suppose some environmentalists will soon find out that it is harmful for birds. If some ducks mistake that for water, well …

  104. Geoff Sherrington says:

    “Steven Mosher says:
    January 31, 2014 at 12:16 pm
    The impact while small in degress C, has the benefit of saving money.
    ………………..
    Are people making a case for conserving global energy OR local energy as within buildings?
    I thought the paper’s authors were pushing the former.
    It is not always that a white roof will save energy. If it results in local heating of air that has to be sucked into a nearby aircon unit’s inlet, it will cause a load. That is not a money-saving benefit. Property rights, good neighbour stuff and so on applies.
    Surely it is only a real saving if the global balance is affected in an energy-saving way. Otherwise, it’s not necessarily a saving, it’s just a redistribution. That in turns leads to arguments of what is good and what is bad. Excess heat can be a discomfort for people but an aid to edible plant yield. It’s surely far too big a consideration to be analysed in terms of roof size, shape, colour and abundance.
    Angels dancing on heads of pins?

  105. I put a green roof on my house. Corrugated, galvanized steel. Light green.

    Not done yet though. Still need to paint the disruptive patterns to confuse the aerial surveillance and sattelite imagery used by local government to extort higher rates from residents.

    P.S. Non Nomen Insects in have been observed on larger PV installations to be confused by the surface of the panels, causing them to deposit their eggs on the shiny surface, apparently believing it to be water.

  106. michael hart says:

    Dodgy Geezer says:
    January 31, 2014 at 11:44 am

    No shit, Sherlock?

    ‘Green toilets’ don’t do much to prevent global-warming either. I guess it’s just as well we haven’t had much for about a decade or two.

  107. RichardLH says:

    scarletmacaw says:
    January 31, 2014 at 10:18 pm

    “Radiators work through both convection and radiation.”

    I do rather know that you know. I will still contend that a radiator of the same area laid flat will be less efficient in transferring heat to the air than one placed vertically. The air speed on the top of the two arrangements is quite different.

    A flat object produces quite gentle air flows. A vertical one quite a fast ones.

    As I said above, if you wish to gain the most effective transfer of solid to air one would use the roughest surface in a ‘large’ sense as one could manufacture.

    This will allow the vertical surfaces to promote air flow which will then help to cool the flat portions. Like a set of cubes, of better still rectangles, placed on end. If you arrange such a surface so that the rectangles are randomly placed on the horizontal area you will allow the maximum surface area for energy to be collected especially outside of the tropics where the input angle for most of the day will be below the critical angle where the effective area of the horizontal surface exceeds that of the vertical one over the whole year. Cos and sin might help you work out the effective as opposed to actual surface areas involved when doing your calculations.

    If you achieve a surface which has larger vertical surfaces (i.e. rougher) , you will, in general, improve energy transfer.

    Please note that green roofs are mostly only useful for flat roofs and mainly for buildings that are made of reinforced concrete due to the large mass that such structures entail. There have been roofs constructed out of living grass, etc. but the extra cost of the reinforced roof structure needs to be taken into account.

    White roofs, as noted by others above, require continuous maintenance to remain effective.

    Lastly, the total area of roofs (as opposed to other flat collecting surfaces) is so minute that if will probably not show on most standard, fixed point display calculators as factor to be added.

    The only way the figure gets to be of interest is if you add in roads, pavements, parking areas, etc. to the mix.

    Then it might, just might, creep into the right hand side of such a calculator as a ……..01.

    The world is very big and we occupy such a small area of it. Now the Sahara Desert. If we covered that with shiny metal we could really gets some legs behind theidea. Don’t fly planes over it afterwards.

    IMHO

    Steve:
    I know there are lots of studies. Can you please point me to where they have taken into account the above comments?

  108. pochas says:

    RichardLH says:
    February 1, 2014 at 2:20 am

    “White roofs, as noted by others above, require continuous maintenance to remain effective.”

    Our church had an extensive area of plantings on the roof, and guess what? The roof membrane that kept the rainwater from invading the space below eventually leaked and a gargantuan mess ensued. The only solution was to take out the plantings and the soil below to allow access to the membrane to replace it. Very expensive. Personally, I would not consider a green roof knowing I faced that project in the future.

  109. J.H. says:

    I live in the tropics….. A white roof is the only one I’d have.

  110. ozspeaksup says:

    Bernd Felsche says:
    February 1, 2014 at 12:49 am

    I put a green roof on my house. Corrugated, galvanized steel. Light green.

    Not done yet though. Still need to paint the disruptive patterns to confuse the aerial surveillance and sattelite imagery used by local government to extort higher rates from residents.

    P.S. Non Nomen Insects in have been observed on larger PV installations to be confused by the surface of the panels, causing them to deposit their eggs on the shiny surface, apparently believing it to be water.
    ////
    Love the camo idea:-) I have a lightgreen corugated roof while the rust on one spots a start..I LIKE your idea a LOT .
    In Vic as the lady above.
    was under 20 but wouldnt say that was cold this am
    got to the 40+ late arvo, inside? was 35 and thats with a middlin high pitched roof and insulation..
    the house is wood and the WALLS have no insulation..if/when I can rip boards off and pack batts in there I bet its heaps better.
    last home old stone walls 12 ins thick winter inside got to 3c skillion roof and no insulation
    with batts? it didnt drop below 10c still cold but heaps better.

  111. Steve Keohane says:

    Steven Mosher says: January 31, 2014 at 10:13 pm

    bill_c says:
    January 31, 2014 at 1:27 pm
    @ 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

    So 2.2 MPH is called wind…and that mitigates UHI, Please!

  112. Jimbo says:

    Steve B says:
    January 31, 2014 at 9:19 pm

    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.

    As I type I have am under a corrugated sheet roof! Honestly.

    Maybe I should have been more precise in my hast and said that “people living under corrugated roofs” instead of “sheets“. The difference between the two can be plain sheets upheld by some light wooden beams and triangular roofs with a ceiling. The plain sheets are murder, the roofs with spacing allow for ventilation in the space created and thus you can’t ‘feel’ the heat being radiated down. Don’t worry I know about corrugated sheets.

  113. Jimbo says:

    Oooops! My last reply was meant for
    markx says:
    January 31, 2014 at 6:08 pm

  114. Jimbo says:

    markx says:
    January 31, 2014 at 6:08 pm
    ………….
    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!

    Not all corrugated abodes are in same or in the same country. ;-)

    My corrugated home is the left plain silvery colour (aluzinc) which I think is better for reflecting much of the heat compared to coloured sheets. On the other hand some people paint their with red oxide to give it a better look, while some go for different colours on factory painted sheets. My home is painted white. I personally would avoid dark colours due to the heat absorption. I also have an air-conditioner and fans in the bedrooms and living room, windows nearly always open with thick dark curtains with a light secondary back covering to reflect the sun’s rays a little. No floorboards just cool tiles. So markx, I do know a little about keeping cool under heat.;-)

  115. Coach Springer says:

    Cost is the key factor. Public health and local environment is a minor after thought. Or should be. Unless you are going to plant all your streets, sidewalks and parking lots, your roof top benefit available mainly only in a light shower anyway is pretty much entirely pointless. We’ve got a couple of green posturing roofs in the Midwest. How are those minimal benefits affected during dormancy. “Green” is an attempt to distract the mind, but it sounds like lighter color roofs makes economic sense.

  116. Latitude says:

    Dark roofs should be phased out in warm climates for public health purposes…..

    bite me…

    first they came for the roofs

  117. RichardLH says:

    Coach Springer says:

    ““Green” is an attempt to distract the mind, but it sounds like lighter color roofs makes economic sense.”

    For internal comfort, better roof insulation is likely to be cheaper and more effective. As are thicker walls and underfloor insulation.

    I used to live in a Cotswold Cottage. Big thick walls. Always cool in summer and, provided you kept the heating going, always warm in winter. If you let the heating stop though, it could take weeks to get it back to ‘normal’.

  118. Non Nomen says:

    “Our church had an extensive area of plantings on the roof, and guess what? The roof membrane … leaked and a gargantuan mess ensued.”
    I always thought a church is the right place for a mess…
    I personally live under a black roof that is made of some sort of moulded foam concrete(I think) and underneath it is hot in summer and cold in winter. I suppose that a reasonable insulation helps more than anything else.

  119. CaligulaJones says:
  120. Silver ralph says:

    So if the climate is warm, we should have white houses and roofs. Derrr, I think the Greeks knew about this some 3,000 years ago.

    Santorini village, Greece.

    I suppose they will be telling us next that is it rains a lot, we should have gutters. And if it snows a lot, we should have snow guards of the roof. And if it is very cold, we should insulate.

    Please forward a grant application form to this email address, because i could revolutionise town planning with all these brilliant ideas.

    /sarc.

    Ralph

  121. Silver ralph says:

    Oh, and a piece if advice for the greenies out there. If you plan on making a lovely green roof do calculate the weight of the rain it will accumulate, otherwise your attempt to save the planet will turn into a deadly disaster.

    Riga ‘green roof’ collapse.

    http://www.bbc.co.uk/news/world-europe-25045879

    As ever with green ideas, the fantasy sounds wonderful, while the reality is a catastrophe for everyone.

    Ralph

  122. Eric says:

    Did the study consider the difference in greenhouse gas emissions for HVAC between the white and green roofs?

  123. numerobis says:

    I’ve seen a few claims that you want a dark roof in winter. This will obviously depend on your locality, but in Montreal, you don’t have a choice: Mother Nature always paints your roof white in winter. There’s a couple weeks in spring and fall when you have the heat on but no snow on the roof; the rest of the time, your roof is either white by snow cover, or you hope your roof is white to keep the heat down. So, get a white roof!

    (I rent, so I have a dark roof, sadly.)

  124. RichardLH says:

    numerobis says:
    February 2, 2014 at 9:11 am

    “I’ve seen a few claims that you want a dark roof in winter. This will obviously depend on your locality, but in Montreal, you don’t have a choice: Mother Nature always paints your roof white in winter. ”

    Given the typical winter sun angle, the most effective solution is back walls, preferably behind glass. Only equator facing of course, the other walls should be white (reduces radiation slightly).

    Flat roofs have a very poor effective sun angle at that time of year and, as you note, do tend to get covered in snow.

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