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
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?
“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/
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?
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.
Your tax dollars at work, but that’s Ok, it’s all your fault, remember?
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.
Great
I need to replace my roof can I get Obama to pay for it… out of his own pocket?
They got funding for this?
“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.
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.
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)…
Early man had “green roofs”. They got rid of them because they were tired of bugs falling on their heads.
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.
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.
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…
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.
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.
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.
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/
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.
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.
@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…
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.
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.
There is a reason why plants are green.