White roofs are the most cost-effective option.

28 January 2014 — A report out of Lawrence Berkeley National Laboratory has found white roofs to be the most cost-effective option over a 50-year time span – ahead of green and black roofs – lending support to the notion that black roofs should be phased out.

“White roofs win based on the purely economic factors we included, and black roofs should be phased out,” said study co-author Dr Arthur Rosenfeld, a Berkeley Lab distinguished scientist emeritus and former commissioner of the California Energy Commission.

The report, Economic Comparison of White, Green, and Black Flat Roofs in the United States, will be published in the March 2014 edition of Energy and Buildings, but is now available online.

The research looked strictly at the economic costs and benefits of the three types of roof, though acknowledged that while there was a high installation cost to green roofs, they had additional environmental and amenity values that weren’t captured in the analysis. For example, rooftop gardens or green roofs can provide stormwater management, cool the roof’s surface and surrounding air, and increase aesthetic appeal.

“We leave open the possibility that other factors may make green roofs more attractive or more beneficial options in certain scenarios,” said Benjamin Mandel, a graduate student researcher at Berkeley Lab. “The relative costs and benefits do vary by circumstance.”

However, the report found that green roofs, unlike white roofs, did not directly offset climate change. White roofs were more reflective than green roofs, reflecting about three times as much sunlight back into the atmosphere. By absorbing less heat, white roofs were found to offset more of the warming effects of greenhouse gas emissions.

“Both white and green roofs do a good job at cooling the building and cooling the air in the city, but white roofs are three times more effective at countering climate change than green roofs,” Dr Rosenfeld said.

White roofs win on cost

Relative to black roofs, white roofs provided a 50-year net saving of US$25 a square metre. Green roofs were US$96 a sq m more expensive than white roofs and, despite lasting at least twice as long as black or white roofs, could not recover the installation premium. However the report found that despite this, the annualised cost premium of a green roof was just US$3.20 a sq m per year.

This annual difference was small enough that the choice between a white and green roof should be based on preferences of the building owner, for example, whether they valued combating climate change or were concerned with aesthetic values or tackling stormwater management.

The study authors said that the other benefits of green roofs would ideally be included in analysis.

“We’ve recognised the limitations of an analysis that’s only economic,” Mr Mandel said. “We would want to include these other factors in any future study.”

Distinguished Scientist Emeritus Arthur Rosenfeld

Black roofs pose a health risk

The researchers said black roofs posed a major health risk in cities that had high summer temperatures.

“In Chicago’s July 1995 heat wave a major risk factor in mortality was living on the top floor of a building with a black roof,” Dr Rosenfeld said.

With Australia experiencing increasing heat waves, there has been concern over the continued popularity of black tiles on residential properties.

Dark-coloured pavements and roofs were noted as a contributing factor to the urban heat island effect, which the latest State of Australian Cities report predicted would contribute to heatwave-related deaths.

An article published in Renew magazine pointed to three factors that has led to the continued use of black roofs in Australia.

First was the notion that people had an aesthetic preference for black roofs, as they were considered to blend in better.

Second was the building industry, which the article stated did “tend to set trends” based on perceptions of customer desire.

“Builders install them because they think customers want them, and customers want them because ‘the building industry always uses dark roofs, so they must be the best option’,” the article stated.

Another environmentally disastrous product that had persevered thanks to builders was halogen down lights, which were installed because they were cheap to buy and because there was a perception they were more desirable, however running costs were extremely high, a factor that seemingly did not enter the equation.

Finally, the article stated that many local councils had restrictions on how light a roof could be, perhaps because the majority of roofs were dark and a degree of likeness needed to be employed.

Dr Rosenfeld said government should have an active role in limiting the use of black roofs, and supported building code policies that phased out dark-coloured roofs in heat-prone climates.

“White doesn’t win out over black by that much in economic terms, so government has a role to ban or phase out the use of black or dark roofs, at least in warm climates, because they pose a large negative health risk,” he said.

Dr Rosenfeld has been a longtime supporter of solar-reflective “cool” roofs, including white roofs, as a way to reduce energy costs and address global warming. He co-authored a 2009 study in which it was estimated that making roofs and pavements around the world more reflective could offset 44 billion tons of CO2 emissions. A later study using a global land surface model found similar results: cool roofs could offset the emissions of roughly 300 million cars for 20 years.

20 replies on “Study: white roofs reign supreme”

  1. For over a decade, The EPDM Roofing Association (ERA) has been the leading researching body and voice for manufacturers of both white and black EPDM single-ply roofing systems.

    Based on our concern that this study, released by Lawrence Berkeley National Laboratory, is flawed, ERA assembled a team of experts to provide analysis of the study and detail its extreme shortcomings. Their analysis found that the LBL Researchers failed to follow certain scientific processes, and that the report frequently relied on anecdotal data, potentially biased or incomplete interpretations of data, and lacked quantitative sources of data. The complete analysis can be found at https://www.epdmroofs.org.

    Furthermore, ERA rejects the recommendation contained in the study that black roofing be banned in warmer climates. Due to the complexity of roof and building science, prescriptive requirements that limit choices available to the architectural and building owner community are not in the best interest of good roof system design. Our overriding concern is that building owners and their design professionals are provided with science-based, field-tested information to help them make the choice of a roofing system that will meet their needs. Additionally, ERA feels that it is imperative to defer any decision related to roof design to architects and/or roof consultants, who have the proper training and understanding of all of the components found within a roofing system.

  2. For over a decade, The EPDM Roofing Association (ERA) has been the leading researching body and voice for manufacturers of both white and black EPDM single-ply roofing systems.

    Based on our concern that this study, released by Lawrence Berkeley National Laboratory, is flawed, ERA assembled a team of experts to provide analysis of the study and detail its extreme shortcomings. Their analysis found that the LBL Researchers failed to follow certain scientific processes, and that the report frequently relied on anecdotal data, potentially biased or incomplete interpretations of data, and lacked quantitative sources of data. The complete analysis can be found at https://www.epdmroofs.org.

    Furthermore, ERA rejects the recommendation contained in the study that black roofing be banned in warmer climates. Due to the complexity of roof and building science, prescriptive requirements that limit choices available to the architectural and building owner community are not in the best interest of good roof system design. Our overriding concern is that building owners and their design professionals are provided with science-based, field-tested information to help them make the choice of a roofing system that will meet their needs. Additionally, ERA feels that it is imperative to defer any decision related to roof design to architects and/or roof consultants, who have the proper training and understanding of all of the components found within a roofing system.

  3. White roofs are glary. That’s already proscribed in some jurisdictions.
    In Japan, black roofs are exploited to cause ventilation drafts, the hot black surface makes the internal heat rise up.
    In winter this heated air can be recirculated under the floor for home heating.
    In summer this draft can exhaust warm air from within the house.
    Banning dark roofs would be unwise. However if dark roofs were not used as described above or in some other sensible way then they could be proscribed.

  4. White roofs are glary. That’s already proscribed in some jurisdictions.
    In Japan, black roofs are exploited to cause ventilation drafts, the hot black surface makes the internal heat rise up.
    In winter this heated air can be recirculated under the floor for home heating.
    In summer this draft can exhaust warm air from within the house.
    Banning dark roofs would be unwise. However if dark roofs were not used as described above or in some other sensible way then they could be proscribed.

  5. Sorry to be pedantic, but after living in North America for 8 years and hearing far too much about the “Maple LEAFS” hockey team, I would have thought Australia hadn’t taken “leaves” out of North America’s language book – and the word roves would be used instead!

  6. Sorry to be pedantic, but after living in North America for 8 years and hearing far too much about the “Maple LEAFS” hockey team, I would have thought Australia hadn’t taken “leaves” out of North America’s language book – and the word roves would be used instead!

  7. Interesting timing for such an article. With BASIX announcement of an increase to thermal comfort targets. I have seem many assessors solutions to reaching the new very stringent heating caps is to use dark walls and/or a dark roof for a Sydney climate.

    Summer cooling targets are generally very easily achieved but the real challenge is winter heating loads.

    Not a great built outcome but I expect an influx of dark colours in the future for NSW areas with moderate climates.

    1. Well that sounds counter intuitive. Be grateful for further thoughts on this little chestnut! Thought the big issue in Syd was the hot weather…but then hardly anyone owns a jumper… maybe that’s why some people think they need dark roofs.

  8. Interesting timing for such an article. With BASIX announcement of an increase to thermal comfort targets. I have seem many assessors solutions to reaching the new very stringent heating caps is to use dark walls and/or a dark roof for a Sydney climate.

    Summer cooling targets are generally very easily achieved but the real challenge is winter heating loads.

    Not a great built outcome but I expect an influx of dark colours in the future for NSW areas with moderate climates.

    1. Well that sounds counter intuitive. Be grateful for further thoughts on this little chestnut! Thought the big issue in Syd was the hot weather…but then hardly anyone owns a jumper… maybe that’s why some people think they need dark roofs.

  9. Its odd that this piece for an Australian audience does not refer to such studies as the South Australian Governments study on cool roofs for both commercial and residential buildings in 2010 which led to specific requirements for commercial buildings .. and the City of Melbourne Sept 2011 study… the SA government funded study covers BCA climate zones 4,5 and 6. for residential buildings other than in hotter zone 4 (cooling dominated) there is a benefit to a lighter coloured roof, not so for still heating dominated climates 5 & 6 ( this is BCA zone for Melbourne) ..Insulation is of course a big factor in modelling the effect of roof colour effects..

  10. Its odd that this piece for an Australian audience does not refer to such studies as the South Australian Governments study on cool roofs for both commercial and residential buildings in 2010 which led to specific requirements for commercial buildings .. and the City of Melbourne Sept 2011 study… the SA government funded study covers BCA climate zones 4,5 and 6. for residential buildings other than in hotter zone 4 (cooling dominated) there is a benefit to a lighter coloured roof, not so for still heating dominated climates 5 & 6 ( this is BCA zone for Melbourne) ..Insulation is of course a big factor in modelling the effect of roof colour effects..

  11. Good article- thanks.
    I think the phenomenon of whole suburbs of black and very dark grey & dark brown roofs, is largely a result of what project builders offer & what they have in their display homes. They tend to follow one another & offer very similar products. It’s just a fashion. Often to top it off there is a matching black driveway- double of course! Pity any child who walks over this barefoot on a hot day- the heat is remarkable.

  12. Good article- thanks.
    I think the phenomenon of whole suburbs of black and very dark grey & dark brown roofs, is largely a result of what project builders offer & what they have in their display homes. They tend to follow one another & offer very similar products. It’s just a fashion. Often to top it off there is a matching black driveway- double of course! Pity any child who walks over this barefoot on a hot day- the heat is remarkable.

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