How to decide between a white or green roof

Black roofs are out, and white and green roofs are in. But which environmentally-friendly option gives you the most bang for your buck?

Roofing has become an environmental and public health issue in cities because commonly-used dark roofs absorb sunlight, heating the building and driving up air-conditioning use and heat-related deaths. In contrast, white roofs reflect sunlight, and green roofs covered with plants insulate the building from heat.

The authors of a new report in Energy and Buildings set out to tally the economic advantages and disadvantages of white and green roofs. First, they note that green roofs don’t reflect sunlight as well as white roofs. White roofs are about three times better at cooling the planet than green roofs, the team estimates.

The researchers then studied the costs involved in installing, maintaining, and replacing each type of roof over 50 years. They also accounted for benefits such as the money saved from lowering AC use, reduced greenhouse gas emissions from power plants, global cooling, and improving stormwater management.

Green roofs cost more to install, and they require owners to tend to the plants, particularly as the gardens are first becoming established. On the other hand, white roofs actually perform worse on energy savings because although they’re good at cooling buildings in the summer, they can drive up heating bills in the winter.

Overall, green roofs cost about $96 per square meter more than white roofs over 50 years, the team concludes. However, the cost difference per year is “sufficiently small that the choice between a white and green roof should be based on preferences of the building owner,” the authors write. The analysis didn’t account for other benefits of green roofs, such as offering natural habitat patches. “Owners concerned with global warming should choose white roofs,” they advise, while those “concerned with local environmental benefits should choose green roofs”. Roberta Kwok | 28 January 2014

Source: Sproul, J. et al. 2014. Economic comparison of white, green, and black flat roofs in the United States. Energy and Buildings doi: 10.1016/j.enbuild.2013.11.058.

Image © seeyou | Shutterstock

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2 Comments

  • Jason Aloisio January 29, 2014 at 7:23 am

    Vegetated green infrastructure, in addition to cooling benefits, provide storm-water capture benefits that must be calculated as well. For example, in NYC, PlaNYC suggested that a green infrastructure plan (rich with planted material) could save of about $1.3 Billion in stormwater infrastructure improvement to meet current and projected demand. Moreover, their are positive ties between viewing vegetated landscapes and human health.

    Would you rather be sitting in your office or apartment and look out the window to be blinded by a sea of white and light be reflected into your eyes, or would you prefer a calming view of rooftop meadows, and ivy covered walls. According to White et al., the latter.

    When you take into account the workforce productivity increases, improvements of health and stormwater benefits of green roofs, I think that you gain greater insight into the green vs white roof question.

    Literature Cited:
    PlaNYC Green Infrastructure:
    http://www.nyc.gov/html/dep/html/stormwater/nyc_green_infrastructure_plan.shtml

    Health benefits of nature:
    Ulrich, R. S. 1986. Human responses to vegetation and landscapes. Landscape and Urban Planning 13:29-44.

    Green roof human benefits:
    White, E. V. and B. Gatersleben. 2011. Greenery on residential buildings: Does it affect preferences and perceptions of beauty? Journal of Environmental Psychology 31:89-98.

    Reply

  • EPDM Roofing Association February 20, 2014 at 12:47 pm

    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 http://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.

    Reply

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