Many cities are repurposing their roofs, turning underutilized areas into beneficial spaces. Green roofs involve planting vegetation on roofs, thus providing energy savings for building owners and larger effects for the wider city area. Cities benefit from a reduction of the heat island effect, a situation where mass-urbanization causes higher temperatures around city centers. Since they trap rainwater and slow runoff, green roofs also improve drainage and offer better sanitation to cities where sewage systems overflow from heavy storms.
Early Green Roofs
Some of the first green roofs can be traced back to early Scandinavian history where Vikings used their local resources to adjust to harsh climate conditions. By lining their longhouses with local materials such as birchwood and sod, they were able to create sturdy, insulated structures for the cold winter.  This later developed into the well-known Scandinavian sod roof houses which used a base of stone covered by sod. The designers artfully integrated the natural landscape with the design of these homes. By offering superior insulation compared to just wood or stone, the use of local materials proved to be resourceful and effective. These types of sod roof houses were used up to the late 1800s.
Modern Green Roofs
The reemergence of green roofs had a slow start in mid-twentieth century Germany. Rooftop vegetation was originally installed to mitigate the effects of solar radiation and for fire retardation.
These green roofs were similar in design to the earlier rough green roofs in Scandinavia but became more strictly defined, composing of a waterproof membrane, a drainage layer, a growing medium, and plants.  Progress in environmental thought, policy, and technology occurred in Germany as a result of growing environmental concerns in urban areas.  This led to research in green infrastructure and low-impact development such as green roofing and the design of permeable pavements. The new advances in research led to green roofs that were easier to maintain and understand. Green roof technology became widely accepted by the public because of its environmental benefits and the nature of interdisciplinary research that Germany had taken the lead in. Environmental technology was supported through the use of incentives and requirements at multiple levels of government. Policies included federal nature-protection laws and building codes to mitigate stormwater runoff due to manmade impermeable surfaces and greenfield development. In German states, these began with incentive programs but later turned to requirements for the implementation and maintenance of green infrastructure. In the 1970s, a series of federal and state court rulings made stormwater services transparent leading to service rates dependent on the stormwater burden generated by a property known as individual parcel assessments (IPAs). By basing fees for the stormwater services on IPAs, land-use decisions became more focused on environmentally conscious techniques such as green roofs and other semi-permeable surfaces to minimize these costs. This provided incorporation of an economic factor to green technology implementation.
Accreditations and Accreditors
Certain credentials have arisen in the United States to ensure there are professionals who understand structural and safety considerations in implementing a green roof. The most general credentials are particular to a profession such as Professional Engineer (PE) or Registered Architect. However, more specific credentials have arisen for green roof technology, namely the Green Roof Professional (GRP) accreditation by Green Roofs for Healthy Cities (GRHC) which is the leading accreditation in North America for predesign, design, contract management, quality assurance and support, and maintenance. The licensure ensures that professions understand the design issues unique to green roofs. By creating certification programs for providers of these relatively new technologies, a degree of organization and accountability is put into place. This aids the client in deciding who to employ and aids the service provider in obtaining clientele trust. These credentials help bring validity to a service provider while assuring quality which prevents less-knowledgeable imitators.
Standards and Rating Systems
Standards and green building rating systems arose with the rise of green building technology. Standards involve defining building quality beyond code levels that lead to performance improvements.The American Society of Heating, Refrigerating and Air-Conditioning Engineerings (ASHRAE) makes many building performance standards. Despite the inability to enforce them, many municipalities willingly adopt these as the basis of their code thus gaining legal backing. In addition, many organizations have established themselves in defining high-performance and green certifications. These include LEED, Energy Star, Green Globes, Living Building Challenge and many others that play a role in enticing investors and improving public image; a sort of social corporate responsibility.
Concern over Building Integrity
With uncommon green roof collapses such as a 2013 supermarket collapse in Latvia and a 2011 collapse in Illinois, people question whether the added weight of green roofs adversely impacts the structural integrity of the building. Since green roofs retain more storm water than traditional roofs, people also want to be sure that their roofs are watertight, unlike the roof of the New York Barclays Center, which interrupted a basketball game because of a leak.
Expense of Green Roofs
There are questions over whether the benefits green roofs offer warrant their higher cost. A worker at the Javits Center in New York City expresses concern over justness of using tax payer money for a green roof costing in excess of $200 million, resulting in a roof that still leaks. Furthermore, some people debate the direct financial benefits offered to building owners: Ecology Professor Matt Palmer states that "some of the benefits of green roofs can be realized at lower cost with other technologies," citing that energy benefits "can be achieved more cheaply through better insulation and HVAC upgrades." 
Technologies that directly impact people other than the buyer and seller are said to have externalities, and can either benefit others (a positive externality) or cause unwanted side-effects (negative externalities). With positive externalities, the true benefit of the technology is greater than what is paid by the purchaser. Consequently, societal demand is greater than the demand of those who have purchasing power; the amount of technology produced falls short of the socially optimal amount.
Green roofs are one such technology that offers positive externalities in cities. While a building owner has some financial incentives to build a green roof, citizens will benefit when a city converts a critical mass of rooftops. Reductions in stormwater runoff and the heat island effect are felt only when a significant portion of the city has green roofs.
To help attain a socially optimal amount of green roofs, governments and private organizations provide subsidies. The city of New York provides a tax abatement of $4.50 per square foot of green roof "to prevent the City's sewer system from overflowing into rivers," also citing numerous other benefits. The Anacostia Watershed Society offers similar subsidies in the Washington D.C. area, with other financial incentives nationwide. By providing subsidies, costs of publicly beneficial technologies shift to the people who benefit from them.
Green Roofs as Restorative Environments
Restorative environments are natural environments that restore degraded mental processes in humans. Due to the stress of urban stimuli, city life can often demand the use of mental functions that lead to fatigue. The mental process of attention often suffers the most, especially in the workplace where additional stressors are introduced. Rachel Kaplan theorized that directed, focused attention needed to perform tasks in the workplace must be aided by fascination, a form of effortless attention evoked by restorative environments as simple as windowed work areas and short exposures to nature.
Green roofs show potential to serve as restorative environments. Walkable green roofs are common and provide a small nature experience during a short break. Views of green roofs even without physical access could contribute significantly to job satisfaction, as Kaplan observed. Green roofs also help reduce unwanted stimuli from the city by absorbing sound waves.
Passive technologies can be defined as technologies that do not require significant user input to perform some function. Green roofs, particularly extensive green roofs with a growth medium of six inches or less, can be considered passive technologies since they are low-maintenance yet still perform their function by offering a number of benefits to the urban environment.
Passive technologies convey an important lesson at the social interface. Participants often have shared values and goals, but many are not willing to become involved in influencing change because doing so would demand some alteration of their lifestyle. Some cultures do demonstrate the capacity to reach their goals through cooperative lifestyle changes, as in the case of Japan's Cool Biz campaign, but in many others people need the assurance that their lifestyles will not be altered for some higher cause. The beauty of passive technologies is that they perform a desired function that would otherwise demand some unwanted user input.
Other examples of passive technologies include smart thermostats and fluoride. These technologies are still subject to the same level of scrutiny in the eyes of the public as any technology at the social interface.
Building Consumer Trust
Consumer trust in green roof companies is key to the social acceptance and implementation of the technology. Recall the participants concerned about green roofs posing structural and waterproofing issues. To mitigate this mistrust in the technology, some companies write blog posts to assure consumers that the technology is safe: Urbanscape claims their lightweight system is "six times lighter than traditional ‘intensive’ green roof system," eliminating the need for "prohibitively expensive" structural reinforcement. While this sponsored content raises questions of bias, their logic seems sound in this case, and they succeed in using professionalism to convey safety. Furthermore, contractors can earn the "Green Roof Professional" accreditation offered by the non-profit Green Roofs for Healthy Cities (GRHC). GRHC gives this accolade so professionals can display it to consumers and "increase customer confidence in green roof technology" through "better green roof design and installation practices." This accolade builds on top of permit processes and inspections that cities like Chicago and New York require of green roof projects. Because of consumer concerns, organizations responded by enacting measures to verify engineering procedures.
Although certifications and permits are impediments that increase the cost of projects, they give consumers much-needed assurance that their lives are in good hands. Consumers often do not have the time or expertise to individually verify engineering practices, so they must rely on third parties for confidence.
Green roofs will continue to be shaped by the values of the people that interact with them and will require acceptance to truly be effective at the social interface. Green roofing is not an issue with diametrically opposed groups; rather, it is an issue of policy-making influenced by different participant groups and continued research on its pros and cons that either allows or inhibits the technology. Small progressive stages of policy implementation as well as incentives work to shift preference towards green roofs from their counterparts. Viewing the technology through the lens of the social sciences can help people understand the alignment of their values and the values embedded in green roofing.
Future work on this topic should study the cultural differences and policy differences that might allow green roofing to be more successful in Germany than in the United States. Another interesting contribution could be predicting future participant groups that would form if green roofs started becoming more mainstream.
- Zachary Small. (n.d.). The green roof: how ancient architecture shaped modern sustainable design. www.hopesandfears.com 
- Köhler, M., Schmidt, M., Grimme, F., Laar, M., Tavares, S., & Paiva, V. (2002). Green roofs in temperate climates and in the hot-humid tropics - far beyond the aesthetics. Environmental Management and Health, 13(4), 382–391. http://doi.org/10.1108/09566160210439297
- David A. Williams. (2009). Appropriate design elements and soil selection for green roofs in North Central Texas. ProQuest LLC.
- Oberndorfer, E., Lundholm, J., Bass, B., Coffman, R., Doshi, H., Dunnett, N., … Rowe, B. (2007). Green roofs as urban ecosystems: ecological structures, functions, and services. BioScience, 57(10), 823–833.
- Buehler, R., Jungjohann, A., Keeley, M., & Mehling, M. (2011). How Germany became Europe’s green leader: a look at four decades of sustainable policymaking. Solutions, 2(5).
- Urban Green Council. (2014). GPRO: Fundamentals of building green. U.S. Green Building Council New York
- Latvia supermarket roof collapse kills dozens. (2013, November 22). Retrieved December 13, 2015, from http://www.abc.net.au/
- Walberg, M. (2011, February 14). Grass-covered 'green roof' collapses in St. Charles. Retrieved December 12, 2015, from http://articles.chicagotribune.com/2011-02-14/news/ct-met-aquascape-roof-collapse-20110214_1_green-roof-collapse-aquascape
- Abramson, M. (2014, December 17). Leak in Barclays roof delays game as Nets' comeback fall short vs. Heat. Retrieved December 13, 2015, from http://www.nydailynews.com/sports/basketball/nets/leak-barclays-center-roof-delays-nets-heat-game-article-1.2047824
- Buiso, G. (2014, January 26). Javits Center roof continues to leak despite $465M fix. Retrieved December 13, 2015, from http://nypost.com/
- Palmer, M. (n.d.). Why don’t all public buildings have green roofs? Retrieved December 13, 2015, from http://www.thenatureofcities.com/2015/08/12/why-dont-all-public-buildings-have-green-roofs-or-all-large-private-buildings-e-g-businesses-would-this-be-a-good-idea-what-would-it-take-to-make-it-happen-and-to-make-it-worthwhile/
- Colander, D. C. (2013). Market Failure versus Government Failure. In Microeconomics (9th ed., pp. 164-167). New York, NY: McGraw-Hill.
- New York City Mayor's Office of Sustainability. (n.d.). Green Roof Tax Abatement. Retrieved December 12, 2015, from http://www.nyc.gov/html/gbee/html/home/home.shtml
- Anacostia Watershed Society. (n.d.). RiverSmart rooftops. Retrieved December 12, 2015, from http://www.anacostiaws.org/
- Staats H. (2012). Restorative environments, in The Oxford Handbook of Environmental and Conservation Psychology, ed Clayton S., editor. (New York, NY: Oxford University Press; ), 445–458. http://www.oxfordhandbooks.com/view/10.1093/oxfordhb/9780199733026.001.0001/oxfordhb-9780199733026-e-24
- Kaplan, R. (1993). The role of nature in the context of the workplace. Landscape and Urban Planning, 26, 193-201. http://deepblue.lib.umich.edu/bitstream/handle/2027.42/30542/0000175.pdf?sequence=1
- Getter, K.L. & Rowe, D.B. (2006). The Role of Extensive Green Roofs in Sustainable Development. HortScience, 41(5), 1276-1285. https://www.msu.edu/course/atm/431/LowImpact/Getter%20HS%20Review%20Aug%2006.pdf
- Passive/active tech. http://www.sccs.swarthmore.edu/users/97/jahall/thesis/tech/actpassive.html
- Extensive green roofs. http://www.greenrooftechnology.com/extensive-green-roof
- Tomazin, M. (2015, November 27). How much does a green roof weigh? Retrieved December 13, 2015, from http://blog.green-urbanscape.com/blog/
- Green Roofs for Healthy Cities. (n.d.). GRP accreditation. Retrieved December 13, 2015, from http://www.greenroofs.org/
- City of Chicago. (n.d.). Green permits. Retrieved December 12, 2015, from http://www.cityofchicago.org/
- New York City Department of Buildings. (n.d.). Green roofs. Retrieved December 12, 2015, from http://www.nyc.gov/html/dob/html/sustainability/green_roofs.shtml