Study: Green Roofs Low in NYC


In a recent study, the Nature Conservancy (New York City), The New School (New York City), Columbia University (Palisades, New York) and the Wildlife Conservation Society (Bronx, New York) looked at the number of green roofs within New York City.

According to researchers, in 2016 the city contained more than 1 million buildings. However, only 736 contained green roofs—accounting for less than 0.1% of all buildings.

“If we are going to meet our goals for climate adaptation, sustainability, and equity, we have to invest more in our green roofs alongside other green spaces,” said co-author Timon McPhearson, professor of urban ecology at The New School, in a release.

“The unmet opportunity to transform the flat roof space in New York City is vast. Mobilizing city resources to expand green roofs, especially in underserved neighborhoods, could go a long way towards cooling the city, improving stormwater resiliency, and providing new recreation spaces.”

NY Green Roof History

The New York City council approved a package of bills and resolutions, including Local Laws 92 and 94, in April 2019.

Local Law 92 was originally introduced by Council Member Donovan J. Richards on Jan. 31, 2018, and looks at residential buildings that are five stories or fewer and have less than 100 square feet of rooftop space. In this instance, the building would be required to install a green roof option or solar-electricity-generating system, depending on the structure’s dimensions.

Richards' bill also requires that the Department of Housing Preservations and Development perform a study on the potential impact of green roofs and building affordability.

Local Law 94 was introduced by Council Member Rafael L. Espinal, Jr. on July 7, 2018, and promotes an energy-efficient building practice, which requires that all commercial and manufacturing buildings are required to install an energy-efficient green roof.

“It’s important for New Yorkers to know that green roofs are going to play a major role in making our city a more livable city from lowering the temperatures of our communities to improving air quality across the city,” said Espinal.

“The implementation of Local Laws 92 and 94 of 2019 will ensure that New York City is at the forefront of the transition to a cleaner and greener future for all New Yorkers,” said Richards.

“Utilizing valuable rooftop space to continue reducing our carbon emissions will also help reduce energy costs, improve stormwater management and make our city more livable for generations to come. We look forward to seeing more and more innovative ways to enhance green infrastructure as buildings begin to pop up in compliance with these laws and I’d like to thank Council Member Espinal for his commitment to green energy as well as Mayor de Blasio, Commissioner La Rocca and Director Chambers for their partnership on the Climate Mobilization Act.”

The passing of the green roof legislation came on the heels of former mayor Bill de Blasio’s release of $14 billion act, OneNYC2050—Building a Strong and Fair City. The new legislation will cover new buildings, as well as those undergoing major renovations, and is intended to cut the city’s greenhouse emissions by 30% by 2030.

There are two major parts of the initiative that impact the building and construction industry. Those include:

  • Requiring buildings cut their emissions. With the passage of the building mandates law, New York City is the first city in the world to require all large existing buildings of 25,000 square feet or more, of which there are 50,000 citywide, to make efficiency upgrades that lower their energy usage and emissions or face steep penalties, according to the report.
  • Banning new inefficient glass-walled buildings. The city will no longer allow all-glass facades in new construction unless they meet strict performance guidelines, making inefficient glass-heavy building designs a thing of the past.

In the requirements of the new bill package, the green roofs are slated to help mediate the urban heat island effect, aid in cutting energy costs, help absorb air pollution, reduce stormwater runoff, provide soundproofing and promote biodiversity.

“The implementation of the law expanding green roofs is a win for our environment, our economy and our communities,” said Espinal.

“At a time when national policy seems to turn its back on our planet, it is up to cities like New York to lead the fight against climate change. To do that, we have to adopt policies that take advantage of our unique, untapped assets. I am proud to have been a part of a team of activists and communities who are working to change this concrete jungle into a green oasis.”

By November, the new green roof laws were reported to be in full effect.

Local Law 92 and Local Law 94 require that all new buildings and all existing buildings undergoing major roof renovations to have a solar photovoltaic system, a green roof system or a combination of the two. The systems must cover 100% of any applicable roof.

Per the regulations, all new application filings for new building projects and alteration projects that include vertical and horizontal enlargement or replacement of the entire roof deck, were required to include a form certifying their compliance with Local Laws 92 and 94 prior to plan approval from the Department.

Study Findings

Since published in the journal Ecology and Society, the study is reported to be the first publicly available citywide dataset of green roof distribution throughout New York City. While previous research has aimed to quantify green roof coverage in the area, the team instead turned to the state’s database of publicly available satellite imagery.

Covering virtually all parts of the city in resolutions as high as six inches, researchers were able to identify images depicting a birds-eye-view of 155 buildings clearly featuring green roofs. From this sample, they then trained a machine-learning model to comb through the millions of other overhead shots of rooftops in New York City.

“Companies and building owners have installed green roofs in an effort to retain stormwater, but there is no central registry of these installations,” study co-author Greg Yetman from the Columbia University Climate School said in a release. “Detecting the roofs from imagery was an ideal way to locate both large and small installations without having to survey building owners.”

While it is likely that the analysis missed some green roofs existing in 2016 and was unable to account for the fluctuation in the number of green roofs since the images were gathered, researchers were able to confidently share that the green roofs occupied roughly 62 acres citywide.

Unevenly distributed, more than 50% of the roofs were concentrated in Manhattan. However, on a citywide scale, neighborhoods most vulnerable to urban heat-island effects were reported to be underserved by green roofs. According to research findings, 22 of the neighborhoods observed contained less than 10 green roofs, while four contained zero.

With this new data in mind, the study authors say that governments and nonprofit groups will be better guided to plan more effective initiatives to implement more green roofs in New York City.

“This information, as well as insights on the types of buildings we see green roofs on … is ultimately invaluable in working with policymakers, advocates, and researchers to expand green roofs, particularly in areas where they are most needed,” Treglia said in a release.

A full copy of the study can be read here.

Green Roofs Elsewhere

Since New York’s implementation of green roof legislation, several other U.S. cities have followed suit. Shortly after going into effect in the state, St. Louis became the latest city to pass green roof legislation—in this case, roofs on new construction must be “solar ready.”

Board Bill 146, which was signed into legislation in December by former mayor Lyda Krewson and was unanimously approved by the city’s Board of Aldermen, applies to commercial, residential and multifamily construction. Lawmakers cited energy savings for the push.

The requirement is also in compliance with the 2018 International Energy Conservation Code and goes toward the Michael Bloomberg initiative (which the city is a member of) to fight climate change.

In March 2021, a proposed bill in Massachusetts was looking to make the state the latest in to require solar roofs on new residential and commercial buildings. The Solar Neighborhoods Act was reportedly filed at the beginning of the month, with a companion bill filed in the Senate.

Bill mandates include:

  • All new buildings will be built “solar-ready,” or able to accommodate rooftop solar panels. The Department of Energy Resources will develop amendments to the state building code ensuring that roofs are strong enough to support solar panels, available roof space is maximized and buildings can accommodate the necessary electrical infrastructure;
  • Rooftop solar panels must be installed on new buildings at the time of construction, including single-family homes, apartment buildings and commercial buildings;
  • For single-family homes, the solar energy system must produce enough electricity on an annual basis to meet 80% of the average demand for similar houses;
  • For other buildings, DOER will establish minimum requirements for the size of solar energy systems; and
  • Buildings may be exempted from solar roof requirements if the roof is too shaded, if a solar hot water system or other renewable energy technology is installed or if the building has a green roof. DOER can also grant exemptions to affordable housing developments.

In the last session, the Joint Committee on Telecommunications, Utilities, and Energy was favorable to the legislation but has yet to advance it to a vote on the floor of either chamber.

Most recently, in France the Senate approved new legislation requiring that the roofs of existing and new car parks with at least 80 spaces be covered by solar panels.

Noted to be part of President Emmanuel Macron’s renewable energy plan, the bill mandates the solar canopies to be in place within the next five years.

According to reports, when the bill was first introduced it required that car parks measuring more than 2,500 square meters (nearly 26,910 square feet) would have to cover at least half of the park with solar panel canopies. This detail was later refined to the number of spaces.

Per the final document approval, which took place on Nov. 4, car parks with more than 400 spaces must be brought into compliance within three years. For car parks with 80-400 spaces, owners will have five years to comply. At least half of the car park surface must be covered by solar panel canopies or another renewable energy source.

Several amendments were also made regarding the new legislation and have since been supported by the French government. Of them, Nathalie Delattre (RDSE) and the centrist Stéphane Demilly had parking lots for heavy goods vehicles (over 7.5 tons) explicitly excluded. The legislation is also invalid for parking areas near remarkable sites—whether they are classified as protected areas or not—to avoid “distorting” them.

The possibility of granting additional time to parking managers in the event of being unable to acquire solar panels, however, has been denied.

For managers who are not compliant with the next legislation by the allotted timeframe will be forced to pay monthly sanctions based on the number of equipped places, in this case, 50 euros ($51.38) per place. As an example, a car park with 80 spaces that fail to comply with the new legislation would be exposed to 48,000 euros in penalties each year.

Provisions outlined in the legislation will come into force on July 1, 2023.


Tagged categories: Building codes; Colleges and Universities; Color + Design; Design - Commercial; Government; Green Infrastructure; Green roofs; NA; North America; Projects - Commercial; Regulations; Research; Research and development; Solar

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