In New York City, heavy rains overwhelm the combined sewer system, leading to the discharge of about 27 billion gallons of untreated sewage, including human waste and pollutants, into the city’s waters annually. Each year, about 57 million illnesses in the U.S. are caused by swimming in contaminated oceans, lakes, rivers, and ponds.
Water recreators face higher incidences of gastrointestinal, respiratory, ear, eye, and skin illnesses. The CDC reported that from 2000 to 2014, 140 untreated recreational water-associated outbreaks were voluntarily reported to the CDC, which they had resulted in at least 4,958 cases of disease and two deaths across 35 states and Guam. Among the outbreaks, many were linked to pathogens such as norovirus and E. coli. The economic impact is substantial, with water recreation-related illnesses costing an estimated $2.2-$3.7 billion annually in the U.S., according to a study.
Green roofs, vegetated roofs, made up of multiple layers installed on top of a roof, offer a promising solution to NYC’s water contamination problem. By absorbing and slowing stormwater runoff, green roofs give sewage treatment plants more time to process water before it reaches rivers, mitigating the adverse effects of combined sewage overflow. Studies show green roofs can reduce building runoff by as much as 79% annually. Despite these well-documented benefits, New York City has been slow to adopt green roofs. Out of one million buildings, only 736 have them, accounting for less than 0.1%, according to a study.
But this essential infrastructure is needed more than ever, offering a solution to this growing crisis. As climate change intensifies, with more severe weather and frequent downpours, New York City’s waterways are increasingly at risk. By the end of the century, New York City is projected to experience a 30% increase in annual rainfall due to climate change, amplifying flood risks, according to a report by the Mayor’s Office of Climate and Environmental Justice and the New York City Panel on Climate Change.
In the face of this growing crisis, we must tackle the problems that are stopping the city from expanding green roofs.
Late-adoption
In the U.S., nature-based solutions to manage stormwater were not always accepted. Decision-makers only considered civil engineering solutions to improve water quality. Building gigantic tanks to store rainwater for stormy days was one of the best-fitted solutions considered at the time. But this turned out to be an unfeasible idea: the tanks needed to be huge and sited in places in the city where space was extremely limited.
On the other hand, in Germany when the oil crisis was at its height in the 1970s, the government initiated the exploration of green roofs as a way to conserve energy. By 1989, approximately one million square meters of green roofs had been planted in Germany. Now, the total estimated amount of green roof area in Germany is around 120 million square meters.
The first step to catch up with the late adoption of green roofs is recognizing the benefits of green roofs and nature-based solutions to a wider public. Civil engineering solutions only solve one solution at a time, such as the tank only storing water. But nature-based solutions like green roofs often have versatile benefits from reducing energy usage to creating better habitats to improving water and air quality, which contribute to solving our intensifying issue, global warming. These are the things more people need to recognize, creating a climate for architects, designers, engineers, policymakers, and property owners to actively incorporate green roofs into their designs and decision-making processes.
Research
Due to its slow start, knowledge of this infrastructure in the U.S. is also incomparable to Germany’s. There have been over 30 years of green roof research accumulated in Europe, making guidelines that help with the planning and installation of green roofs. The guidelines are called FLL, which started their development in 1975 and was published in Germany in 1982 and in English in 2002. Since then, FLL has been widely used worldwide, including in the U.S.
But it is necessary to have guidelines tailored to local practices and climates to further expand green roofs. In areas like plant selection, growth media, and drainage, they particularly need to be adapted to the specific conditions of different ecoregions in North America. We cannot solely rely on others’ research; instead, we must conduct our own studies tailored to local conditions to successfully expand green roofs in the U.S.
Financial Incentives
Only four buildings have received the NYC green roof tax abatement, according to a response from the NYC Department of Finance in May 2024 following a Freedom of Information Law (FOIL) request made by Urbanstrong in 2023. Two of the buildings were in Brooklyn, one in the Bronx, and one in Staten Island. The abatement for these four buildings averaged around $11,000 each.
In 2008, the NYC green roof tax abatement began. The tax abatement provided $4.50 per square foot up to $100,000 per building or less depending on tax liability. In 2013, the amount and cap were both increased to $5.23 and $200,000 respectively. Priority community districts, meaning those particularly vulnerable to high levels of heat stress and air pollution, became eligible to receive a $15 tax abatement per square foot from July 19, 2019, to June 30, 2024. In June 2024, the abatement cap was increased from $5.23 to $10 per square and the tax abatement amount for priority community districts remained unchanged.
On the other hand, the Courtyard Greening Program in Berlin from 1983 to 1996, one of the older subsidies that supported the greening of roofs and walls, provided 19.10 euros including construction and design. With strong financial incentives, it successfully greened around 54 hectares of courtyard and roofs during the period.
While NYC’s tax abatement offers a financial incentive and the recent abatement amount increase is significant, the high costs of green roof installations and logistical challenges make it difficult for property owners to adopt these sustainable practices.
Green roofs typically cost around $26 per square foot to install an extensive green roof with shallow layers of substrate, and $100 per square foot for intensive green roofs with deeper layers of substrate.
But in New York, those prices are significantly higher. It usually costs at least $30 to $50 per square foot to install a green roof according to local architects. The obstacles to green roof installation in a place like New York City are significant as it is also laborious. Many streets are quite narrow, meaning it’s hard to get construction equipment onto them. Some buildings are so tall that cranes can’t reach the rooftop, making it extremely difficult to make modifications. On top of that, many parts of the city are historically landmarked, meaning that there are various rules and restrictions on what can be done to buildings.
Without enough budget, people will have to carry the materials themselves. From the truck to the elevator to the rooftops, the carrying of up to over a ton of materials needs to be done by people. We are requiring more incentives and economic support for property owners to install green roofs in the wake of climate change.
New York is making progress by increasing the tax abatement cap and passing Local Law 92 and Local 94 in 2019, which mandate that all new buildings and existing buildings undergoing major roof alterations must have either a solar panel, a green roof, or both. But, these changes need to accelerate, as climate change is rapidly catching up with us.
The negative impacts we’re seeing from water contamination are only the beginning.
During my time interviewing designers, architects, and policymakers involved in working with green roofs, they expressed their urgency about the issue. Despite the challenges of expanding green roofs in New York’s concrete jungle, they work with the hope that the city will one day resemble Germany—though this will likely take decades.
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