Green Roofs In NYC

Problem

The general consensus of urban planners in the 21st century is to make cities more sustainable and more livable. This concept has been influenced heavily by the ideas of Jane Jacobs, the ongoing environmental movement, along with improvements in technology. Jane Jacobs was a community activist that went against the large scale development and transportation projects that Robert Moses helped to pioneer from the 1920’s till the early 1960’s. Jane Jacobs had many ideas about urban planning, but the idea that is most pertinent to this paper is that that neighborhoods should be more liveable. One of her simple, but important rules was that neighborhoods should not be cut off or displaced by large construction projects.^[1],^[2] Major infrastructure projects have occurred far less often since the time of Jane Jacobs. One of the main reasons  for the decrease in major infrastructure projects is because her ideas have become ingrained in the fabric of city planning, especially on the local or community level of the planning process. Other reasons include the implementation of stricter regulations on projects, when pursuing large scale infrastructure projects.^[3] The environmental movement has ushered in a new era of urban planning. Almost all major development projects and infrastructure improvements attempt to leave a smaller environmental footprint than their predecessors. A reasonable amount of major infrastructure improvements are geared towards creating a greener and more sustainable city. This includes everything from wind farms to new trains and bus routes that would lessen the use of automobiles. Another up and coming green technology is the green roof, which lessen stormwater runoff.

The two primary problems that are caused by stormwater runoff are flooding and combined sewage overflows (CSO’s). A secondary concern is the pollution that is contained within stormwater runoff, which is when pollutants that are left on the ground in between rainfall are picked up by stormwater and carried to sewers which then eject the pollutants into NYC’s waterways. What is even worse than the pollution contained by stormwater runoff is the pollution caused by CSO’s. CSO’s are a fancy term, but they are simple to understand. When rainfall enters the sewers of NYC it usually enters the combined sewage system. A combined sewage system is a sewer system that is serves two purposes. Its main purpose is to transport wastewater from residential, commercial and industrial uses to treatment plants which then clean the waste water and dump it into the cities waterways. The second purpose of a combined sewage system is to collect and treat stormwater runoff in the sewage treatment plants and then dump it in our waterways. When there is excess rain the combined sewage system sometimes reaches its holding capacity and has to eject the combined runoff and waste water into the cities waterways before it can be treated by the city’s sewage plants. This leads to the dumping of toxic wastewater into NYC’s waterways.^[6] Most of the city’s sewers are part of an interconnected combined sewer system that makes up about 70% of the cities sewers.^[7] Some NYC neighborhoods are serviced by separated sewer systems where wastewater is carried to wastewater treatment plants and stormwater is collected in a different sewer system and ejected into local waterways. Most of the combined sewage system is placed in older areas of NYC. One big exception is a large section of Staten Island, which is not serviced by either separate sewer systems or combined sewage systems. This section of the island is serviced by the Staten Island bluebelt, a wetland system that conveys, stores and filters stormwater, saving tens of millions of dollars on traditional sewer systems. This is a great example of how the government can use natures own stormwater filtration capabilities as a tool for water management.

NYC does not meet the federal mandates that require a city’s CSO capture rate to be at a certain minimum. Even though this is the case, NYC has come a long way. “NYC’s existing infrastructure developments have increased DEP’s standardized CSO capture rate from about 30% in 1980 to over 72% today.”^[8] They city is required to increase capture rate to 75%, which is lower than the 85% capture rate required by federal law.^[9] NYC has approximately, “7,400 miles of sewer pipes; 135,000 sewer catch basins; over 495 permitted outfalls for the discharge of combined sewer overflows (CSOs); 95 wastewater pumping stations that transport water to 14 wastewater treatment plants located throughout the five boroughs.”^[10] This vast infrastructure is expensive to keep track of and maintain, let alone add to, but NYC is slowly solving its sewage problems. What is shocking though is that there are 495 sites where sewage is discharged in NYC. About, “27 billion gallons of raw sewage and polluted storm water are discharged into the harbor,” every year and as little as “a tenth of an inch of rain coming very quickly can overload that system.”^[11] This is reason to be concerned, since NYC does receive plenty of rainfall every year.

The NYS Department of Environmental Conservation lists the six ways that urban planners can mitigate CSO’s from occurring. They include separation of stormwater and sewer lines, storage tanks to hold overflow during storm event, expansion of waste treatment capacity, retention basins to hold overflow during storm events, screening and disinfection facilities for the overflow, and green infrastructure to reduce stormwater flows into the combined sewer system.^[12] The separation of stormwater and sewer lines would require large amounts of construction, temporary loss of drainage and cost billions of dollars. New storage tanks, the expansion of waste treatment capacity would require some construction and become an eyesore on the community they are placed in. Retention basins are better, but would take up large amounts of valuable land that could be developed on. Screening and disinfection facilities are good, but expensive. On the other hand, green infrastructure requires less invasive construction and uses the natural environment as a way to reduce stormwater runoff and CSO’s.

NYC is one of the most impermeable cities in the country; there is a reason why they call it the concrete jungle. Approximately 220 square miles of the city’s 350 square mile land mass is impervious to water. This means that impervious surfaces cover approximately 72% of a city already surrounded by water.^[13] The age, vastness and inaccessibility of the sewer system means that upgrading the entire sewage system would be a herculean feet.

The density of the city does not lend itself to large swaths of grass or other vegetative areas. New York does have some big parks, but one only has to look at lower Manhattan to see where the problem lies. A more permeable city would be a good thing because it would allow for the absorption of more stormwater. For example, “From 1984 to 2002, 9,000 acres of trees, bushes and vegetative cover were paved over. That land, according to government analysts, could have absorbed 243 million gallons of water for each inch of rain that fell on the city.”^[14] In order to make up for the lost water absorption, the city has already built 2 massive holding tanks and is in the process of building another 2. These projects are expensive and take up space, and they are not as sustainable as building vegetative areas. It is the hard and expensive solution to one that could be done using green infrastructure, which will be discussed further in the solutions section of this paper.

CSO’s are not the only problem caused by stormwater runoff. Chemicals, nutrients, sediment and other pollutants and debris that is on the city streets and rooftops is collected by the stormwater runoff and transported into our waterways. Of course, the biggest concern when it comes to pollution in  regards to water management is the CSO’s but the pollution in stormwater runoff, “In addition to being cited as a major source in one-third of all impaired waters, urban/stormwater runoff is noted as a major source of contaminants in 36% of all waters that experience lesser, but measurable, minor impacts to water quality, and a contributing source in nearly half (47%) of waters with minor impacts,”^[15] The pollution caused by stormwater runoff alone combined with the pollution caused by CSO’s puts our waterways in jeopardy. But, there is a lot of hope. In fact, many waterways in NYC have become less polluted thanks to the large amounts of regulations and laws put into effect starting with the Clean Water Act, which was passed in 1972.

The Clean Water Act of 1972, passed by the United States Congress and signed into law by the  President. The act was the beginning of federal regulations regarding water management. The law was an attempt by the federal government to protect that water of the United States and to try and clean up any damage that was already done. Since the act point sources of pollution are no longer allowed to discharge pollutants into surface waters, without a permit. Point sources include industrial facilities, municipal governments and some agricultural facilities. CSO’s are a kind of point source pollution.^[16]

There are other problems that must be addressed before the solution is to be discussed. One of these problems is rising energy costs and consumption in NYC. Even though NYC uses less energy per capita than other cities across the nation. In fact the average New Yorker uses about one-third the energy of the average American.^[17] NYC is trending towards spending more on electricity and heating costs in the future, but less per capita. Natural gas costs fluctuate over time, but are continuing to steadily rise as fuel becomes more scarce.^[18] Still there is more that can be done to lessen energy costs throughout NYC. One solution that could help mitigate energy costs are green infrastructure, which will be discussed further in the solutions section of this paper.

Solution

Green infrastructure includes more natural solutions such as swales, green roofs and tree planting. “Basil B. Seggos, chief investigator at the Hudson River Riverkeeper, an environmental organization, wants the city to take a less intrusive approach that could actually reduce the amount of runoff that ends up in the combined sewers.”^[19] Mr. Seggos made a push for green roofs to be incorporated into the cities plan. Green roofs seem to be able to mitigate many environmental problems that were discussed in the problem section of this paper. They are also in line with the ideas of modern non-intrusive urban planning that Jane Jacobs pioneered. They are simple solution to a large swath of problems and even have a few unexpected benefits. The main focus of this paper is to cover the implementation of a plan to increase the amount of green roofs used in the city.

This plan will explain how a new nonprofit dedicated to installing cheaper high quality green roofs is a good idea and will help to spur developers, business owners and landlords to build green roofs. This could be done through a public campaign, developing a central location and website where all the current information on green roofs could be accessed. A further step could be lobbying the government to incentivize green roofs even more. The heart of the movement though would be going to building owners and attempting to persuade them to install green roofs by explaining to them the environmental, economic and financial benefits of green roofs. This could be done by attempting to find an incubator space. Eventually, if the nonprofit can raise money it might be able to attract certified engineers, horticulturists, architects and landscape architects to design and install cheaper more affordable green roofs than are currently offered by companies within NYC. There are many impediments to this process, including the cost of greenroofs, the regulations involved in getting one certified and the other competing green infrastructure alternatives, which are often cheaper and more effective than green roofs. These will be discussed further in the impediments section of this paper. Even though green roofs compete with many infrastructure alternatives there are so many benefits associated with green roofs to society as a whole that it is hard to actually measure the total benefit of a green roof. This makes them a harder sell than other green infrastructure projects that are cheaper and whose benefits could be measured more easily. The allies and strategies needed to implement this project will be discussed further in the Allies and Strategy section of this paper.

The Draft District of Columbia Stormwater Management Guidebook defines a green roof as “practices that capture and store rainfall in an engineered growing media that is designed to support plant growth.”^[20]  Green roofs are designed to capture, retain and release stormwater runoff in a way that is sustainable and good for the environment. Green roofs have only recently been studied as a tool for reducing stormwater runoff, so the research on what type of green roof is most cost effective is still on the table. Even though green roofs are only now becoming popular in North America, they have been around for centuries as a way to insulate a building and increase a roof’s lifespan. In fact a green roof increases the lifespan of a roof by at least 20 years.^[21] Green roofs also help to save on cooling and heating costs, and absorb stormwater runoff. Absorbing stormwater runoff helps to eliminate pollutants in the runoff and prevent CSO’s. Green roofs provide new habitats for wildlife, creating a small sustainable ecosystem in an urban environment. Green roofs also provide an aesthetically pleasing roof top that might increase the property value of the building, especially if a landlord is marketing the building as a green building. Certain types of green roofs can also act as an urban farm, creating agricultural possibilities in an urban environment. Finally if green roofs are clustered together they can mitigate the heat island effect that plagues urban environments.

Green roofs might seem like simple rooftop gardens, but they are pretty complex. A green roof is comprised of up to eight layers. The lowest layer is the deck layer which is comprised of, “concrete, wood, metal, plastic, gypsum, or a composite material. The type of deck material determines the strength, load bearing capacity, longevity, and potential need for insulation in the green roof system.” A leak detection system can be installed above the deck layer, which would help to identify leaks in the waterproofing layer, but is optional. The second layer is the waterproofing layer, which is required on all green roofs. The waterproofing layer can be made out of many materials, but it must be waterproof. The third layer is the insulation layer, which can be installed below or above the waterproofing layer. This layer increases the energy efficiency of the building. The fourth layer is the root barrier layer, which prevents the waterproofing layer from being penetrated from a plants roots. Many types of materials can be used for this layer as well. The fifth layer of a green roof is A drainage layer that is “placed between the root barrier and the growing media to quickly remove excess water from the vegetation root zone. The selection and thickness of the drainage layer type is an important design decision that is governed by the desired stormwater storage capacity, the required conveyance capacity, and the structural capacity of the rooftop.” The drainage layer can be constructed using many different methods with varying types of materials. The sixth layer is usually a semi-permeable surface that prevents the growing media from clogging up the drainage layer. The seventh layer of of “an extensive green roof is the growing media, which is typically 3 to 6 inches deep (minimum 3 inches). The recommended growing media for extensive green roofs is typically composed of approximately 80% to 90% lightweight inorganic materials, such as expanded slates, shales or clays, pumice, scoria, or other similar materials. The remaining media should contain no more than 20% organic matter, normally well-aged compost” Finally the eighth layer of of a green roof is the actual plants, which are usually slow growing sedums.^[22]

 

The solution is big, but at the same time it can be implemented by the government without spending much money at all, since most of or all the cost would be placed on the private building owner. Instead, NYC would have to pass laws and implement regulations. This would include more incentives to build green roofs, and a city wide mandate for green roofs on all new construction in the city. The incentives are already underway and the mandate seems like it might be implemented far into the future as the technology evolves and the costs of construction decrease in the future. Many building types might not fall into the mandate, but it would not surprise me if in a few decades the city government did not mandate at least some type of green infrastructure for rooftops in NYC. In fact, in 2009 the city of Toronto almost mandated green roofs on certain kinds of buildings.^[23] As of now, the NYC’s government is on track, following the green infrastructure movement, by at least experimenting with green roofs in a number of facilities and municipally owned buildings.^[24] This is not to say that NYC leads the nation or world in terms of square feet of green roof. It is Chicago which leads North America, with over 600 green roofs as of 2009.^[25]

One of the solutions that has already been implemented is a tax abatement for all buildings with NYC approved green roofs. The tax abatement is only for one year though and it is $4.50 per square foot of green roof, with a maximum abatement of $100,000 or the buildings tax liability. The green roof must cover at least 50% of the rooftop. The vegetation layer must be covered 80% by green roof. A NYS licensed and registered architect, engineer, landscape architect or horticulturist with the proper accreditations must certify the green roof in order for the building owner to receive the tax abatement. The green roof must also have a weatherproof & waterproof roofing membrane, a roof barrier layer, an insulation layer, a drainage layer and a growth medium. If the soil is less than 3 inches deep it needs an independent water holding layer, which would prevent the plant from drying out, unless the green roof is certified to not need this layer. There must also be a comprehensive maintenance plan that includes semi-annual inspection, plans for plant replacement, monthly inspections of drains and a guarantee that the maintenance of the green roof will be maintained for a minimum of four years after the tax abatement is granted.^[26],^[27] All these regulations are impediments to building owners trying to get the tax abatement, but they are necessary, since there needs to be some standards for the tax abatement, since the environmental benefits of a green roof should be maximized. In fact, these regulations could be worse. They could require a certain soil depth or vegetation. These regulations seem to me like they are well thought out, but further regulations would be too constraining for building owners and green roof installation companies.

In order to incentivize green roofs more I believe another smaller tax abatement should be given for every successive year after the initial tax abatement. This would reflect the nature of green roofs and how they add a positive economic externality for society. Most of the costs lie on the building owner or developer, even though green roof benefits all of the community by decreasing pollution caused by CSO’s and stormwater runoff. Even though the cost of the installation and maintenance of a green roof falls heavily on the developer or the building owner, the benefits that a green roof has on society means that a green roof acts as a positive externality. A positive externality defined in economic terms is, “when an individual or firm making a decision does not receive the full benefit of the decision. The benefit to the individual or firm is less than the benefit to society.”^[28] For green roofs this is true because, “Essentially, cities are going to benefit more than any individuals will benefit because it will save with infrastructure costs,”^[29] In order to solve the problem of a positive externality the government has to incentivize consumers to buy more of that product by giving a subsidy, which can be in the form of a tax abatement. This has been implemented, but longer term tax abatements would incentivize building owners to keep their green roofs and maintain them well beyond the four year minimum that the current tax abatement regulations require.

One thing the government could find out through the use of data analysis would be the average socio economic benefit that a certain type of green roof would have every year. The city government could then give the building owner a tax abatement equal to the socio economic benefit of the green roof every year. The factors that would go into making this scale are hard to measure in actual dollars, since it is hard to measure what the dollars saved in pollution clean up efforts and flood damage, as well as the potential cleaner waterways, which could lead to economic development through tourism and development and business along the waterfront. Even though this is a problem, a scale could be created providing a tax abatement based on the water retention ability of the green roof, which is correlated with the depth of the soil. This would incentivize building owners to build a green roof if they have not already, as well as incentivize building owners that already have green roofs to continue to maintain them.

Green roofs have been built in a number of locations on top of municipal buildings throughout the five boroughs. One green roof is on the Parks & Recreation Department’s Five Borough Administrative Building, containing 25 separate vegetative systems, covering over 29,000 square feet of the roof. The number of vegetative systems allows the Parks Department to experiment and see what systems work the best and under what environmental conditions. The Parks Department website even has 15 minute interval live data and pictures of the green roof. The data can even be read in graphs in order to compare the precipitation, temperatures and moisture of each modular. One can even compare the temperatures of the air, vegetation, untreated roof and soil.

After examining the data from the rooftop on the Five Borough Administrative Building it was apparent that the untreated rooftop was much warmer during the day than at night, sometimes varying by about 30 degrees Fahrenheit at peak temperatures. This data shows the green roofs are useful for other things than besides stormwater management. They cool the roof, by absorbing sunlight, while the soil maintains about the same temperature as the ambient air in the modular vegetative system with 4 inches of soil. The 6 inch and 12 inch soil modular vegetative systems have even cooler soil systems. The cooler soil means that the vegetative layer would combat the heat island effect that causes the city’s rooftops and streets to reach higher temperatures than the air above the city.This becomes more apparent and measurable as green roofs are clustered. This benefit of green roofs could help save on cooling costs during the hotter months and if green roofs were ever to become widespread it would keep the city at cooler temperatures. Green Roofs can lead to a decrease in cooling costs in the summer. For example in a scientific study that examined different types of rooftops , “Where black and white roof membrane temperatures reached 68 degrees Celsius and 42 degrees Celsius respectively in mid afternoon on a warm day when ambient air temperature reached 33 degrees Celsius, equivalent green roof membrane temperatures ranged between 31-38 degrees Celsius,” (Simmons, p. 343).^[30]  This means that the membrane reached a temperature approximately the same as ambient air, while the black asphalt was almost double the temperature of the ambient air, and the white roof was about 21% hotter than the green rood’s membrane. The Green roof was less than half the temperature of a black roof on the same day, and substantially less than the temperature of the white roof. It is important to remember that the membrane of a green roof is located below the soil. A case susty in Athens of a green roof showed that the top floor of a building with a green roof that covered 52% of the surface area of the roof saved over 50% on energy costs on the top floor of the building during the summer months and contributed to a total of 9.6% in savings on air conditioning costs and a 4.4% decrease in heating costs during the winter months.^[31] Green roofs therefore are able to decrease energy costs both in the summer and winter months of the year.

There are so many different ways of building a green roof, including monolithic, modular and substrate, that it is hard to tell which designs are better for retaining runoff and decreasing temperatures. “The technology underlying green roofs is complex, comprising many abiotic (substrate depth, weight, and composition, drainage layer and root barrier design) and biotic (plant species composition, substrate chemistry, and water availability) variables,” (Simmons, p. 339 – 340).^[32] A study titled, Green Roofs are not created equal,  studied the stormwater retention and temperature of green roofs under different conditions. The study found that green roofs and white roofs are both effective at decreasing temperatures of roofs, but that different types of green roofs absorbed stormwater runoff differently. The study comes to the conclusion that, “green roofs can retain significant amounts of rainfall, however this is dependent on the size of the rain event and the design and can fail if not designed correctly. We suggest that as green roofs vary so much in their design that they must be designed according to specific performance goals,” (Simmons, p. 347).^[33] There is a basic formula to follow to predict the storage volume of a green roof before it is installed, but it is long and complicated. But, it is always certain that certain types of soil, soil depths and vegetative layers will retain more water, insulate the roof, protecting it from the cold and decrease cooling costs. One of the biggest differences between different green roofs is the depth of the soil. According to the Draft District of Columbia Stormwater Management Guidebook, extensive green roofs, “have a much shallower growing media layer that typically ranges from 3 to 6 inches thick,” while intensive green roofs, “have a growing media layer that ranges from 6 to 48 inches thick.”^[34] Most green roofs are extensive, since they are cheaper to install and designed to be easy to maintain. Extensive green roofs mostly use a vegetative layer of sedum, which is a desert plant that can survive in drought, absorb water quickly when it rains, withstand strong winds and is extremely easy to maintain. Intensive green roofs use can have many types of vegetation, including shrubbery, trees and bushes. The difference between intensive green roofs and extensive green roofs seems cut and dry, but standards vary slightly. According to one source an intensive green roof has 7-24” deep of soil, while extensive 3-5 inches. Semi-Intensive green roofs have a soil depth of 5-7”. Extensive green roofs use sedums, moses, some grasses, succulents and herbs. Semi-intensive green roofs use plants such as selected perennials, sedums, ornamental grasses, herbs and little shrubs. Intensive green roofs use plants such as perennials, lawn, putting green, shrubs and trees, rooftop farming. Intensive and semi-intensive green roofs can be used for rooftop gardens and parks, while extensive green roofs main purpose is to retain stormwater runoff, as well as decreasing heating and cooling costs^[35]

Overall, it looks as though some green roofs are able to effectively retain water, as well as decrease the temperature of a roof, saving on cooling costs in hotter environments. According to the study, water retention for one green roof in particular was 88% as compared to another which had a retention rate of 26% after 12 mm of rainfall.^[36] If every roof in the city was able to have a similar water retention rate of 88% after 12 mm of rainfall, than the stormwater runoff problem and CSO’s that impact NYC would be mitigated tremendously.  The NY Times is quoted as saying that, “Green roofs, for instance, absorb as much as 70 percent of the rain that might otherwise overwhelm the city’s sewage system during heavy downfalls…”^[37] But, there is no easy way of getting every roof on the city to have a green roof, instead the goal is smaller. It is to advocate for green roofs and incentivize developers and landlords to build green roofs for their buildings. This would be done through a marketing plan and lobbying effort. Combined with other infrastructure developments, including retention tanks, bio swales, and porous pavement, green roofs can be a poster child of the green infrastructure movement.

The state plans on spending $1.5 billion in NYC on green infrastructure over the course of the next twenty years. Green infrastructure includes permeable services, green roofs, and bio swales.This includes $2 million that will immediately be used for demonstrations in three neighborhoods across NYC. According to the 2011 update of the NYC Green Infrastructure Plan, ‘Together with conservation measures and operational improvements, the widespread adoption of green infrastructure can reduce more CSOs at less cost than second-tier “grey” infrastructure. Moreover, green infrastructure projects provide many quality-of life benefits to New Yorkers, by improving air quality, increasing shading, increasing property values, and improving our streetscape.”^[38] The mayors 10 year capital plan allocated an additional $735 million to green infrastructure. There is also a Green Infrastructure Task Force comprised of various city agencies. In 2011 the city gave out $3.8 million in grants to private property owners and community groups to invest in green infrastructure. In 2012 the DEP came up with a new rule that requires all new construction and major alterations to an existing site to capture more stormwater runoff than was previously required. This forces private property owners to invest in green roofs, blue roofs, rain gardens and other stormwater retention techniques.

One of the main reasons green roofs is the solution for this paper is because of the fact that it is not paid for by the city or state, which means through the combination of a marketing campaign and lobbying initiative, it can be advocated for successfully and paid for by private building owners. It would only take a small amount of money to start this campaign. The campaign would achieve some credibility if a expert in the field were to endorse the campaign and join the non profit. Experts could be horticulturists, landscapers, architects, and engineers that are certified to install and certify green roofs in the NYS region.

Eventually with enough funding there could be the possibility of creating a green roof installation company that could mitigate the cost of green roofs in NYC, which are much higher than anywhere else in the country and the world. This is because of the cost of transportation, construction materials and labor, which are higher in NYC than in places like Chicago and Toronto. This also stands in vast contrast to Germany, “where an entire service industry has evolved in response to green rooftop development and costs run between $8 and $15 per square foot.” This is in conrast to NYC, where it costs about $30 per square foot to install a green roof.^[39] Most green roof installations are custom jobs, which cost more than the mass produced green roofs of Germany. Because of the higher demand in Germany (12% of all roofs in Germany are green roofs) green roofs are cheaper and knowledge and competition between green roof installation firms is greater.^[40] Therefore the best way to decrease costs in NYC is to increase demand for green roofs. Since it might be that, “A potential client may still lack a thorough understanding of the direct, tangible and long-term economic benefits of building a green roofing system,” there must be a campaign to spread knowledge and awareness of green roofs before new cheaper and faster installation methods are developed.^[41]

Impediments

There are a few reasons why green roofs have not taken off as fast as some would have liked. The technology is not yet widely available, the cost is high, there is bureaucratic red tape involved in getting a green roof certified and there are other green infrastructure alternatives that are potentially cheaper and more effective. It is hard to tell whether any advocacy campaign will kick off without more support from the government. Even though there are plenty of impediments preventing green roofs from becoming widespread, they are still increasing in popularity. It seems that green roofs will become more common, but not everywhere. What is more likely to happen is green roofs being installed on municipal buildings, but more importantly installed on luxury residential buildings and condominiums.

It is important to realize that even though green roofs will be the main focus of this paper and project, it is not the only solution to CSO’s or rising energy costs and consumption. For example New York and other cities have built “retention basins — tanks that hold sewage until the water volume has eased. Others have reconfigured treatment facilities to expand and maximize flow rate. Still others cities have embraced “green infrastructure” — green roofs, porous pavements and so-called bioswales, or planted ditches that filter contaminants — to reduce the amount, speed and toxicity of water drainage after a storm,” (Ascher, p. 1).^[42]

The publicly funded projects like retention bases and bioswales can be very expensive to build, costing tens of millions of dollars. Another problem is that retention tanks are disruptive to build. They are disruptive because they and take up a relatively large piece of space. A retention pond is basically a large ditch that holds excess stormwater runoff. Bioswales on the other hand are not as disruptive as a retention pond. Bioswales are essentially small or medium sized gardens on the curb of the sidewalk, using special soil and plants that absorb water easily. While water is running downstream in a gutter, before it reaches a catch basin, it is diverted to the bioswale which absorbs the water. If the bioswale is at capacity it releases the water on the other side of the bioswale.^[43] Bioswales are cheaper than green roofs when comparing the dollar cost of installation with the per square inch of precipitation absorbed. Even though this is true there is still reason to build green roofs because there are other environmental, aesthetic and financial benefits of green roofs.

Green roofs are a great addition to the water management mix, but there are two cheaper options of green infrastructure alternatives that can be installed on a rooftop other than a green roof. Not everyone can afford a green roof, since they are expensive. If the building owner cannot afford a green roof, a blue roof would also work and a cool roof would also be an option. A blue roof uses permeable gravel or other permeable surfaces, while a cool roof is a highly reflective white roof, reflecting sunlight, decreasing greenhouse emissions and cooling costs. A blue roof is even more new to the water management mix than green roofs are have only implemented on a few municipal buildings’ rooftops and some private buildings.^[44] Cool roofs on the other hand are directly competing with green roofs and have skyrocketed in popularity. NYC promotes cool roofs more than it does green roofs, since the NYC government has its own website dedicated to information on cool roofs, while information on green roofs is divided between respective agencies like the DEP, Parks Department and Buildings Department..^[45]

A cool roof does not help prevent stormwater runoff from entering the combined sewer system, but at least it is a more sustainable option to a traditional tar roof.^[46] Tar roofs are actually bad for the environment, since the black tar traps heat quickly, making the building hotter, leading to increased cooling costs for the building. A white roof reflects more sunlight than a traditional tar roof. Cool roofs might not have any benefits regarding stormwater management, but they are known to cut air conditioning costs by 20% or more during hot and sunny weather. A green roof on the other hand leads to temperatures that “are up to 30 percent lower during the daytime in the summer than they are on those with conventional roofs.”^[47]  Cool roofs also cost as little as 15% more than a regular tar roof.^[48] A green roof’s cost varies, but it is much more expensive than a cool roof, costing more sometimes more than $30 per square foot, especially if it is being installed in the city.^[49]  “Art Rosenfeld, a member of the California Energy Commission who has been campaigning for cool roofs since the 1980s, argues that turning all of the world’s roofs “light” over the next 20 years could save the equivalent of 24 billion metric tons in carbon dioxide emissions.”^[50] Even cool roofs have their limits though, since scientists understand that in many colder cities like Detroit or Minneapolis, a cool roof might increase heating costs more in the winter than they decrease cooling costs in the summer.

The high cost of a green roof is offset by the tax abatement that was supposed to lead to the installation of more green roofs in the city, but there are fewer green roofs in New York than in other cities because the government and private building owners have realized the cost of installation is not worth the benefit. For example a senior policy adviser  in New York City’s long-range planning and sustainability office said to a panel at the Harvard Club of New York that, “We found that street trees are more cost-effective than green roofs.”^[51]. The cost is also a big pill to swallow for building owners, even with the tax abatement. For example, “Because of high labor and transportation prices in New York, green roofs can cost as much as $30 a square foot to install in the city, up to three times more than in other places. While the environmental benefits of green roofs are real, builders have had a hard time justifying the extra cost when it is unclear how it will affect their bottom line.”^[52] This goes to show you that it would be hard to justify the cost of a green roof for everyone. There are strategies to counter this impediment though, including the possibility that a landlord can raise their property value and attract tenants who are concerned with the environment. This will be discussed further in the next section of the paper on Allies and Strategies.

There are many technical and engineering hurdles that must be overcome when installing a green roof. For example, to install an extensive green roof, the roof itself must be able to support an additional weight of 15-30 pounds per square foot (psf). A green roof can optimally retain water when the roof itself is at a pitch of 1-2%. Anything steeper and some of the stormwater runoff will not be retained in the soil and vegetation. A pitch of above 30% is considered a green wall, which does not support the same level of stormwater retention as a green roof. A green wall can be used to receive cistern discharges. This means that some stormwater can be held in a manufactured cistern and slowly discharged into the soil and vegetation of a green wall. Another hurdle to overcome is the transportation, storage of materials during installation. There must be easy access to the roof, or else additional installation costs may be incurred. For example, if there is not a wide enough entrance to the roof than a new entrance might have to be installed or a crane used. Green roofs also pose a fire hazard. A BMP that is recommended is a 2 foot wide vegetation free zone along the perimeter of the roof, with a one foot wide vegetation free zone along all protrusions along the roof. This acts as a fire break creating a safer green roof that is not at risk to fire caused by damaged electrical and heating, ventilation, and air conditioning (HVAC) systems along the roof. ^[53]

Green roofs vary in soil depth. A deeper depth of soil means that more water can be retained. A greater soil depth would also mean less watering. For example in a study titled, Watering Regime and Green Roof Substrate Design Affect Sedum Plant Growth, “water was required at least once every 14 days to support growth in green roof substrates with a 2 cm media depth. However, substrates with a 6 cm media depth could do so with a watering only once every 28 days.”^[54]

The types of plants in a green roof also have a large part to play. Some vegetation absorbs water faster, other types can live all year long, and still others can survive without water for a longer durations of time. Many green roofs use the genus, sedum, which is resistant to droughts. Sedum is also resistant to high levels of water saturation. A study titled, A Zero Discharge Green Roof System and Species Selection to Optimize Evapotranspiration and Water Retention, tested a green roof located in the Bronx which used two local plants, ( Spartina alternaflora and Solidago canadensis) of the genus sedum. The findings, indicated that both species can tolerate the extremely dry and completely saturated conditions of the roof, as well as being capable of attenuating a 2 year storm event without drainage.”^[55]

Other studies have argued that using one plant type is not the way to go. For example a study titled, Planting Options for Extensive and Semi-Extensive Green Roofs, suggests that “The three main benefits for widening the range of plant species used for green roofs, including native species are: Improved functional performance, enhanced conservation and biodiversity, and improved aesthetics.” The study explains that plants that root out into the substrate, are low lying, and drought resistant are optimal for green roofs. If these best practices are followed then the green roof will be less susceptible to wind damage and drought. This means less maintenance and less cost.

There are no people that are against green roofs. The government is actively playing a role to promote green infrastructure and has even started to build a few green roofs in the city. The city has also given grants to private property owners and community groups to build green roofs. The main enemies are cost, ignorance and inaction. The cost of a green roof is too high for some. There is also a limited number of experts on green roofs and limited choices for installation. Finally, people might refuse to build a green roof just because they do not feel like going through all the red tape.

The property tax incentive offered by the city to property owners who have roofs that meet the criteria for a green roof status is a great way to incentivize property owners to install green roofs. Since green roofs create positive externalities, but require high fixed cost, there is less incentive for a property owner to install one. The grants given out so far are also a good way to kick start interest in green roof infrastructure. Unfortunately I could not find a low interest loan program that helped property owners eat the initial cost of a green roof. Surely a well designed green roof will raise the property value of a building, which means that the property owner could make back their fixed cost over time.

Another enemy is ignorance. There will be a day when everyone in the country knows what a green roof is, but it is still a term that is barely recognized by people. When most people think of green roofs they think of rooftop gardens. Most people assume that a green roof is a luxury item reserved for the tops of luxury condominiums and penthouses. Green roofs though have a purpose other than aesthetics. They are a form of sustainable urbanism that has multiple functions that include environmental, aesthetic and functional elements.

Finally there is the issue of red tape. In order to have a green roof and still receive a tax abatement a property owners  must comply with certain standards, must receive frequent inspections. The initial cost of installing a green roof will most likely outweigh the one year property tax abatement. These regulations are not too strict, but to require certification and inspections of the green roof.

Allies and Strategies

So far the general consensus on green roofs is that building a green roof might have a high financial cost to the building owner, but that the inter related environmental and economic benefits of a green roof have so far proven that green roofs are a good investment for NYC as a whole. Many infrastructure alternatives are cheaper and more effective in one or two particular areas. For example, a cool roof is almost as effective as a green roof at lowering cooling costs, but at a fraction of the cost of a green roof. Bioswales are a cheaper option for filtering and capturing stormwater runoff than green roofs are, while also providing the same natural habitat that a green roof would provide. Bioswales and retention ponds are much cheaper than green roofs at capturing stormwater runoff. The government could not simply force building owners to build green roofs on their buildings. It would take years before any major progress took place. The most important thing to remember though is that green roofs are a good long term investment for the city and property owners. In this section of the paper I will explain how green roofs, with all the impediments facing them, are still strategically viable as a green infrastructure alternative. These strategies include the use of green roofs as a marketing tool for landlords looking to attract environmentally conscious tenants. This could help to raise property values. Another strategy is to eliminate the ignorance about what green roofs are and spread the knowledge of their benefits. This way future tenants actually want to live and might seek out a building that has a green roof. Thirdly, green roofs can be used for urban agriculture. Urban agriculture is only viable on top of roofs with strong structural support, since urban farms are a type of intensive green roof and weigh more than traditional extensive green roofs. Finally in order to get passed the bureaucratic red tape, the nonprofit formed could provide certification and maintenance, as well as submitting the regulation, free of charge for anyone that uses that company to install a green roof.

It Is important to note  that plants are more visually attractive than a tar roof top, improving the aesthetics of the green roof. It is unlikely that a functional green roof would be able to rival a park’s towering trees, vistas, and but green roofs can be beautiful in their own way. They are functional pieces of urban sustainability, but at the same time they are gardens. Green roofs have the potential to introduce urbanites to nature in a new way. Green roofs can potentially offer tenants a new way to experience their roofs. Implementing Wi-fi, seating, and creative landscaping can make a green roofs semi-public spaces that have a value that is measured not only by stormwater retention and energy savings. Landlords can use this benefit to draw tenants in and have the close a lease. Green roofs are a perfect marketing tool for landlords to use when attempting to draw tenants who want a rooftop space or a garden. Green roofs could become what front lawns are to house owners. At this point in time green roofs mostly located on luxury residential buildings, but they could one day become more mainstream, as demand for more green space in urban environments continues.

There needs to be a way to eliminate the ignorance of green roofs and to make them a popular thing. One way could be through a promotional effort with the Parks Department, capitalizing on the popularity of Manhattan’s latest park, the High Line. The High Line is a 1 mile long park build on an old abandoned elevated subway line. The park is only a few dozen feet wide. It is almost like a green roof in the fact that it is high up. An advertising campaign that spread the word about green roofs to the public could help to increase demand and knowledge about green roofs. A commercial for the campaign could be something like this, “NYC’s Green Roof” (Show video clip of highline). “Wouldn’t you want a park on your rooftop?” A slogan for the campaign could be, “Why walk to the park, when you all you need to do is take your elevator!”

The Brooklyn Grange is an urban farm, which is a type of intensive green roof. It is the largest urban farm in the entire country and is an example of intensive green roof. The roof is extremely thick and capable of holding a lot of weight. The farm can produce over 40,000 lbs of organically grown vegetables every season. This is an incredible technological feet and is an example of how green roofs can be used in different ways.  “Roof farms have the potential to improve urban quality of life, create jobs, increase access to healthy fresh foods, and provide environmental and agricultural education to those of us who live in and love the city.” ^[56] Urban farms are great, but they require large amounts of maintenance and are best for industrial buildings with large rooftops, similar to the one the Brooklyn Grange is installed on.

Green roofs bring with them so many positive externalities that it is hard to judge their total economic benefit. Green roofs are very expensive to install and do entail some monthly maintenance costs depending on the type of green roof that has been installed. At this point in time green roofs are rare, but the knowledge, expertise and popularity of green roofs is increasing at a fast pace. It might only be a matter of time before they become standard on new buildings. Many green roofs have been installed on municipal buildings, as prototypes and examples of their potential. These green roofs are designed by experts who are hired or work for government agencies. As the technology becomes more widespread and the demand for green roofs increases over time, more private entities will emerge in the market to quench the thirst of demand. Hopefully this will lead to an influx of green roof installations across cities all over the world. After the infrastructure and technology is acquired, all that needs to happen is for urban planners, community advocates, politicians, developers, and the public to become aware of the numerous benefits that green roofs offer to cities and the people that live in them. Something that is already developing now and can be refined in the future is the cost of installation. If private installation companies choose to compete they will probably develop new and innovative approaches to the design and installation of green roofs, which will lead to lower installation costs and shorter installation times. Manufactured soil that can absorb more surface runoff per square inch, and genetically engineered plants are already starting to be experimented with by municipalities around the globe.

Hand off / Conclusion

Green roofs provide so many benefits that it would be hard to imagine that they do not continue to grow in popularity over time. Green roofs, as described in the solutions section of this paper provide the mitigation of CSO’s, filter stormwater runoff, help to alleviate flooding, provide a natural habitat for wildlife, increase the longevity of a rooftop, decrease heating and cooling costs, and even mitigate the effects of the urban heat island effect when clustered together. Unfortunately, I do not have the time, resources, or expertise to form a non profit dedicated to the awareness and installation of more affordable green roofs. I expect that as the information on green roofs becomes more readily available and the popularity of green roofs increases private and non-profit companies will jump at the opportunity to come up with a cheaper and faster way to install green roofs in the city, the same way companies in Germany responded to the high demand of green roofs there. Since green roofs are a new development in the infrastructure mix there is plenty of studies on green roofs and their effectiveness, but the information is scattered. Hopefully the government or a non profit can mass this information, distill it for building owners and provide an easy centralized way for people to understand the potential benefits of a green roof.

I found it difficult to obtain information on the measurable effectiveness of green roofs, since every green roof is different from the next. If companies started to guarantee energy cost savings than there might be more incentive to build green roofs. What is most important though, and what would incentivize property owners to build a green roof even more would be if the government made the tax abatement possible for every year the green roof is maintained. Even if the yearly tax abatement is less than the current one year tax abatement, it would incentivize building owners to maintain and install green roofs throughout the city.

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