Understanding Future Uses of Roofspace and Defining An Early Path to Profitable Roof Estate Investing
December 8th, 2011
Via Columbia University’s State of The Planet blog, an interesting article examining the enormous stormwater capture capabilities of Green Roof systems. As the report notes:
Green Roofs are becoming increasingly popular in New York City for their numerous environmental and economic benefits. Economically, they can lower energy costs through added insulation and lowered air conditioning costs, protect new or existing rooftop membranes for decades, and increase property value through added living space. Environmentally, Green Roofs capture stormwater, reduce the urban heat island effect, reduce particulate matter in the air, and provide habitat for pollinators and birds. They can also be a source of local agricultural production.
Native Green Roof in Red Hook, Brooklyn
Recently, New York City has realized the enormous stormwater capture capabilities of Green Roof systems. The City has been promoting the use of Green Roofs in both the public and private sectors through generous tax incentives and various funding opportunities. In a city so densely populated, old combined sewer systems overflow frequently polluting the waterways. Green Roof technologies are being adopted as a primary tool to combat some of New York City’s largest environmental issues.
New York City Combined Sewers
About 150 years ago, with a population of around 1 million people, New York City began building a comprehensive combined sewer system to cope with its’ stormwater and wastewater. At the time, captured waste and storm water would be held in the sewers and eventually discharged into the surrounding waterways. The combined sewer system provided a cleaner, healthier New York.
However, city planners never anticipated the substantial growth the city would see over the next hundred years. As populations increased and the city became industrialized, the combined sewer system infrastructure became over-burdened and inefficient. To cope with the increased populations, the city began building treatment plants in 1935, and by 1995, there were 14 facilities across the city and it’s 5 boroughs built to treat wastewater.
Now, New York City is now home to over 8 million people in an area of just over 300 square miles, and the city filled with mostly impervious membranes such as streets, sidewalks, and rooftops. As a result, during heavy rainfalls, water cannot always be contained, and it often flows freely at a rapid pace into the city’s combined sewer systems. Even with all the wastewater treatment facilities, this can easily put a heavy burden on the sewer system. The sewers cannot always cope with the massive influx of water coming from rooftops and streets, and when the sewer system reaches its’ wastewater capacity, hundreds of overflow valves throughout the 5 boroughs release wastewater into the surrounding waterways instead of flowing back onto the streets. This process is known as a Combined Sewer Overflow (CSO).
While this safety measure keeps the streets from filling with filth, the overflows do create substantial issues within the New York City Watershed. The overflow release valves are a form of point-source pollution, allowing wastewater to flow directly into rivers and creeks. The wastewater contains heavy amounts of nutrients such as nitrogen (from human waste) and phosphorus, as well as any pollutants absorbed by stormwater including oil, pesticides, industrial chemicals, and many other pollutants found on streets and sidewalks.
As a result, over the past few decades, New York City waterways have become extremely polluted with excessive nutrient loads and chemicals, making most of the waterways unsafe for recreational activities such as swimming and fishing. As part of the Clean Water Act’s goal to restore all waterways of the United States to swimmable and fishable conditions, the Environmental Protection Agency has been fining the city of New York millions of dollars year after year for failing to comply with federal waterway quality and stormwater regulations.
For a video explaining more about Green Roof Technology, please click here: Green Roof Background
The DEP Green Infrastructure Plan
One of Mayor Bloomberg’s PlaNYC 2030 initiative is to introduce alternative methods in coping with city’s current combined sewer overflows. Part of the plan is to invest $1.5 billion in Green Infrastructure projects over the next 20 years. This, coupled with traditional grey-infrastructure will reduce the amount of CSO’s by an estimated 40% and save the city (and its’ residents) over $2 billion.
NYC Mayor Bloomberg on a Green Roof installed by Highview Creations
As part of the Plan, The NYC Department of Environmental Protection (DEP) is currently funding cost-effective Green Infrastructure (GI) projects such as Green Roofs, Blue Roofs, tree-pit catchments, and street-side swales to create permeable surfaces and subsurfaces to manage stormwater. Through the use of biomimicry and ecological engineering, introducing these Green Infrastructure projects will create functional systems to retain, detain, and capture stormwater at a lesser cost than introducing solely new “grey-infrastructure” programs.
A DEP sponsored Green Roof/Blue Roof comparative study at a public school in the Jamaica Bay Watershed
The main idea behind this approach is to effectively hold stormwater before it enters the sewer system, which will alleviate a lot of the stress on the sewers during heavy rainfalls. This will decrease the amount of combined sewer overflow events and as a result, allow the treatment facilities to treat wastewater before it is released into the surrounding waterways. Green Roofs are perhaps the best approach to capturing stormwater, and come with a wide-range of other benefits too.
The Green Roof portion of a DEP sponsored comparative study
Green Roofs: The Ultimate Weapon for a Healthy City
Green Roofs provide a wide-range of environmental and economic benefits for a building owner. On average, a building owner can lengthen the life of a roof by 5 times or more because a Green Roof protects a new or existing roof from harsh weather including rain, UV rays, and direct heat and cold, which can otherwise rapidly expand or retract a rooftop , causing cracks and leaks. This can produce substantial direct savings, since the building owner will not have to pay for repairs or replacement as frequently. Green Roofs have also been known to increase property value as it increases the aesthetics of a building, and often creates additional living space.
Green Roofs also increases the insulation of a building through additional r-value, allowing more heat to be retained in the winter. In the summer months, the roof will retain cooler air inside, and not allow heat to escape through the rooftop. In normal summer months, black rooftops can reach temperatures in excess of 125 degrees (F), increasing the urban heat island affect. However, a green-roof can create temperatures at or below ambient temperatures. If an HVAC system is located on roof where a Green Roof is installed, there can be significant reductions in air conditioning costs because the AC intake is bringing in ambient temperatures. This prevents the HVAC system from working as hard to cool air, which can result in significant energy cost savings. For example, a green-roofed building owner realized a 30% decrease in AC costs after the first year a green-roof was installed using native plantings. While these results are not always typical, it does show the capabilities of Green Roof’s energy-use reduction.
The stormwater capture element of Green Roof technologies has been realized by New York City as a cost-effective approach in retaining and detaining stormwater from the combined sewer system. In a basic Green Roof system at a 3″ depth, over 50% of all annual rainfall can be captured. When it rains, engineered Green Roof soil (known as media) captures water in its’ void space. This water will be retained in the void space until the system becomes fully saturated with water, at which point, any excess water will flow to the drain. Through sun exposure and plant uptake (known as evapotranspiration), much of the water is used or released into the atmosphere as part of the water cycle. As a Green-Roof’s soil depth and porosity increases, so does the ability to capture stormwater as it increases void space.
Depending on the planting scheme, evapotranspiration rates can fluctuate. Sedum and succulent-like varieties are widely used due to their ability to withstand the harsh conditions of a rooftop environment. On a roof, there is often a plethora of direct, intense, and extended sunlight. During dry periods, this can present drought-like environments, which sedum plantings can tolerate quite well. However, their evapotranspiration rates are lower as they absorb and retain most rainwater and do not transpire as frequently. This may reduce their efficiency in cooling surrounding areas and AC costs, but are still very effective in utilizing captured stormwater.
Native and other herbaceous species are another option to Green Roof systems. While they require deeper soil depths and are not as drought-tolerant (and may require some irrigation), they are more effective in promoting local ecologies and reducing temperatures of surrounding areas. Furthermore, when woody plants are used, migrating birds have been known to utilize Green roof systems.
A native Green Roof at a public school in Brooklyn, NYC. This Green Roof is used by the school for educational purposes.
In addition to local realized benefits, Green Roofs also provide healthier surrounding areas. Part of the reason why New York City and the DEP has adopted Green Roof technology is due to their wider range of environmental benefits. Green-roofs have the ability to reduce the heat-island effect of surrounding areas, provide habitat for pollinators and migrating birds, and filter particulate matter in the air. All of these benefits create a healthier urban environment that can be noticed on a large scale. There is also an educational awareness that can provide a societal benefit as local communities can learn about the importance of local ecologies in urban settings.
This entry was posted on Thursday, December 8th, 2011 at 2:25 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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Educated at Yale University (Bachelor of Arts - History) and Harvard (Master in Public Policy - International Development), Monty Simus has held a lifelong interest in environmental and conservation issues, primarily as they relate to freshwater scarcity, renewable energy, and national park policy. Working from a water-scarce base in Las Vegas with his wife and son, he is the founder of Water Politics, an organization dedicated to the identification and analysis of geopolitical water issues arising from the world’s growing and vast water deficits, and is also a co-founder of SmartMarkets, an eco-preneurial venture that applies web 2.0 technology and online social networking innovations to motivate energy & water conservation. He previously worked for an independent power producer in Central Asia; co-authored an article appearing in the Summer 2010 issue of the Tulane Environmental Law Journal, titled: “The Water Ethic: The Inexorable Birth Of A Certain Alienable Right”; and authored an article appearing in the inaugural issue of Johns Hopkins University's Global Water Magazine in July 2010 titled: “H2Own: The Water Ethic and an Equitable Market for the Exchange of Individual Water Efficiency Credits.”