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green roof 1A green roof is often described as a living extension of an existing or newly constructed roof incorporating a water proof membrane and root barrier, a drainage system, lightweight soil, and plants. A green roof can not only add a beautiful green space to your home, but also increases property values while offering substantial benefits to the environment. In Brooklyn green roofs help provide insulation to a building, and reduce the volume of storm water runoff by absorbing and retaining water that would otherwise flood the storm sewer system resulting in sewage spills and overflows.

green_roof_diagramBefore starting a green roof project, the building should assess, along with a structural engineer, how much weight the structure can bear and the condition of the roof membrane. Building owners should also agree on how much maintenance they are willing to put into the longevity of the roof.

drought tolerant plantsGreen roofs are divided into three types of systems: extensive, intensive, and hybrid. The main differences are the amount of soil (growing medium), with extensive using 6” or less, and intensive using more than 6”. Hybrids might include areas of both types.  The choice between these systems is often based on load bearing capacity of the roof as well as budget, maintenance costs, visibility, and access to the roof. Costs can run $12 – $25 per square foot for an extensive green roof with no irrigation system if the existing structure is sufficient, but may cost $12- $40 per square foot for an intensive green roof if additional structure and irrigation is required.

green roof 3Case Study: Chocolate Factory Condominiums
In 2009, six years after the Cocoline Chocolate Factory building at 689 Myrtle Avenue had been converted to the Chocolate Factory Condominiums, the building elected to install a green roof. The original roof membrane on our building had been faulty since the conversion, and numerous leaks and damages had occurred. After several attempts at spot repairing proved unsuccessful, it was determined that the only solution was to replace the entire roof membrane.

green roof 4This full overhaul of the roof prompted the building’s board of managers to research several options. We realized we could repair the structural aspects by replacing the roof membrane, and for not much more we could also insulate the building, provide valuable and enjoyable green space for residents, and receive a substantial tax abatement from the city by installing a green roof.

We met several companies who offered a variety of options and solutions. We chose to work with Greensulate and Roof Services, who together had completed a number of green roof projects. At 5000 sq. ft however, our roof was going to be the largest they had undertaken in New York.

green roof 5We chose to do a hybrid green roof with a manual irrigation system. We worked with Greensulate on the design and layout of the roof to incorporate green space, a roof deck with furniture, and a walking path around the roof. We wanted the whole area to be accessible so kids could ride tricycles around, and also have an area for viewing the city skyline and fireworks displays. The existing roof had been covered with 5000 sq. ft of paver stones. Those were removed and recycled by Greensulate for other projects, and 1100 sq. ft were kept to create an elevated area for the buildings AC units.

In order to qualify for the city’s $4.50 per sq. ft tax abatement, we needed to adhere to the following guidelines:

  • At least 50% of eligible roof space must be covered by the green roof
  • A vegetation layer, at least 80% of which must be covered by live plants such as sedum or equally drought resistant and hardy plant species.
  • The 80% coverage means spacing of plants in a manner that will cover 80% of the layer by the end of the compliance period (the year the tax abatement is granted.) A New York State licensed and registered architect, engineer, landscape architect or a horticulturist with a degree or certificate from an accredited training institute, must certify the vegetative layer.
  • A weatherproof & waterproof roofing membrane compliant with construction and fire codes
  • A root barrier layer
  • An insulation layer compliant with energy, fire and construction codes
  • A drainage layer designed so the drains can be inspected and cleaned
  • A growth medium including natural or simulated soil at least two inches in depth.
  • Maintenance plan that includes a semi-annual inspection, plans for plant replacement, monthly inspections of drains free from debris and maintenance of green roof for a minimum of 4 years after the tax abatement is granted.

We were able to include all of the amenities we wanted for the building, qualify for the tax abatement, and take steps to reduce our impact on the environment.

green roof 6Greensulate chose a sedum mix, native grasses, creeping thyme, echinacea, black-eyed susans and lavender plants as the main elements of the green roof’s vegetation. They also sourced decking and walkway materials constructed from synthetic wood made of recycled shopping bags, keeping 590,000 bags out of the landfill.

The green roof has become our building’s most loved amenity, and is enjoyed year round by residents. Solar lights installed in the decking make a safe illuminated walkway for evening visits. Patio areas have increased community gatherings in the building and provide a green space otherwise lacking in our neighborhood.

green roof 7The building also received a $16,000 tax abatement from the city for complying with the green initiatives program, and was surprised to learn that that it was the first green roof in New York City to qualify and receive this tax abatement.  Since the roof system was designed in a sustainable fashion, maintenance of the roof has proven to be a small investment. It is widely agreed that the green roof is one the best investments the building has made, continues to be a source of enjoyment and pride for the building, and has sparked additional green initiatives and community building projects.

Useful Links:

Cooper Union Institute for Sustainable Design

New York City Parks and Recreation

NYC Green Roof Property Tax Abatement Program

Greensulate

Kemper System – Eco-Roof system

Goode Green

Columbia Green

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