By: William Davis green roofs
March 24, 2021
NYC is home to more than 1.6 billion square feet of roofing, and green roofs and solar panel systems can help reduce our greenhouse gas emissions and reduce our carbon footprint. With NYC’s vow to be carbon neutral by 2050 in mind, installing a green roof and/or a solar panel system on your building will bring us one step closer. Green roofs have vegetation that absorb stormwater, provide insulation, and combat the heat island effect, where urban environments can be warmer than surrounding areas.
If you are a building owner and are seriously considering installing a green roof on your building, we highly recommend that you hire a licensed professional to perform the work; the installation of a green roof or solar panel array may add substantial weight to a roof, and proper structural analysis, design, and installation are necessary. This analysis will help determine if the existing roof and its structure can support the added load without modification. When filing the construction permit application, the Professional Engineer (P.E.) or Registered Architect (R.A.) must certify specific technical elements, submit the structural analysis, and confirm that the existing roof will be able to support the green roof when saturated with the weight of moisture.
It should also be noted that tax incentives are available for making these improvements. However, a green roof’s design must meet specific requirements to be eligible for property tax abatement. It must have a layer of vegetation covering at least 50% of the rooftop, and sedum—or drought-resistant—live plants, must be spaced to cover at least 80% of this planted layer. In addition, a New York State licensed Professional Engineer, New York State Registered Architect, and New York State licensed and registered Landscape Architect or Horticulturist must prepare a four-year maintenance plan.
Per the NYC DOB, effective November 15, 2019, an amendment of the 2014 Administrative Code and Chapter 15 of the New York City Building Code requires new buildings, and new roofs resulting from enlargement of existing buildings, and existing buildings replacing an entire existing roof deck or roof assembly to be provided with a sustainable roofing zone, 100% of which must be a solar photovoltaic electricity generating system, a green roof system, or a combination thereof. Some of the terms used here can be confusing, so the DOB has provided the following clarifications:
- A “sustainable roofing zone” is defined as areas of a roof assembly where a solar photovoltaic electricity generating system, a green roof system, or a combination thereof, is installed.
- A “roof assembly” is a system designed to provide weather protection and resistance to design loads. The system consists of a roof covering and roof deck or a single component serving as both the roof covering and the roof deck. A roof assembly includes the roof deck, substrate, or thermal barrier, insulation, vapor retarder and roof covering.
- A “roof deck” is the structural surface to which the roofing and waterproofing system, including insulation, is applied. A typical roof replacement project where minimal roof deck replacement is required does not require the installation of a sustainable roofing zone.
The code also states that the following areas are excluded from the sustainable roofing zone:
- Areas required to be set aside for setbacks or access pursuant to the New York City Fire Code, New York City Construction Codes or the Zoning Resolution of the City of New York. For example, rooftop access areas required by Fire Code section 504.4 and 512.3.1 that must be kept clear are excluded from the sustainable roofing zone.
- Areas occupied by rooftop structures, water towers, greenhouses, mechanical equipment, towers, antennas, parapets, guardrails, solar thermal systems, equipment access pathways and appurtenances.
- Areas occupied by obstructions related to stormwater management practices including, but not limited to, cisterns, or reuse systems that are installed to comply with site connection or stormwater construction permits issued by the Department of Environmental Protection.
- Building setbacks, including terraces that are existing non-complying pursuant to the New York City Zoning Resolution, or that are voluntarily provided. However, each setback must comprise less than 25 percent of the area of the largest floor plate in the building.
- Recreational spaces that are integral to the principal use of the building on which the rooftop is located, including but not limited to playgrounds and participant sport areas for sports facilities and schools, Quality Housing recreation spaces, roof terraces and passive recreation areas that are documented on the certificate of occupancy or Department of Buildings approved filing as outlined in Building Bulletin 2018-002.
- Pitched roofs (roof slopes greater than 17%) that would accommodate less than 4kW of solar photovoltaic electricity generating capacity. Supporting documents, including calculations and shading report by a qualified contractor or NYS registered design professional, must be submitted.
- Areas where site conditions are determined to be unfavorable to either a solar photovoltaic electricity generating system or a green roof system. For example, in cases where the entire roof assembly including roof deck is replaced, but the building structure cannot support the added weight of a sustainable roofing zone, a statement by a NYS registered design professional shall be submitted to the Department to substantiate the practical difficulty due to structural limitation.
Construction documents consisting of roof plans depicting a code compliant sustainable roofing zone must be submitted to the department; these plans must show the included and excluded areas of the sustainable roofing zone, as well as clear indications of Fire Department access areas. Additional information such as drawings showing anchorage, details, diagrams, and tabulation of areas included and excluded from such zone should also be submitted. A statement by a qualified Contractor or NYS registered design professional shall be included on the plan to indicate the anticipated solar generation capacity of the sustainable roofing zone. Where the required capacity cannot be met, calculations or shading report prepared by the qualified Contractor or NYS registered design professional shall be included on the roof plans. Rooftop photovoltaic and green roof projects may be filed as part of another New Building or Alteration permit application. They may also be filed separately through the borough offices or through The HUB Full Service as an Alteration Type-2. All solar electric projects must file an Electrical permit application.
If your building has a roof replacement project on the horizon and you are considering installing a green roof or solar panel system, please feel free to reach out to Sullivan Engineering with any questions!