Green Roofs FAQ

A green roof is a vegetated extension of an existing roof. Designs vary between projects but all green roofs have the same basic components: waterproofing, a root barrier, a water retention and drainage layer, a filter fabric, a lightweight growing medium (e.g.: engineered soil), and plants.

According to the Green Roof Researchers Alliance, there are approximately 730 buildings with green roofs in New York City. Of the 40,000 acres of available rooftop space, this represents only 60 acres, or fewer than 0.1% of NYC’s 980,000 buildings.

Green roofs are like a swiss-army knife solution, offering multiple benefits: improved stormwater management, enhanced biodiversity, air quality improvement, reduced urban heat island effect, improved thermal insulation, lower cooling costs, extended roof lifespan, noise reduction, aesthetic value, recreational space, and positive effects on mental well-being.

The owner’s goals for the green roof will determine the level of maintenance required. A green roof designed as a highly manicured amenity space on a luxury hotel will require more attention than one installed out of sight atop an industrial building for the purpose of thermal insulation, membrane protection and/or compliance with local mandates. But just like any other garden, even the simplest green roofs require at least some degree of maintenance throughout the year. This includes watering, feeding and weeding. If applicable, this may also include maintaining and winterizing the irrigation system. Size, geographic location, accessibility, frequency of visits, maturity of the green roof, aesthetic goals, and nature of the tasks will all determine the costs. In the greater New York area, annual costs for green roof maintenance typically range from $0.85 to $1.30 per square foot per year.

The cost of a green roof varies considerably depending on things like the overall system size and depth, plant selection, geographical location, ease of access and optional features like irrigation, decking and lighting. The overall type and intended usage of the green roof also affects its cost greatly.

Simple, shallow, 'extensive' green roofs with only the most basic elements are often installed when the roof will not be regularly seen nor accessed. Extensive green roofs are often installed to comply with local laws or to meet a design standard. Even these simple green roofs bring an array of operational benefits like roof membrane protection and reduced heating/cooling costs for the upper floors. A simple extensive green roof in NYC will typically cost between $15-$25 all-in. Again, these numbers can vary dramatically with just the size of the installation. These numbers do not yet consider any grants or financial incentives which can be quite generous.

Accessible 'intensive' green roofs designed as amenity spaces typically require a greater initial and ongoing maintenance investment to maintain their aesthetic. An intensive green roof in New York City will cost anywhere from $35 to $65 per square foot or greater. But they come with improved marketability, quality of life and property values, in addition to all the standard operational benefits offered by simple, extensive green roofs.

• The New York City government currently offers two different financial incentive programs for Green Roofs:

• The NYC Green Roof Tax Abatement program provides a one-time property tax abatement for properties that have green roofs. As the owner you will get $5.23 off your taxes for every square foot of green roof space. The most you can get is $200,000 or the total property taxes for the building that year, whichever is lower. If you have more abatement than taxes in any year, the remaining amount may be applied to your taxes within five years from when the abatement was initially taken. Properties in select priority districts will receive the Enhanced Green Roof Tax Abatement rate of $15 per square foot of green roof installed. Not sure which property tax abatement tier your building qualifies for? Use our handy Solar Map Tool to look up your building and see.

• The NYC Department of Environmental Protection’s Green Infrastructure Grant is even more generous but also far more difficult to obtain. In theory, the grant will reimburse nearly all costs associated with designing and installing a green roof on a privately-owned building inside the five boroughs. The minimum project size is 5,000square-feet. The program’s goal is to incentivize private property owners to retrofit their roofs with green roofs to manage stormwater runoff. The deeper the green roof, the more stormwater that can be managed. For this reason, reimbursements are based on system depth - the deeper the green roof, the greater the rate. Potential grantees must be willing to sign a Legal Agreement and Restrictive Covenant to participate. The designs for green roof project applications will undergo multiple design review processes for a total process duration of 12-18 months. At no point in this process is successfully obtaining the grant guaranteed so it is not for the faint of heart or anyone in a hurry. Having said that, Urbanstrong’s green roof design partners have won this grant for a number of clients.

As of 2016, more than half of green roof installations were concentrated in wealthier areas such as midtown and downtown Manhattan. More information on this can be found in this article published by the Columbia Climate School.

While the final language around NYC Local Law 97 has not yet been released, all signs point towards green roofs being an effective retrofit for compliance. Green roofs thermally insulate buildings to reduce energy required for heating and cooling. Further, by their very nature, plants absorb carbon dioxide as a critical component of photosynthesis. While other energy conservation measures (e.g.: LED lighting upgrades, duct-sealing, BMS, boiler upgrades, etc.) all indirectly reduce carbon emissions by reducing energy consumption, green roofs directly sequester carbon right at the installation site, so surely this will be factored into their compliance determinations.

• Any new construction project can create a roof suitable for a green roof. It should have ample structural support to accommodate the green roof when it is holding its maximum designed amount of stormwater, and the roof should also have plenty of roof drains, and a water and power source for irrigation and other controls. With enough money, any existing roof can be modified to meet any of the above criteria. No matter what, you need a state-licensed structural engineer to sign off on a green roof design. No exceptions.

• Depending on the building type (e.g.: single family, 1-3 family, or multi-family building) and how the roof will be used (accessible or inaccessible green roof), the roof may have to comply with different exit and egress requirements. Railings or parapets must be 42” tall from the finished roof. If the building has an elevator, or is subject to elevator requirements, at least one elevator must access the roof. If there is no elevator to the roof, one of the elevators must be extended. Or there are options to build a small lift from the top floor through the ceiling up to the roof. This requirement is for ADA Accessibility, the Americans With Disabilities Act.

• Smaller buildings with fewer units, and green roofs designed to be inaccessible and not declared as accessible areas on the Certificate of Occupancy have much more relaxed rules.