Solar and Green Roofs – An Unlikely Duo? 

The Climate Mobilization Act in New York City includes legislation that requires nearly all new buildings or existing buildings undergoing any major roof construction to install either a green roof, a solar panel array, or a combination of the two. The main goal of the new law is to lessen the environmental footprint of the city by reducing runoff, mitigating the urban heat island effect, and improving building efficiency. However, it is also a tremendous opportunity to dramatically expand the city’s usable outdoor space.

Until now, the majority of green roof installations in New York City have primarily been incentivized by a tax abatement and the Green Infrastructure Grant Program for buildings with significant footprints. However, the majority of buildings in New York City have relatively small footprints. When combined, these smaller buildings account for far more square footage than those of larger footprints. The Climate Mobilization Act presents an amazing opportunity for these small buildings. 

If you are weighing options for your rooftop, one compelling option is to combine both a green roof and solar panels. Highview Creations partnered with Brooklyn SolarWorks in 2019 to install a green roof and solar photovoltaic (PV) canopy project in the Crown Heights neighborhood of Brooklyn. The project demonstrated the potential to create an attractive amenity space on a small roof while realizing the best qualities of both solar panels and green roofs. 

Green roofs and solar panels may seem like unlikely partners. They are usually presented as two separate options for improving the sustainability of rooftops. However with the right arrangement, green roofs can actually enhance the performance of solar panels. The efficiency of solar PV generation declines as the ambient temperature rises. Plants on green roofs cool the ambient temperature, making them the perfect complement to a solar array. The temperature on a green roof can be 30-40 degrees cooler than on neighboring conventional roofs.

If green roofs increase the efficiency of solar panels, what (besides clean energy) do solar panels contribute? If you plan to spend hot summer afternoons on your roof, solar panels can provide an amenity that is as valuable on a rooftop as any other— shade! Lifting the solar panels up off the roof allows ample sunlight to reach the roof for plants to grow and also provides a comfortable space to hang out underneath. To account for the shade created by the solar canopy, it is important to use shade-tolerant sedum species underneath.  

When looking to install a rooftop amenity space on a small building one common challenge is access. Many roofs on smaller buildings are only accessible via a ceiling hatch and a ladder. Can your space be retrofitted to accommodate a staircase? Is access to the roof through the interior of the building desired? For the Crown Heights project, an exterior enclosed staircase was eventually installed on the back of the building. Roof access also becomes a major consideration during the installation process because of the amount of materials that must be conveyed to the roof. A site visit by a green roof professional can help to assess needs and solutions related to roof access.

As with any major project, it is also important to think about the desired uses for your rooftop space. Will the roof be accessible, and if so, what is the maximum number of people allowed to on the roof? Do you want to have furniture? What amenities, such as running water, a stove hookup, or lights, are going to be important to have? These decisions will impact steps at different phases of the project.

Lastly, the most important step before beginning any green roof project is a thorough assessment of the roof itself. Green roofs can double the lifespan of a room membrane by protecting the membrane from sun exposure. Green roofs are an excellent investment for a roof in good condition, but any issues with the roof membrane should be addressed before installation. Finally, an engineering assessment is necessary to determine allowable weight loads and is important information to have when making decisions about the solar canopy and green roof systems, and any installation that would accommodate people.

In New York City where green space is limited bare rooftops are an untapped resource. We at Highview Creations are thrilled about the ways this new law will make our city a healthier place to live. We also can’t wait to help people use this mandate to create delightful spaces they can enjoy. Combining green roofs with solar panels is an excellent way to achieve both those outcomes at once.

How can I learn more?

Do you have a roof and you’re unsure whether to go green roof or solar? Give us a call and we can talk about doing both!