Green roofs are definitely the buzz around cities in recent years because of their great benefits for both buildings and our environment. However, when you want to take action and actually prepare to install a green roof on your building, as the Human Impacts Institute is in the process of doing, with hundreds of products out there on the market, do you know which ones suit your roof best? Don’t worry; let’s take a tour to the Five Borough Green Roof first!
The Five Borough Green Roof is located at the headquarters of the New York City Department of Parks and Recreation on Randall’s Island, NY. In the spring of 2007, the Five Borough Technical Services Division began to install green roofs on their rooftops for demonstration and experimenting purposes. Now, with over thirty types of systems and 29,000 square feet of the building covered by green roofs, it is the fifth largest green roof in New York City. Unlike any of the other known green roofs in the country, the Five Borough Green Roof is the only one that features distinct systems side by side. These systems vary by types of growing medium, depth of growing medium, and plant selection.
Artie Rollins, Chief of Technical Services at New York City Parks and Recreation, guided our tour. According to him, their green roof has become a major energy-saving tool for the building, while at the same time protecting the original roof. The plants cool the air by vapor transport. This means that the air that air conditioners suck in to cool the building is pre-cooled already, which saves a tremendous amount of energy. “ Money for air conditioners? Get a green roof!” Mr. Rollins said. The medium of green roofs’ systems is specially designed to be lightweight, weighing 25-60 lb/square feet, compared to regular dirt, which weights about 90 lb/sf. For plants, Mr. Rollins strongly recommends native plants, since they have proven to suit the local extreme weather.
There are two major types of green roofs: intensive and extensive. Intensive green roof systems require six inches or more of growing medium. They are similar to regular roof gardens that are able to support varied types of plants, from shrubs and even trees. Extensive systems, on the other hand, are much shallower, usually from two to four inches. Less than six inches of growing medium provides more ecological and economic benefits. For example, plants such as sedums, succulents, alpine-type plants, and some grasses are likely to flourish on extensive green roofs.
For the growing medium choices, there is GaiaSoil, mineral soil, Xero Flor, Container Growing Medium, regular potting soil and several others. GaiaSoil comes with various depths that are suitable for different needs. The Xero Flor, which is a technology originally from Germany and has been developed for more than thirty years, is a two to six inch green roof system, which is extremely lightweight and low cost. Regular potting soil is great for its affordability.
There are also several types of modular systems, which can be bought directly from the green roof companies and are ready to be used. Some examples include: Green Paks,BIOtrays, and Green Grid. With the Green Grid modular system, you don’t have to wait for the plants to grow; it will be fully-grown already when it’s shipped to your house.
There are also some very interesting projects taking place on the Five Borough Green Roof. One of them is the vegetable farm. In addition to its regular roof farm, they are also using Flood and Drain Hydroponics Vegetable Growth System, which is a great, innovative way to save energy while growing vegetables on the roof: “Unlike traditional gardening methods, hydroponics uses a pH balanced ionic mineral based water solution. The Tower Garden uses a closed system technology to recycle 100% of the nutrients and water while minimizing waste, which enables it to use only 5% of the nutrients and water used in conventional gardening and organic farming.”
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From Sunny Du, 2012 Human Impacts Institute Building Retrofit Intern