A green roof is an addition to a roof, which can help make a building more sustainable, while delivering benefits to both humans and ecosystems. The structure of a green roof includes waterproofing, root barrier and drainage systems, filter cloth, and a growing medium for plants.
The benefits of installing a green roof include insulation and reduced energy use, the removal of air pollutants and green house gases through carbon sequestration/storage, increased roof lifespan, reduced heat stress, stormwater runoff management, improved quality of health, and beautification. There are two types of green roofs—extensive and intensive. Extensive green roofs have a soil depth of 1”- 5,” and are planted with sedums and short grasses. Intensive green roofs need at least one foot of soil, along with integrated irrigation and drainage systems, and can be vegetated with trees, shrubs, and perennials. Installing an extensive green roof normally costs $10 per square foot, whereas intensive green roofs cost $25 per square foot. Annual maintenance costs for green roofs range from $0.75-$1.50 per square foot.
While the initial costs of installing a green roof are higher than for a conventional roof, the difference is easily offset by its cost-effective benefits. For example, green roofs can increase roof life span by blocking UV light. One study found that an extensive green roof reduced the energy demand for air conditioning in the summer by over 75%. There are also federal and local tax incentives for green roofs—such as the one-year property tax credit available in New York City for property owners who green at least half of their roof. Green roofs can help contribute to LEED certification, by protecting or restoring habitats, maximizing open space, storm-water quality control, reducing the heat island effect in urban areas, and increasing water efficiency.
Green roofs support biodiversity by providing a habitat for native plants, invertebrates, birds and other animals. Small-scale, local food production is also possible with green roofs, creating opportunities for communities to partake in healthy, in-season produce. Sedum doesn't absorb water or promote biodiversity as well as other species, while it is effective for lowering the heating and air-conditioning energy requirements of a building. Determining which green roof plants most support biodiversity requires finding the best soil composition for microorganisms to thrive in. Scientists are currently exploring this question. Integrating sedum with other native plants, to maximize the potential benefits of green roofs, requires creative, multi-purposed, and efficient landscape design.
An aspect of green roofs that is not talked about as much, which I have personal experience in, is their potential psychosocial benefits. I work periodically for a company called Alive Structures, helping install commercial and residential green roofs across New York City. When first spending time on green roofs, I can remember feeling surprised initially by the sense of peace that I felt. Much of the health benefits of green roofs are rooted in aesthetics. Green roofs give us something beautiful to look at and meditate on. They also reduce noise pollution, which helps enable clearer thoughts. Evidence shows that simply being around plants leads to lower blood pressure, increased attentiveness, productivity and job satisfaction, lower anxiety, and improved wellbeing. Green roofs can serve as collective spaces for individuals to cooperate and work in, while enjoying the beauty of nature together. Entomologist Edward Wilson’s biophilia (“love of life”) hypothesis partly explains why green roofs make us feel so good. According to this concept, our evolutionary heritage is what draws humans towards having a deep connection with nature. The physical and mental health benefits of green roofs have led to an increase of green roof installations at hospitals and care centers. With Alive Structures, I helped install a modular green roof at New York Hospital Queens (NYHQ) in 2012. The project at NYHQ was part of a New York City Department of Environmental Protection grant to reduce stormwater runoff. However, what I find equally exciting about the NYHQ green roof is its potential positive impact on patients and hospital staff. In the springtime, when the sedum is blossomed, new mothers and their families can now look out from the maternity ward windows, to a sprawl of color and life.
Of course, hospitals aren’t the only places that can benefit from green roofs. There’s much potential to explore the therapeutic aspects of green roofs in a variety of professional and personal spaces. The average office worker is stressed, and frankly, out of tune with nature in an unhealthy way. Humans require sunlight, fresh air, and also time to commune with nature. In the words of naturalist John Muir, “Everybody needs beauty as well as bread, places to play in and pray in, where nature may heal and give strength to body and soul.” Imagine if you had the opportunity to take five minutes away from your desk, to walk out onto a green roof. From my experience, being outside amidst living things recharges the battery and helps me work more productively. What is so promising about green roofs is their capacity to strengthen and develop the complex interrelationships between the built environment, communities, and natural world. In short, green roofs can help make life healthier for humans and the environment alike.