Green roofs provide a wide range of benefits that help the environment, the economy, the building owner, and the municipality. Cities stand to benefit the most from green roofs because they are largely paved with heat trapping and impermeable surfaces. This poses many environmental challenges that green roofs mitigate.
1. CLEANER WATER
Everytime it rains in New York City our sewage treatment plants get overwhelmed causing raw untreated sewage to be released into the natural waterways that surround us. Green roofs absorb 70%-90% of an average rain fall acting as sponges during storms, retaining and detaining storm water that would otherwise create sewage overflow. Combined Sewage Overflow (CSO) is a serious environmental problem in New York City posing health threats to our human and aquatic populations. Green roofs have proven to be an effective tool by municipalities all over the world to reduce CSOs.
2. CLEANER AIR
According to the Toronto based organization Green Roofs for Healthy Cities a 1,000-square foot green roof can remove 40 pounds of Particulate Matter (PM) from the air in a year, while also producing oxygen and removing carbon dioxide (CO2) from the atmosphere. Removing PM from the air is crucial for reducing asthma rates in the urban environment. Forty pounds of PM is roughly how much 15 passenger cars will emit in a year of typical driving.
3. REDUCED ENERGY CONSUMPTION
Green roofs can reduce energy consumption up to 30% . Each building is different and buildings with large roofs can save the most energy by installing a green roof. Javits Center, which has the largest green roof in New York City of 7 acres, has saved three million dollars in energy reduction because of their green roof. Green roofs are most effective at reducing energy consumption in the summer because they cool the air through evapotranspiration. Green roofs can reduce air conditioning demand up to 75% during the summer. Green roofs increase the efficacy of HVAC units. When in cooling mode, HVAC equipment must pre–cool outside air to get it to the required temperature. If the air on the roof is made cooler by a green roof, this process is easier and uses less energy. Therefore, lower air temperatures on the roof improve the efficiency of heat–rejecting rooftop HVAC equipment because it is operating at a lower ambient temperature. Green roofs also increase the efficacy of solar panels.
4. MITIGATING URBAN HEAT ISLAND
Cities are often several degrees warmer than surrounding rural and suburban areas. Cities trap heat because they are built from concrete and contain many dark surfaces. Cities lack sufficient vegetation to shade surfaces and create cooler air through evapotranspiration. This increase of heat also worsens air quality. Black tar rooftops are some of the hottest places in cities during the summer. During a 90 degree (F) day black tar roofs are around 190 degrees (F). Green roofs, by contrast, are typically less than the ambient temperature. Green roofs not only reduce the temperature of a building, they have the ability to reduce the entire city’s temperature if constructed on a large scale.
5. NOISE REDUCTION
Noise pollution is particularly severe in cities. The World Health Organisation (WHO) has described noise pollution as an underestimated threat that can cause a number of health problems. Green roofs serve as a noise insulation barrier. They have a dampening quality that reduce sound transmission into the building. Sound waves are both absorbed, reflected and deflected by a green roof. The growing medium blocks lower sound frequencies and the plants tend to block higher frequencies. A green roof with a 12 cm substrate layer can reduce sound by 40dB and one of 20 cm by 46-50dB.
6. ROOF LONGEVITY
Green roofs protect the waterproofing of a building from UV Rays and thermal shock. Uninsulated roofing is exposed to Ultra Violet rays everyday that cause the waterproofing system to degrade. Thermal shock occurs when changes in temperature happen so quickly that it stresses the roofing. Rapid expansion or contraction can lead to severe damage and is one of the leading causes of leaks in waterproofing. Green roofs reduce thermal fluctuations keeping temperatures on the surface of the roof stable. This can extend the service life of the waterproofing system by as much as 50% saving property owners from costly repairs and replacement and reducing environmental impacts.
7. NATURAL HABITAT
Green roofs can function as natural habitat corridors, linking fragmented habitats and facilitating wildlife movement and dispersal, especially for migratory birds and butterflies. New York City can provide vital habitat for migratory species because it is an stopover location on The Great American Flyway. Green roofs can provide habitat for declining and endangered species and are an essential tool in species conservation.
8. OPEN GREEN SPACE
Green roofs can serve as an amenity space for residential or commercial tenants as well as for the community. Due to population density, NYC still has fewer acres of green space per person than almost any other major city in the U.S. Because real estate on the ground is so rare and valuable, few spaces can realistically be converted to parks, where as rooftops are a underutilized real estate in NYC offering 40,000 acres of empty space.
9. JOBS
Green roofs can be labor intensive and often require large teams. The green roof industry can provide jobs during installation as well as for long term maintenance services. Green roofs expose workers to a wide range of skills and experience ranging from construction to horticulture.
10. EDUCATION
Green roofs can serve as outdoor classrooms for students learning about green infrastructure, biology, science, urban design, and many other topics. More and more schools are looking to green roofs to expand their curriculum. An excellent example of this is PS 41 in New York City and the curriculum that has been developed from it.
11. PROPERTY VALUE
Green roofs create a more attractive building and a better tenant experience. Building owners are often able to get increased rents after installing a green roof. Green roofs also increase marketability and earn the property owner respect for investing in something that helps the environment and the community. Green roofs can earn a building owner up to 14 LEED Points.
