The Foundation for a Green Future, Inc. ("Foundation") is dedicated to ensuring a green future for our planet through education, training, advocacy and research. It is founded upon the principle that our every endeavor will be to teach and model sustainability in a way that will help restore a more natural balance to our living spaces, particularly our urban environment. Green roofs and living walls are therefore a primary focus of the Foundation. At Boston GreenFest this year, we will provide examples of green roofs and living walls and make the plaza as green as possible.
What is a green roof?
The term green roof refers to a roof that is partially or completely covered with vegetation, particularly one in which special membranes and other layers protect the rooftop and hold the plants and growing media in place.
Green roofs date back at least to 600 BC, to the Hanging Gardens of Babylonia, one of the world's seven wonders. In the 1930s in the United States and elsewhere, architects experimented with landscapes on buildings, like the Rockefeller Center in New York City. Germany has been perfecting modern day thin, veneer green roof technology since the early 1970s when the first lightweight green roof systems were developed and marketed.
Extensive green roof systems from Germany were introduced in the USA in the late 1980s. In temperate areas, extensive green roofs have been successfully developed that are 3-5 inches in depth, do not require irrigation, and weigh around 18-30 pounds per square foot. They rely on various perennial species of Sedum, which are hardy flowering succulent plants.
Due to their light weight, green roof systems can be incorporated into new construction or retrofitted onto existing buildings. The roofs can be flat or pitched.
What is a living wall?
Living walls are divided into two main categories: green faÇades and living walls. Green faÇades are made up of climbing plants either growing directly on a wall or specially designed supporting structures. The plant shoot system grows up the side of the building while being rooted in the ground. With a living wall the modular panels are often made of stainless steel containers, geotextiles, irrigation systems, a growing medium and vegetation. There are also "edible walls" that are planted with vegetables or herbs.
Living walls can be installed on the interior or exterior of a building. Indoors they improve air quality, filtering the air, absorbing CO2 and providing oxygen. Outdoors, they function similarly, with the additional benefit of cooling the building by as much as 20%.
Why do they matter?
Given the present trends of global warming and the contribution of urban heat island effect to this problem, green roofs are a very important mitigating element of the green building industry.
On a conventional roof, temperatures can soar to 150°-200°F, whereas a green roof remains cool at 77°-90°F. This can have a huge impact on reducing the urban heat island effect, increasing overall energy efficiency and eventually eliminating peak demand. Green roofs are particularly useful for stormwater management and reducing polluting runoff.
They absorb CO2 and release oxygen. Research performed at the University of Michigan shows that one acre of green roofs (40,000 square feet) absorb approximately two tons of CO2!
Green roofs can make a difference to our buildings, our energy use, our oceans, our health, our biodiversity, our economy, our water, and our overall quality of life. Since our cities are cement ovens with insufficient green coverage, green roofs can help bring the world's temperature down while creating lots of local green jobs.
Greening the Plaza
Green roofs can be elevated on the top of a building, or they can be at "grade level" or "street level." Once it is greened, Boston City Hall Plaza is a perfect example of a grade level green roof, since it sits above the train station. We have a variety of companies providing ways for us to green City Hall Plaza: