Although roof gardens may seem like a more recent phenomenon in many locations, these building features have actually been in existence since the fourth millennium. While 21st century efforts toward environmental protection and green space cultivation have expanded the use of roof gardens, particularly in urban areas, it is not a new development.
Many terms used for roof gardens: green roofs, vegetated roofs, and living roofs. But what exactly is a roof garden? By definition, it is a contained green space that sits either above, below, or at grade on top of an existing manmade structure.
There is a reason that roof gardens are not a new phenomenon, and that is the plethora of benefits that these provide. These exterior areas help to facilitate stormwater management, increase a building’s amenity space, reduce the urban heat island effect, extend a rooftop’s service life, and reduce required building maintenance.
EASING STORMWATER MANAGEMENT
Stormwater management is a significant challenge in many communities. According to the U.S. Environmental Protection Agency, there are 772 communities across the U.S. that operate with combined sewer systems. This means that rainwater runoff, domestic sewage, and industrial wastewater are collected in the same pipes.
While most modern communities have separate pipe systems to collect and divert stormwater and sewage, many older American cities were built with these combined systems. In these locations, during periods of heavy rainfall or snowmelt the water entering the sewer system often exceeds the capacity of local wastewater treatment facilities. When this occurs, these systems overflow and discharge excess wastewater directly into nearby streams, rivers, and other bodies of water. For obvious reasons, this method of stormwater management is less than ideal, and can negatively impact the surrounding environment and community.
This is where roof gardens can help to ease stormwater management challenges. With the combined sewer systems described above, stormwater is not “managed” but merely flows through the sewer system, overflowing system capacity. Roof gardens help to prevent this overflow by detaining and retaining the rainwater, thus filtering and reducing stormwater runoff. The deeper the roof garden, the more stormwater retention that is possible; studies have shown that a 4″ extensive sedum roof is able to capture 60-75% of annual rainfall in temperate climates.
For the Rice Fruit Company in Gardners, PA, a roof garden provided a solution for the construction of a new facility. Since 1913, this company has distributed fresh fruit throughout the U.S., and as the largest apple packing facility in the eastern half of the country Rice has a reputation for high standards.
When the company’s owners decided to expand operations and construct a new cold storage facility at its Gardners site, they wanted to make the building environmentally friendly and unobtrusive, so it would blend into the surrounding countryside. A roof garden seemed like the perfect solution.
While the aesthetic of the new facility was important, there was another significant benefit to Rice including a new roof garden. Pennsylvania building codes required that a retaining pond be installed with most commercial building construction in order to manage stormwater runoff and prevent flooding. With the new construction, there would be no space on the property for a retaining pond. By installing a roof garden system, however, Rice was able to meet building code requirements for stormwater management without the additional retaining pond.