2/29/2016
Balance is something all people desire in an ever demanding and changing world. At times, balance can seem unattainable, but the vast majority of the population succeeds by balancing work with family, finances with recreation, and sustainability with progress. Many environmentalists believe balance is too far out of reach; that humans cannot continue to press forward in the fields of technology and development without dire consequences to the environment. However, the balance of nature and progress is already being achieved and its effects are profound. Cities across the globe are striking this balance by incorporating rooftop gardens into their landscapes.
Rooftop gardens have numerous benefits for the environment and the people who enjoy them. Rooftop gardens also commonly known as green roofs, act as insulation; they absorb heat from the sun and cool the surrounding air via evapotranspiration which, in turn, lessens the need for air conditioning during the summer. Additionally, during winter the garden traps heat in, keeping the building warm. Green roof vegetation reduces air pollution, filters storm water pollution from rainfall, and diminishes carbon emissions through carbon sequestration. For the people who utilize rooftop gardens, they provide an unparalleled beauty juxtaposed with a concrete urban environment. Intensive rooftop gardens can also be used to grown fresh produce which provides further environmental and societal benefits.
Photo: Basic Structure of a rooftop garden. Credit: Hotel Verde
They consist of a layer of vegetation grown on a rooftop and provide shade, reduce temperatures, and help offset a person’s carbon footprint. There are 3 types of rooftop gardens including the extensive, semi-intensive, and intensive green roofs. Every rooftop garden follows the same basic structure. A waterproof membrane is placed down first to protect the existing roof, a root barrier is then placed followed by a drain mat, water retention fleece, growing medium, and vegetated layer.
Extensive green roofs are the simplest and least expensive option; they are best for roofs with small load bearing capacity and are characterized by their vegetation which consists of drought resistant plants, small grasses, perennials, and herbs. This type of green roof involves little maintenance and no permanent irrigation system. Extensive green roofs typically have a 1 inch drainage layer followed by a 2-4 inch deep growing medium with rudimentary soil mix.
Semi-intensive green roofs have a deeper substrate which allows tall grasses, shrubs, and herbaceous plants. This bio-diverse array of foliage also acts as a wildlife sanctuary. Semi-intensive green roofs have a 2.5-4 inch drainage layer followed by 6-9 inches of intensive soil mix3. This type of rooftop garden is more expensive to maintain because it requires a granular drainage system.
Intensive green roofs are the most sophisticated and can host bushes, trees, benches, and even small ponds. Intensive rooftop gardens consist of a 2-10 inch drainage layer and a 3-12 inch layer of intensive soil mix as growing media. Intensive rooftop gardens require a more advanced drainage plate for irrigation and can only be installed on roofs with a high load bearing capacity.
The sustainable trend of rooftop gardens is beginning to become common place. Chicago, New York, Seattle, and San Francisco are just a few major cities that are expanding their cityscapes with green alternatives. The Sacramento metro area is just beginning to use rooftop gardens and there are only a few places that currently have them, according to this article in the Sac Bee. http://www.sacbee.com/news/local/article2610539.html
In the future, hopefully the urban concrete jungle will be topped in a sea of green, but until that point the world can take comfort in the fact that balance is possible and continue to watch the sustainability and development progress together.
By Alyssa Harmon, guest blogger
1Green Landscaping and Vegetated Roof. (2012, May 14). Retrieved April 27, 2015, from http://hotelverde.co.za/blog/article/green-landscaping-and-vegetated-roof
2Extensive Green Roofs. (n.d.). Retrieved April 1, 2015, from http://www.greenrooftechnology.com/extensive-green-roof
3Semi Intensive Green Roofs. (n.d.). Retrieved April 1, 2015, from http://www.greenrooftechnology.com/semi-intensive-green-roof
4Intensive Green Roofs. (n.d.). Retrieved April 1, 2015, from http://www.greenrooftechnology.com/intensive-green-roof
5Green Roofs | Heat Island Effect | US EPA. (n.d.). Retrieved April 5, 2015, from http://www.epa.gov/heatisland/mitigation/greenroofs.htm
