Nashville Civic Design Center
Green Roofs Case Study A green roof consists of vegetation, soil or a growing medium, planted over a waterproofing membrane. Root barriers, drainage and irrigation systems may be included as additional layers. Green roof technology typically utilizes some other forms of green technology, such as rooftop ponds, solar panels or photovoltaic modules. Colored green roofs or green shingles, as well as container gardens, where plants are maintained in pots, are not considered to be green roofs. Green roofs are also sometimes referred to as eco- vegetated or living roofs.
• Protect underlying roof material by eliminating exposure to the sun’s ultraviolet (UV) radiation and extreme daily temperature fluctuations. • Serve as living environments that provide habitats for birds and other small animals. • Offer an attractive alternative to conventional roofs • Reduce noise transfer from outdoors. • Insulate building from extreme temperatures Green roofs also reduce storm water run off by absorbing water in a manner, similar to a sponge. “Researches estimate that three to five inches of soil or growing medium absorbs 75% of rain events that are one-half inch or less.”1 The plants retain pollutants in their soil and release the water back into the atmosphere via condensation and transpiration. Types
http://www.epa.gov/hiri/strategies/greenroofs.html
Benefits Green roofs are used to: • “Provide amenity space for building occupants – in effect replacing a yard or patio. • Grow fruits, vegetables, and flowers. • Reduce heating and cooling loads on a building • Reduce the urban heat island effect.” • Reduce stormwater loads by holding large amounts of rainwater on site • Absorb air pollution, collect airborne particulates, and store carbon.
Green roofs can be classified into three different types: intensive, semi-intensive and extensive. The categorization results from the “depth of planting medium and the amount of maintenance they need.”2 The intensive type calls for reasonable depth of soil or conventional lawns. It is very labour and time intensive. Irrigation, fertilizing and other maintenance is required. Extensive green roofs are practically self-sustaining. They need minimal annual maintenance (weeding and fertilizer) and can be seeded on a very thin layer of soil. The semiintensive green roof requires some maintenance between the two other types. Another differentiation of green roofs is between pitched and flat roofs. Pitched roofs are more traditional and simply designed, “because the pitch of the roof reduces the risk of water penetrating through the roof structure, allowing the use of fewer waterproofing and drainage layers.”3 Disadvantages, Costs and Advantages Disadvantages of green roofs include added costs. Depending on the roof type, the structure of the building and including
Sources: 1
http://www.epa.gov/hiri/strategies/greenroofs.html
2 http://en.wikipedia.org/wiki?Green_roof 3
http://en.wikipedia.org/wiki/Green_roof
Nashville Civic Design Center • Green Roof Case Study • Nashville area Projects • www.civicdesigncenter.org
1