Although popular in Europe, green roofs are a relatively new technology in the United States. As of 2004, there are ten green roof design and installation firms in North America. Using cutting-edge research, these companies have developed two green roof systems: modular and built-in place to fit the needs of the urban community.
Modular Systems
Modular green roof technologies have become popular in the United States, due to their ease of installation, simple design, and flexibility. This design is also inexpensive and takes less time to install compared to other green roof technologies. In the U.S., two companies provide modular technology:
At Great Lakes WATER Institute, the Green Grid™ System fit the particular needs of our facility.
Key characteristics of modular systems
- Typically, utilized for extensive green roofs.
- Soil depths are typically 1 to 6 inches.
- Lightest load of all green roof systems: 15 to 50 punds per square foot.
- The placement of the modules can be rotated seasonally, moved for maintenance, or repair at any time.
- Growing medium usually contains sand, gravel, peat, organic matter, crushed brick, L.E.C.A. (Lightweight expanded clay aggregate) and some soil.
- The green roof can be installed any time of the year because the vegetation is commercially available, pre-planted, and established before installation occurs.
- The plants are prepared ahead of time which provides the plants with a higher rate of survival and overall success of the green roof.
How it works
The installation process usually takes several days to a couple of weeks depending on the size of the green roof. Plastic interlocking containers are filled with a drainage system, growing medium, and vegetation (Dunnett and Kingsbury, 2004) prior to installation decreasing the time needed to install the green roof. The plant selection is limited to drought-resistant and weather tolerant plants such as sedums, grasses, and some wildflowers because they require less maintenance and cultivation. When the green roof is completed, the building owner must water and weed on a regular basis for the first year until the plants are established to ensure proper growth and success.
Built-In Place Systems
Urban Ecology Center, Milwaukee, Wisconsin |
Built-in place green roofs were developed in Europe and still utilized today. This green roof technology is more complex, permanent, and expensive than modular systems due to the time and costs needed for installation. The majority of green roof companies install this type of technology in North America. The following companies install built-in place green roof systems:
- American Hydrotech, Inc.
located nationwide
- Barrett Company
Millington, NJ
- Sarnafil, Inc.
located nationwide
- W.P. Hichman Systems, Inc.
Solon, OH
- American Wick Drain Corporation
Monroe, NC
- The Garland Company
Cleveland, OH
- Roofscapes, Inc.
Philadelphia, PA
- Soprema, Inc.
located nationwide
Key characteristics of built-in systems
- Typically, utilized for intensive or semi-intensive green roofs (soil depths of 4 to 8 inches).
- Designs must be planned accurately and entirely finished before construction begins because the green roof installation can not be changed easily.
- The weight load is heavier than a modular system. A typical load of this green roof is 40 to 100 pounds per square foot and may require structural support for the building (Markham and Walles).
- Growing medium is usually soil-based.
- More diverse plant selections and public accessibility with a built-in place system.
How it works
Green roof construction usually takes months or sometimes longer because materials need to be placed in a particular sequence. Layers of the green roof include, vegetation, growing medium, drainage, irrigation system, waterproofing, insulation, and roof access are installed one by one on the actual roof membrane. Vegetation may need one or two growing seasons to become established in pots before they are planted in the green roof substrate, depending on the size of the green roof and the plants used. The maintenance of a built-in place system requires regular watering, weeding, and cultivation through-out the life of the green roof.
Green Roof Components
Cross section of typical green roof system
(Source: http://www.greenroofs.org/index.php?page=aboutgreen)
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