An intensive green roof on a local restaurant in Lansing




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What are green roofs?




An intensive green roof on a local restaurant in Lansing.
Green roofs, also called 'vegetative’, ‘living’, or ‘eco-roofs’, are living plants installed on top of conventional roofs. There are two types of green roof designs, extensive and intensive, which are discussed below. Properly designed, all green roofs are stable, living ecosystems that replicate many of the processes found in nature. A green roof can keep buildings cooler, save energy, extend the useful life of the roof, and add beauty and useable space. The many ecological and aesthetic advantages to having a green roof include:


  • Improving water quality-studies have shown that green roofs are highly effective at managing stormwater discharge from a roof, thereby protecting sensitive watersheds and potentially reducing costs of drainage basins and other stormwater management structures. Green roofs can detain and use 50 to 75 percent of a typical 1-inch (2.5cm) rainfall event.

  • Mitigating urban heat-island effects- green roofs lower rooftop temperatures from 130 degrees Fahrenheit or greater to approximately 75 F during a summer day. Less heat is radiated to the surrounding environment, helping to reduce the urban heat island effect.

  • Cleaning the air- Smog forming chemicals such as oxides of nitrogen and sulfur, as well as carbon dioxide are taken up directly by plants, lowering their concentrations in the air.

  • Extending the service life of the roofGreen roofs help to protect roofing membranes from extreme temperature fluctuations, the negative impact of ultraviolet radiation, and accidental damage from pedestrian traffic. European evidence indicates that green roofs will easily double the life span of a conventional roof, and thus decrease the need for re-roofing and the amount of waste material bound for the landfills.

  • Conserving energy- The cooling and shading properties of a green roof can significantly limit the heat flow into a building, thus lowering the load placed on air conditioning equipment and reducing energy consumption.

  • Reducing sound reflection and transmission- green roofs can reduce the levels of indoor sound by as much as 40 decibels, making for a healthier work or living environment. For comparison, a 30-decibel reduction is equivalent to the difference between the sound of a lawnmower (90 dB) and that of a normal conversation (60 dB).

  • Creating wildlife habitat- Green roofs installed on schools or universities also have the ability to offer students a unique, living laboratory in which various research projects and education can be conducted. Primary and secondary schools could also use an accessible green roof for horticulture experiments, biodiversity studies, or habitat creation.



  • Using recycled materials- Many of the materials used in green roof construction are manufactured from recycled building materials, plastics and rubber reducing landfill disposal.

Precursors to the modern green roof, such as sod roofs, have been used in many cultures for centuries. The modern green roof, which supports a natural ecosystem with advanced materials and technology, has been developed in Europe — primarily in Germany — over the last 35 years. As a response to serious regional ecological challenges, European government incentives have encouraged careful research and a flourishing green roof industry.


Green roof applications are appropriate for residential, farm, industrial, and office buildings.  They provide the greatest benefit in urban areas and in large industrial or commercial sites where impervious surfaces dominate. Depending on latitude, expected snow and rain load and building construction, additional reinforcement may or may not be necessary.  Typically, a green roof consists of a thin (2 – 3 inches) layer of soil and a drainage layer, applied directly to a roofing membrane.  For sloped roofs, baffles may be necessary to retain the soil.  Green roof plants are typically short perennials and succulents, including such varieties of Sedum or Delosperma.  These plants will quickly cover the soil and prevent erosion, retain rainwater, and provide insulation and respirative cooling.

Green roofs: An Ecological Balance. (Courtesy of Albrect Duerr)
There are the two basic types of green roofs, extensive or intensive, and are differentiated mainly by the cost, depth of growing medium and the choice of plants.
Extensive green roofs are characterized by the special growing medium which is a combination of light weight organic and inorganic materials. The growth media will vary between 2-6" in depth with a low weight increase of between 16-35 lbs/sf when fully saturated. Due to the shallowness of the growing medium and many roofs, plants must be low and hardy, typically alpine, dry land, or succulent plants. Typically the plants are watered and fertilized only until they are established, and after the first year, maintenance consists of two visits a year for weeding of invasive species, safety and membrane inspections.
On the other hand, Intensive green roofs have growth media depth somewhere between 8-24", with a higher saturated weight increase of between 60-200 lbs/sf. In having an increased soil depth, the plants can be more diverse and utilize trees, shrubs and other landscaping aspects. This allows for the development of a more complex ecosystem. Requirements for maintenance - especially watering - are more demanding and ongoing, and irrigation systems are usually specified. Structural and horticultural consultation and an experienced installer are recommended.


View of extensive green roof on the new assembly plant at Ford Motor Company, Dearborn during July 2003



In addition to being intensive or extensive, green roofs can also be built-in-place or modular systems. Most conventional green roof systems utilize a series of components that must be installed in layers on a roof surface. These have been referred to as built-in-place green roofs. Their primary drawbacks include complicated installation logistics, excess weight, and lengthy installation schedules. The number and types of materials that must be mobilized to the roof complicate the installation of built-in-place systems. These materials need to be placed sequentially and plants must be installed at the correct times and tended to ensure growth. Unless larger, more expensive nursery stock is used, the green roof installation may require one to two growing seasons before becoming “green”. The layers of components used in a built-in-place green roof system tend to be heavy (approximately 40 to 100 lbs/ft2). Retrofitting an existing roof may not be feasible if the structural capacity of the roof is not adequate. Supplemental irrigation systems can be problematic and must be designed for site-specific requirements. Repair and maintenance of the underlying roof can be cumbersome and costly since peeling back or replacing large sections of green roof may be required. For the reasons discussed above, built-in-place green roofs can be more complicated to install and remove than conventional roofs, discouraging their construction in the United States.

As a result, modular green roof technologies are rapidly gaining popularity. Modular systems retain all the benefits of the green roof while addressing the limitations of a built-in-place system.

The most notable benefits of using a modular approach to green roof construction are simplicity and flexibility. As compared to the built-in-place green roofs, modular systems are extremely lightweight, approximately 15 to 40 lbs/ft2 when wet. Pre-planted modules are commercially available in various sizes that are easily installed in a wide array of configurations. Plants are established and mature in the module prior to placement on the roof. The plantings are chosen to be wind and drought resistant and modules can be rotated seasonally if desired. The installation of the modular green roof can be completed in a matter of days or weeks and modules can be installed at nearly any time during the year because plants are pre-established. This design flexibility and installation efficiency help to further lower the cost of a modular green roof. It also allows an owner to modify the layout or add other modular features such as walkways, benches, etc. at any time in the future. Overall, plant survivorship is improved and the owner is provided with a green roof that has a very high degree of customization.

Since a green roof is made up of many components, it’s important to consider the complete system of all the roofing components as well as environmental factors. So before you start to build your green roof there are many complex, interactive factors that a green roof design engineer takes into account, balancing many considerations for optimal performance, including:


•  Climate, especially temperature and rainfall patterns

•  Strength of the supporting structure

•  Size, slope, height, and directional orientation of the roof

•  Type of underlying waterproofing

•  Drainage elements, such as drains, scuppers, and drainage conduits

•  Accessibility and intended use

•  Visibility, fit with architecture, and owner's aesthetic preferences

•  Fit with other “green” systems, such as solar panels

•  Costs of materials and labor

 

So as you can see there are many great reasons to grow a green roof. So with a little research and innovation you can join the elite of flourishing green roof industries:



  • Mallet Creek District Library, Ann Arbor MI

  • Ford Plant -Worlds largest green roof, Dearborn, MI

  • Chicago City Hall, Chicago, IL

  • Chicago Green roofs Map

  • Michigan State University, East Lansing, MI

  • Carrabbas Italian Grill, Lansing, MI

  • Helmus Building, Bazzani Hdqtrs, Grand Rapids, MI


Finnegan and Cooper pose by their green roofed doghouse

A listing of the known green roof projects in Michigan is available at:



www.michigan.gov/documents/deq/deq-ess-p2-green-greenroofs_186786_7.doc


References

(The above reference was developed by Nicole Vasilnek.)



For more information on green roofs visit the sites below on the “Green Roof Resource List”. To add or revise the list, contact the MDEQ at 517-335-6250 or fieldsm@michigan.gov .


Green Roof

Resources

Green Roof Awards for excellence

www.greenroofs.net/index.php?option=com_content&task=view&id=52&Itemid=67

Design Guidelines for Green Roofs -OAA

www.cmhc.ca/en/inpr/bude/himu/coedar/loader.cfm?url=/commonspot/security/getfile.cfm&PageID=70146

Eco Roofs

http://ecoroofsystems.com/grnRoof.html (no www)

EPA - Green Roofs & Heat Islands

www.epa.gov/heatisland/strategies/greenroofs.html

Green Roof.Com

www.greenroofs.com/

Green Roof - examples

www.greenroofs.com/projects/ (incomplete Michigan list)

Green Roofs – Healthy Cities

www.greenroofs.org

Green Roof Companies

www.greenroofplants.com/green_roof_links.htm

www.greenroofs.com

MSU Green Roof Research

www.hrt.msu.edu/greenroof/

NRDC Document “Out of the Gutter”

www.nrdc.org/water/pollution/gutter/gutterinx.asp

Roof Gardens: Design& Construction

www.oikos.com/store/cart.php?m=product_detail&p=77

Roofscapes

www.roofmeadow.com/

Smart Communities Network

www.smartcommunities.ncat.org

Xeroflora (used by Ford Rouge)

www.xeroflora.com

Example Roofs

Michigan green roofs

www.michigan.gov/documents/deq/deq-ess-p2-green-greenroofs_186786_7.doc

Chicago City Hall

http://chicagowildernessmag.org/issues/summer2004/greenroof.html

Chicago –map of all green roofs & FAQ

www.artic.edu/webspaces/greeninitiatives/greenroofs/main_map.htm

Ford Plant -Worlds largest green roof, Dearborn, MI

www.greenroofs.org/index.php?option=com_content&task=view&id=290&Itemid=50

Kresge Foundation

www.kresge.org/content/displaycontent.aspx?CID=8

Other Relevant Resource Lists

Also check out the resource lists on: Green Building; Building Material Recycling; Energy; Landscaping; Pollution Prevention; Recycling; and Sustainability.

Listing of these websites does not imply any endorsement by MDEQ. 06/08

Want to add resources to a list? Contact Maggie Fields, MDEQ, fieldsm@michigan.gov 517-335-6250




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