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Green Roofs

Green Roofs

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Green Roofs

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  1. Green Roofs • by Walter Tersch April 27, 2007

  2. Preview of presentation: • What is a green roof? • Two types of green roofs • Overview of Benefits, Construction, and plants • Pro’s and Con’s • Three case studies • Local incentives • Conclusion

  3. “Rooftop gardening is an attractive and energy-saving alternative to a conventional rooftop” Green Roof basics -Chicago’s Mayor Richard M. Daley • “Vegetation and soil or a growing medium planted over a waterproofing membrane” -U.S. EPA

  4. Two types of Green Roofs • (1) “Extensive” is also known as a green roof system or living roof. • Shallower 1”-5” growing material and hardy plants that require minimal maintenance; lighter; often accessible only for maintenance Chicago Department of Environment’s “Guide to Rooftop Gardening from the City of Chicago”

  5. Two types of Green Roofs • (2) “Intensive” is also known as a rooftop garden • Deeper 12+” growing material, more intricate or delicate plantings, and more maintenance such as irrigation and pruning required;heavier but generally accessible to people, like a ground garden • Requires two exits, barriers at roof’s edge, raised smokestacks, and a structural capacity load calculation that accounts for people. Note: Container gardens are cheapest and easiest type of “plants on roof” to maintain, but do not insulate or reduce stormwater runoff and are not considered green roofs Chicago Department of Environment’s “Guide to Rooftop Gardening from the City of Chicago”

  6. Overview of benefits • Reduce urban heat island effect • Improve air quality • Extend useful life of roof • Add beauty and usable space • Reduce stormwater runoff • Enhance energy efficiency of buildings, helping move towards energy independence

  7. Basic Construction • Ford Motor company’s 3-inch thick system: • Sedum plants and growing material • Fleece mat • Drainage Layer • Root-resistant Membrane • Green roofs originated in Europe, where sod has been a roofing material for hundreds of years. • Urban areas in Germany began adding GR’s more than 30 years ago; now one of every 10 flat roofs is green.

  8. Sedum • Most popular green roof plant • Virtually maintenance-free • A hardy flowering, creeping succulent that stores water in its leaves • Found throughout the Northern Hemisphere; also known as Stonecrop • Grows less than 6 inches tall and spreads horizontally, crowding out weeds; traps dust and consumes CO2 Sources: and

  9. Pro’s and Con’s

  10. Reduce urban heat island • On hot summer days, a green roof can be up to 90 degrees F cooler than a traditional dark rooftop surface according to the U.S. EPA • Plants cool surrounding air through evapotranspiration, the release of water into the surrounding air • Dark surfaces absorb sun’s energy and radiate heat long after sunset • Lighter colored surfaces reflect more light • Green roofs increase a city’s cooler shaded and reflective areas.

  11. Improve air quality • Direct: plants use excess carbon dioxide to produce oxygen • Indirect: air conditioners do not need to work as hard to keep building cool in summer. “Peaker” power plants need to activate less frequently in the summer, thus causing less air pollution (and lower energy prices) • Also, higher temperatures create more smog because pollution is magnified when chemicals in the air react with heat and sunlight. • Ground-level ozone is a components of smog dangerous to human health; it irritates the eyes, aggravates asthma, and causes permanent lung damage. Chicago Department of Environment’s “Guide to Rooftop Gardening from the City of Chicago”

  12. Extend useful life of roof • Protect the “hard” roof from exposure to the weather, the sun’s ultraviolet radiation and extreme daily temperature fluctuations. (U.S. EPA) • It is estimated that a green roof will double or even triple the life of a roof membrane (Buildings magazine, Dec. 2004: “Green Roofs” by Eric Horstman) • Reduced stresses on roofing typically prolong usable life by 20 years. Costs for rehabilitatition or replacement of roof can be delayed. (Green • Lifetime cost of green roof is comparable to cost of conventional flat roofs. (Green

  13. Add beauty and usable space • Provide habitat for birds and insects • Protect biodiversity • Improve urban quality of life • Reduce noise transfer from outdoors “by up to 25% for extensive roofs and more for intensive.” (Green

  14. Reduce stormwater runoff • Green roofs absorb rainfall and reduce urban runoff that would otherwise collect pollutants and empty into sewers for costly treatment • 3”-5” of growing medium absorbs 75% of rain events of 1/2” or less • Filter pollution from rainwater; root systems’ bacteria and fungi utilize natural filtering processes of bioremediation and phytoremediation to break down and detoxify nitrogen and phosphorus

  15. Enhanced energy efficiency • Less wasted energy = more energy independence • Can reduce a single-story building’s cooling costs by 20 to 30 percent(Buildings magazine, Dec. 2004: “Green Roofs” by Eric Horstman) • A 3 to 7 degree temperature drop translates to a 10% reduction in air conditioning requirements. ( • Weston Design Consultants’ study for the city of chicago estimated that it $100M could be saved annually with the greening of all the city’s rooftops. • “Peak demand would be cut by 720 megawatts -- the equivalent of several coal-fired generating stations or one small nuclear power plant.” (

  16. Drawbacks and Limitations • As a general rule of thumb, green roof systems cost 50% more than a conventional roof • U.S. EPA: Green Roofs start at $8/ sq. ft., including materials, preparation work and installation, whereas traditional roof starts at $1.25/ sq. ft. • Not all roofs can support the weight of green roofs (additional 12 to 150 lbs. per sq. foot) Chicago Department of Environment’s “Guide to Rooftop Gardening from the City of Chicago”

  17. Case Studies • Schwab Rehabilitation Hospital (intensive “roof garden”) • Ford Motor Company’s Rouge Center (extensive “living roof”) • Chicago City Hall (combination intensive/ extensive test garden)

  18. Schwab Rehab Hospital • 82-bed rehabilitation hospital located on Chicago’s West Side • 10,000 square foot therapeutic rooftop garden added in 2003 • Funded with $400,000 grant from City of Chicago’s Heat Island Reduction Initiative and $80,000 from private donors Healthcare Design, March 2006: “Urban Oasis” by Michael Wehner

  19. Schwab Rehab Hospital • Intensive roof garden; energy savings unknown • Built with structure for a 4th story

  20. Schwab Rehab Hospital • Waterfall feeds 50-foot pebble-lined stream; benefits patients • 50 midwestern savanna plant species selected; many drought-resistant or full sun.

  21. Schwab Rehab Hospital • Organic gardening techniques eliminate need for chemical fertilizer; composting reduces yard waste by over 90% • Volunteer master gardeners and recreational therapists maintain it

  22. Ford’s Rouge Center • In 2004, completed installation of the world’s largest “living roof” -- a 10.4 acre field of sedum on the truck plant’s final assembly building • Installed in pieces like sod • Ford’s oldest manufacturing facility. Constructed in 1917, has built everything from Model A’s to Mustangs to F-150’s. • At height, complex was 1.5 miles long and 1 mile wide and employed over 100,000 workers onsite

  23. Ford’s Rouge Center • Ford’s vertically oriented “ore to assembly” processes left their mark on the environment • In 2000, they launched their $2 billion Rouge Heritage Project. • The new roof stores rainwater and will save Ford money in the long run • Also has world’s largest porous parking lot to minimize stormwater runoff

  24. Ford’s Rouge Center • Experimental phytoremediation is being tested to treat soil containing harmful byproducts of steel manufacturing process • Microbes on special plants break down compounds into small fragments absorbed into roots • May prove to be a safe alternative to landfilling contaminated soil • Natural light is used on line • 20,000 honeybees live on plant grounds, aiding wildlife Source: “The Greening of the Rouge”, Ecology Center News, August 2003

  25. Chicago City Hall • Both extensive and intensive systems (3” to 24” thick soil) • G.R. was completed in 2001 after Mayor Daley saw many G.R.’s in Hamburg, Germany • 20,000 plants - 156 species incl. shrubs, vines and two trees • Hall built in 1911; structural capacity for a 12th story Source: Kevin Laberge, P.E., Chicago Dept. of Environment Environmental Engineer

  26. Chicago City Hall • First of its kind in Chicago; showcase for the whole U.S. • Funded through a settlement agreement between the City and ComEd • Radiating bands of species initially ested plants in different soil thicknesses, gradients, and drainage patterns; nature has taken its course

  27. Chicago City Hall • Drip irrigation used since 2002. • Two cisterns provide 10% of water • Existing 6 rooftop drains are utilized

  28. Chicago City Hall • Biodegradable mesh netting held initial plantings in place; cable anchors hold trees • Studies indicate that ambient air temperature is up to 78 degrees cooler than the air temperature above the black tar roof on Cook County half of the building Photo credits: Mark Farina, Chicago Department of Environment

  29. Chicago City Hall • Two beehives produce over 150 lbs. of honey per year, which is sold at Chicago Cultural Center • Estimated heating and cooling savings of $5,500 annually; city lacks ability to track actual savings Photo credits: Mark Farina, Chicago Department of Environment Sources:; Kevin Laberge, P.E., Chicago Dept. of Environment, Environmental Engineer

  30. Local Incentives • City of Chicago: • The City awarded 40 $5,000 “green building and design” grants to residential and small businesses in 2006. • There are now more than 80 green roofs established or underway in Chicago, on public and private buildings. News Star, 4/11/07: “Going Green” by Karen Shoffner

  31. Conclusion • Most green roofs should be able to use the existing rooftop drainage system with only minor modifications • Due to benefits including energy savings, enhanced roof life, stormwater reduction, beautification, and air quality improvement, green roofs make sense for all new roofs. • Since 2001, City of Chicago requires all new roofs to be either reflective-coated or green roofs