Green Roofs Amber Page 4/9/07 Rooftop of Chicago’s City Hall

Overview  What is a green roof?  History  Categories  Components  Benefits  Disadvantages  Cost  Examples

What is a green roof?  Layer of soil and vegetation that continuously covers a roof’s surface  Multi-beneficial structural component that helps alleviate the effects of urbanization on water quality  Green roofs do not include container gardens on roofs where plants are grown in pots

History  Ancient technology that has been used for thousands of years Hanging gardens of Babylon Viking houses

History  The modern use of green roofs is fairy recent Developed in Germany in the 1960s  Spread across Germany and Europe Currently, about 10% of German roofs are green  Becoming popular in cities such as Chicago, Portland, and Atlanta Chicago city hall one of the earliest examples in U.S.

Categories  Intensive Thick layer of soil Large plants and conventional lawns Labor-intensive to install Labor-intensive to maintain More aesthetically pleasing than extensive  Semi-Intensive  Extensive Thin layer of soil Self-sustaining Minimal maintenance Require less structural support than intensive roofs More cost effective than intensive

Categories Intensive green roof in Manhattan

Categories Intensive green roof on top of a hotel in British Columbia

Categories Extensive green roof on top of a museum in France

Categories Extensive green roof in Sugar Loaf, PA

Components

Components

Benefits-Storm Water Management  Utilizing the biological, physical, and chemical processes found in the plants and soil to naturally remove pollutants from the rainwater so they do not enter the storm drainage system Bioremediation and phytoremediation  Reduces runoff volume and discharge rate of water into the storm drainage system Buildings and parking lots replace large areas of vegetation that rainwater would normally seep into Green roofs absorb this water that would normally run off of roofs Can absorb 75% of the water during a rain storm of ½ inch or less  Increases temperature of runoff so less thermal shock occurs in drainage system

Benefits-Storm Water Management

Benefits- “Urban Heat Island” Effect  The “Urban Heat Island” effect is the difference in temperature between a city and the surrounding countryside  Traditional building surfaces absorb solar radiation and reflect it back as heat  Surfaces of conventional rooftops can be 90˚F warmer than the air temperature  In an urban area, temperatures of the city can be about 12˚F warmer than surrounding areas during the summer

Benefits- “Urban Heat Island” Effect  EPA estimates that air conditioning accounts for nearly 1/6 of energy generated per year Nearly $40 billion/yr nationwide  Reducing urban cities’ temperatures about 5.4˚F would save $6 billion/yr in energy costs nationwide

Benefits- “Urban Heat Island” Effect  Green roofs Forms a protective layer, shading the rooftop from UV radiation  Photosynthesis  Plants use energy from the sun to form carbohydrates Reduces roofs surface temperature through evapotranspiration  Loss of water through evaporation from soil and transpiration from plants’ leaves

Benefits- “Urban Heat Island” Effect

Benefits- “Urban Heat Island” Effect  Test green roof reduced average daily energy demand for space conditioning by 75% in summer

Benefits-Reduced Heating Costs  During winter, evapotranspiration nor photosynthesis can take place  Green roof does add a layer of thermal mass on top of roof  Air pockets in soil act as insulators  Surface textures of plants help reduce cooling from wind Reduces surface velocity of wind

Benefits-Reduced Heating Costs  Less effective at lowing heat transfer in winter than in summer  Only lowered heat loss by 26%

Benefits-Others  CO 2 Sequestering Take in CO 2 from air and release oxygen back into atmosphere  Removes Nitrogen Oxides (NO x ) from air Reduces smog by lowering air temperatures  Accounts from over 30% of air pollution  NO x reacts with volatile organic compounds  Accelerated at higher temperatures Negate acid rain effect  Removes other air pollutants Fixes particulates onto plant foliage Plants can reduce gaseous pollution by 90% by intake  Can also reduce air pollution by reducing energy needs Electricity demands in buildings can be reduced by nearly 45% Could translate into 10% reduction in carbon emissions

Benefits-Others  Lengthen life of roof by 2-3 times Lower temperature fluctuations Protection from UV radiation  Reduces noise from outside 8 inch layer of soil can reduce traffic noise by 46 decibels  Aesthetically pleasing Replaces yard or patio  Increases wildlife in area Sheltered from traffic, noise, predators, and human activities Migratory birds and butterflies benefit particularly Some green roofs have specifies of insects and birds that are otherwise extinct in area

Disadvantages  Need to strengthen structural supports before putting green roofs on existing buildings More demanding structural standards  Many existing buildings can not be retrofitted for green roof due to structural loads  Green roofs need to be adapted depending on climate of area Not one design that will work Most designs are currently for Europe  Harder to detect and fix leaks in roof once installed

Cost  Traditional roofs are about $1.25/sf  In U.S., green roofs start at about $8-15/sf Includes  Materials  Preparation  Installation Does not include  Future savings on air conditioning  Future savings on heating  Reduced storm water infrastructure  Increased life of roof  Decreased storm water permit fees and runoff treatments After taking into account everything, cost likely to be around that of a traditional roof Costs are continuously dropping due to increase in popularity  More contractors

Examples  Ford Motor Company’s River Rouge Plant, Dearborn, MI Extensive green roof One of the largest in the world 454,000 sf  Chicago’s City Hall One of the first green roofs in U.S.  Gap headquarters in San Bruno, CA  Moos Lake water-treatment plant, Switzerland One of the oldest green roofs in the world Built in 1914

Examples Village of Bour in the Faroe Islands

References   stormwater.net/greenroofs/greenroofs_home.htm stormwater.net/greenroofs/greenroofs_home.htm  l l     nt&task=view&id=26&Itemid=40 nt&task=view&id=26&Itemid=40  