Green Roofs Costs Lake Timothy Final Presentation

8/14/2019 Green Roofs Costs Lake Timothy Final Presentation

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Does it Pay to go Green? A Cost-Benefit

Analysis of Green Roofs in the NYC Metropolitan Area

By Tim Lake

Earth & Environmental ScienceDepartment, General Studies @Columbia UniversityMentor: Cynthia Rosenzweig,

Goddard Inst. for Space Studies NASAAdvisor: Martin Stute

Chicago City Hall Urban Heat Island Initiative project(Source: Roofscapes, Inc. )


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Principal Green Roof TechnologyComponents


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Types of Green RoofsEXTENSIVE GREEN ROOF

Thin growing medium; little or no irrigation; stressfulconditions for plants; low

plant diversity.

Disadvantages:Less energy efficiency andstorm water Retention benefits.More limited choice of plants.

Usually no access for recreation or other uses.Unattractive to some,especially in winter.

INTENSIVE GREEN ROOF

Deep soil; irrigation system;more favorable conditions for

plants; high plant diversity;often accessible.

Disadvantages:Greater weight loading onroof.

Need for irrigation anddrainage systems

requiring energy, water,materials.Higher capital & maintenancecosts.More complex systems andexpertise.


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General Construction Costs of anInaccessible Extensive Green Roof system

Design Consideration and Site Review: 5%-10% of totalroof cost

Re-roofing with Root repellant membrane: $8-$12 per sq.ft.Green Roof System: $5-$10 per sq.ft.Plants: $1-$3 per sq.ft.Installation / Labor: $3-$8 per sq.ft.Maintenance: $1.25-$2.00 per sq.ft.Irrigation: $2-$4 per sq.ft.Generic Average Total Cost: $15-$22 per sq. ft.


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Green Roof Manufacturers

Soprema: $12-18/sf Barrett: $15-20/sf Siplast: $15-16/sf Weston: $10-12/sf Roofscapes: $14-20/sf

Building Logics: $12/sf Hydrotech: $10-18/sf Sarnafil: $15-20/sf


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Public Benefits of Green RoofsUrban Heat Island Effect - GHG ReductionsStormwater Retention - Decreased Combined SewageOverflowAir Quality - Decrease in Airborne Particulate Matter Creation of Habitat - BiodiversityGeneral Public Benefits i.e. Aesthetic Value

A office/school complex with a green roof


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Private Benefits of Green RoofsEnergy Savings - Reduction in Cooling CostsRoof Membrane Protection & Life ProtectionSound Insulation & Reduction in SoundTransmissionGeneral Private Benefits i.e. Aesthetic Value


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Thesis StatementThis study will involve a cost-benefit analysis, for both the private and public sectors, of greening 5% of flat rooftops inthe NYC metropolitan area with extensive green roofs in afive-year period. The cost/benefit analysis will outline themajor costs of manufacturing green roofs for the NYC areaand the potential benefits of the implementation of greenroofs, which will reduce the short-term manufacturing costs

and create long-term environmental benefits.


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Approach/MethodsI will look at a time period of 50yrs and the cost and

benefits per square footage of green roofs to bedeveloped.From this point, I will incorporate the costs and benefits

per square foot to the total amount of square footage inthe NYC area to be developed. I will then compare thesefigures to the cost and benefits of not developing greenroofs in the city.

I will use averages of various manufacturers costs and benefits.


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Approach/Methods Cont.

This study will involve some simplifications andassumptions due to the time constraint and lack of information available in some areas. The data will becollected from research of other studies conducted indifferent major metropolitan cities with similar climate as

NYC. This project will be limited, since there will be noreal data from NYC.

Vancouver City Library -Vancouver, Canada


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Preliminary Results: Private Benefits

1. Economic Benefits: reduced heating and coolingcosts/increased property valueEnvironment Canada found that a one-story building with a grassroof and 3.9 inches of growing medium could result in a 25%reduction in summer cooling needs . Chicagos City Hall, which has

a large green roof, is expected to save up to $5,000 a year in heatingand cooling costs due to the roof. Green roofs can increase propertyvalue by as much as 15%.

2. Protection of roof membraneA green roof can extend the lifespan of a roofing membrane by

protecting it from intense UV degradation and continued expansionand contraction due to fluctuating temperatures. Most roofs have to

be replaced every 15 to 20 years; some green roofs in Germanyhave lasted as long as 40 years without needing to be replaced.


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Preliminary Results: Private Benefits Cont.3. Sound InsulationA roof covered in soil and plants can be a great soundinsulator.4. Amenity and recreational space

Green roofs provide a beautiful, natural environment for recreation.5. Food Production

A well-planned green roof can support all the same plantsand herbs that can be found in a traditional garden. TheFairmount Waterfront Hotel in Vancouver grows herbsand vegetables on its green roof, saving its kitchen$30,000 a year in food costs.


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Preliminary Results: Public Benefits1. Reduction of the Urban Heat Island Effect:The term urban heat island effect refers to the difference intemperature between a city and its surrounding areas. This differencecan be up to 10 degrees. Plants cool their surrounding environmentsthrough natural evapotranspiration cycles. With more green roofs inthe city and less hard, nonporous blacktop, our cities can be cooleddown.2. Storm-water Retention:Storm-water creates serious urban water pollution problems. Greenroofs, which can retain up to 75% of a one-inch rainfall, alleviate

pressure on citys overburdened sewer systems. During heavy

rainstorms many cities combine their storm water with their household sewage waste due to the increased pressure on sewagetreatment plants. Thus, raw, untreated sewage is often releaseduntreated into city waterways.


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Preliminary Results: Public Benefits Cont.3. Improved Air Quality:Green roofs filter air by absorbing and converting carbon dioxide and

producing oxygen. Just 1.5 square meters of uncut grass producesenough oxygen in a year to supply one persons yearly oxygen intakeneeds. 1 m2 (10.76 ft2) of grass roof can remove between 0.2 kg of airborne particulates from the air every year .4. Energy Conservation: Citywide green roof implementation has the potential to reduce theambient air temperature in a city. Lower temperatures during summer months result in decreased demand for electricity.5. Habitat & BiodiversityIn Germany, research has shown that green roofs can supportanywhere from 10 to 40 different insect species and have even beenfound to harbor nesting bird species.


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Implications of ResearchThis cost-benefit analysis will be the first of itskind in the NYC area. If successful, this research

will show that the benefits of green roofs willsignificantly outweigh the costs.I believe this study will put some economicvalues (monetary values) on an incentive to green

roofs in a major metropolitan area, which will bemost beneficial in convincing governmentofficials and agencies to implement policies togreen this wonderful city.


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Implications of Research Cont.The cost-benefit analysis spreadsheet can begiven to private building owners as well asgovernment officials for use in developing

policies for green roof implementation across thecity.This will provide policy makers with scientificand cost-benefit analysis to determine therationale for and proper means of developing agreen roof infrastructure.

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Green Roofs Costs Lake Timothy Final Presentation