Green Roofs Costs Lake Timothy Final Presentation

Does it Pay to go Green? A Cost-Benefit Analysis of Green Roofs in the NYC Metropolitan Area By Tim Lake Earth & Environmental Science Department, General Studies @ Columbia University Mentor: Cynthia Rosenzweig, Goddard Inst. for Space Studies NASA Advisor: Martin Stute Chicago City Hall Urban Heat Island Initiative project (Source: Roofscapes, Inc.)

Principal Green Roof Technology Components

Types of Green Roofs EXTENSIVE GREEN ROOF

INTENSIVE GREEN ROOF

Thin growing medium; little or no irrigation; stressful conditions for plants; low plant diversity. Disadvantages:  Less energy efficiency and storm water  Retention benefits.  More limited choice of plants.  Usually no access for recreation or other uses.  Unattractive to some, especially in winter.

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Deep soil; irrigation system; more favorable conditions for plants; high plant diversity; often accessible. Disadvantages:  Greater weight loading on roof.  Need for irrigation and drainage systems  requiring energy, water, materials.  Higher capital & maintenance costs.  More complex systems and expertise.

General Construction Costs of an Inaccessible Extensive Green Roof system        

Design Consideration and Site Review: 5%-10% of total roof 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.

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

Public Benefits of Green Roofs     

Urban Heat Island Effect - GHG Reductions Stormwater Retention - Decreased Combined Sewage Overflow Air Quality - Decrease in Airborne Particulate Matter Creation of Habitat - Biodiversity General Public Benefits i.e. Aesthetic Value A office/school complex with a green roof

Private Benefits of Green Roofs   

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Energy Savings - Reduction in Cooling Costs Roof Membrane Protection & Life Protection Sound Insulation & Reduction in Sound Transmission General Private Benefits i.e. Aesthetic Value

Thesis Statement This study will involve a cost-benefit analysis, for both the private and public sectors, of greening 5% of flat rooftops in the NYC metropolitan area with extensive green roofs in a five-year period. The cost/benefit analysis will outline the major costs of manufacturing green roofs for the NYC area and the potential benefits of the implementation of green roofs, which will reduce the short-term manufacturing costs and create long-term environmental benefits.

Approach/Methods 

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I will look at a time period of 50yrs and the cost and benefits per square footage of green roofs to be developed. From this point, I will incorporate the costs and benefits per square foot to the total amount of square footage in the NYC area to be developed. I will then compare these figures to the cost and benefits of not developing green roofs in the city. I will use averages of various manufacturers’ costs and benefits.

Approach/Methods Cont. This study will involve some simplifications and assumptions due to the time constraint and lack of information available in some areas. The data will be collected from research of other studies conducted in different major metropolitan cities with similar climate as NYC. This project will be limited, since there will be no real data from NYC. Vancouver City Library Vancouver, Canada 

Preliminary Results: Private Benefits 

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1. Economic Benefits: reduced heating and cooling costs/increased property value Environment Canada found that a one-story building with a grass roof and 3.9 inches of growing medium could result in a 25% reduction in summer cooling needs. Chicago’s City Hall, which has a large green roof, is expected to save up to $5,000 a year in heating and cooling costs due to the roof. Green roofs can increase property value by as much as 15%. 2. Protection of roof membrane A green roof can extend the lifespan of a roofing membrane by protecting it from intense UV degradation and continued expansion and contraction due to fluctuating temperatures. Most roofs have to be replaced every 15 to 20 years; some green roofs in Germany have lasted as long as 40 years without needing to be replaced.

Preliminary Results: Private Benefits Cont.  

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3. Sound Insulation A roof covered in soil and plants can be a great sound insulator. 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 plants and herbs that can be found in a traditional garden. The Fairmount Waterfront Hotel in Vancouver grows herbs and vegetables on its green roof, saving its kitchen $30,000 a year in food costs.

Preliminary Results: Public Benefits  

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1. Reduction of the Urban Heat Island Effect: The term urban heat island effect refers to the difference in temperature between a city and its surrounding areas. This difference can be up to 10 degrees. Plants cool their surrounding environments through natural evapotranspiration cycles. With more green roofs in the city and less hard, nonporous blacktop, our cities can be cooled down. 2. Storm-water Retention: Storm-water creates serious urban water pollution problems. Green roofs, which can retain up to 75% of a one-inch rainfall, alleviate pressure on city’s overburdened sewer systems. During heavy rainstorms many cities combine their storm water with their household sewage waste due to the increased pressure on sewage treatment plants. Thus, raw, untreated sewage is often released untreated into city waterways.

Preliminary Results: Public Benefits Cont.  

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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 produces enough oxygen in a year to supply one person’s yearly oxygen intake needs. 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 the ambient air temperature in a city. Lower temperatures during summer months result in decreased demand for electricity. 5. Habitat & Biodiversity In Germany, research has shown that green roofs can support anywhere from 10 to 40 different insect species and have even been found to harbor nesting bird species.

Implications of Research 

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This cost-benefit analysis will be the first of its kind in the NYC area. If successful, this research will show that the benefits of green roofs will significantly outweigh the costs. I believe this study will put some economic values (monetary values) on an incentive to green roofs in a major metropolitan area, which will be most beneficial in convincing government officials and agencies to implement policies to green this wonderful city.

Implications of Research Cont. 

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The cost-benefit analysis spreadsheet can be given to private building owners as well as government officials for use in developing policies for green roof implementation across the city. This will provide policy makers with scientific and cost-benefit analysis to determine the rationale for and proper means of developing a green roof infrastructure.