Figure 2: Energy cost and savings of a green roof Figure 1: Cost and savings of a green roof Life Cycle Assessment of a Green Roof Kate Dusinberre Pinkerton Academy, Derry, NH Results Approximately 40 years is the typical lifespan for a green roof, and is outlined in each graph. Conclusion/Summary 1)Initially, a green roof will incur greater costs than a traditional roof, as it is installed on top of an existing roof. Overtime, savings result from (a) stormwater retention, (b) heating costs due to insulation, and (c) extended life of roofing material beneath green roof. 2)The energy savings from a green roof should break even with the energy cost to produce the green roof during its lifetime. Furthermore, if energy costs increase over time, this breakeven point will occur sooner. 3)It is difficult to get clear data on the amount of nitrogen and phosphorus that are removed from stormwater runoff, but it does seem that green roofs do a better job of removing phosphorus from stormwater than nitrogen. 4)The larger the area of the green roof, the lower the cost per square meter. This is due to some of the flat costs associated with maintenance that do not increase as the size of the roof increases. At some point, the cost per square meter will decrease even more, as large roofing projects will get a discount on installation. More significant to the price per square meter is the amount of time the green roof lasts. Literature Cited Available upon request Acknowledgements This research was supported with funding from the National Science Foundation’s grant to NH EPSCoR (# ). Thanks to: Drs. Weiwei Mo and Stephen Hale for guidance on this project. Introduction/Background Green roofs are roofs that have vegetation installed on top of them. There are two types: extensive and intensive. Extensive roofs have shallower vegetation and are not meant to be walked on, while intensive roofs have larger plant growth and often have walking paths. I have chosen to focus on extensive green roofs, which are typically more cost effective than intensive, and compare costs and benefits associated with a green roof versus a regular roof. I used the green roof installation on James Hall as a model. There are many reported benefits to green roofs. A green roof can reduce stormwater runoff, insulate the building it is installed on, and increase the lifespan of the underlying roof. In addition to this, they are aesthetically pleasing, increase urban green spaces, and can even be used for food production. Methods Figure 5: Price per square meter per year Figure 3: Freshwater EutrophicationFigure 4: Marine Eutrophication Materials/Assemblies for 37 sq. m Green Roof Material SimaPro Entry Amount per tray Total amount Plastic Polyethylene, high density, granulate {RoW}| production | Alloc Def, U 29 kg2900 kg UV stabilizer Piperidine {GLO}| market for | Alloc Def, U kg14.5 kg Geotextile Polypropylene fibres (PP), crude oil based, production mix, at plant, PP granulate without additives EU-27 S kg3.78 kg Water Water, deionised, from tap water, at user {GLO}| market for | Alloc Def, U 9.46 kg946 kg Shale Expanded clay {GLO}| market for | Alloc Def, U 7.28 kg728 kg Loam: 40% Sand Sand {GLO}| market for | Alloc Def, U 8.74 kg874 kg Loam: 40% Silt Very fine milled silica sand d50 = 20 micrometer, production, at plant, median diameter of silica sand grains is 20 micrometers EU-27 S 8.74 kg874 kg Loam: 20% Clay Clay {GLO}| market for | Alloc Def, U 4.37 kg437 kg Zip ties Nylon 6-6 {GLO}| market for | Alloc Def, U 0.14 kg0.54 kg Pallet EUR-flat pallet {GLO}| market for | Alloc Def, U p Shrinkwrap Packaging film, low density polyethylene {GLO}| market for | Alloc Def, U 1.35 kg Box Truck Transport, single unit truck, diesel powered/US 2262 tmi Hoisting equip. Loader operation, large, NE-NC/RNA 1 day System Boundaries Life cycle assessment (LCA) is a method of quantifying and comparing the environmental impacts of various systems or processes used in our society. These “environmental impacts” come from the whole “life” of the system in question, including raw material acquisition, production, utilization, and disposal. The job of the person performing an LCA is to calculate the life cycle environmental impacts from the consumption of these resources at every phase in the life of the system. Life Cycle Inventory Information was obtained from the James Hall green roof system, information provided from the GreenGrid roofing company, as well as from a literature review. This information was used to estimate quantities of materials used in each tray on the James Hall roof. See table to right: Life Cycle Impacts SimaPro 8 was used to find the energy cost of construction of the green roof, nitrogen produced, and phosphorus produced. To calculate phosphorus and nitrogen produced in the construction of the green roof, I used ReCiPe Midpoint (H) V1.10 / Europe Recipe H in SimaPro 8. To calculate energy used for construction, I used Cumulative Energy Demand V1.08 in SimaPro 8. To calculate energy saved by a green roof, I used the literature for information. In a study with a green roof that is twice the size of James Hall had yearly savings of 967 kWh: To calculate the cost to produce the green roof, I used information gathered from the GreenGrid roofing company. For small roofs, they estimate $20 per square foot, or $215 per square meter. This would require about $800 for a green roof of this size. I ran the annual energy savings through SimaPro 8, again using Cumulative Energy Demand V1.08, to find the total yearly energy savings. Cost per kWh is the Eversource average for a commercial customer: To calculate the cost saved, I used information from the literature. An average regular roof would last 23 years and cost $81 per square meter. Thus, every 23 years, there would be a savings of $3000 since the underlying roof would not need replacement. To find the stormwater runoff savings, I used a study in the literature to estimate that 56% of the rainwater would be retained by the roof. The total annual rain based on Durham’s yearly average would be 43 cubic meters. The cost to treat stormwater in Durham, NH is $0.005 per gallon: Life Cycle Impacts (continued) To find the difference in maintenance cost for different areas of green roofs, I used the following formula: To determine the amount of nitrogen and phosphorus retained by the green roof, I first had to figure out how much rainwater the roof would get in a year: Using data from a study, I estimated that the eutrophication mitigated by the green roof was: For marine eutrophication: For freshwater eutrophication: