Green Roofs at UMass Amherst

Brianna Lancaster- Animal Sci

Quinn Lonczak- ECO

John Yip- BCT

INTRODUCTION AND THESIS

If you have studied, lived, or worked at the University of Massachusetts Amherst, then chances are you have seen it. Running alongside Massachusetts Avenue, just south of the Intramural Athletic fields, it is now a normal presence. “It” is a grand stream of excess stormwater produced by the ever growing amount of impermeable surfaces on the campus. It is not formed naturally. It carries pesticides, contaminants, and other harmful substances directly into the Mill River and it can be abated. Increases in development of these impermeable surfaces prevent water from being absorbed into the ground as it naturally would. These surfaces force large quantities of water to flow and collect in smaller areas that are not necessarily designed to handle that quantity of water.

Stormwater can have many negative impacts on our campus. One major environmental impact is anything that enters a storm sewer system is discharged untreated into the water bodies we use for swimming, fishing, and potable water. Instead of entering the ground and being filtered naturally, stormwater runoff discharges directly into surface bodies of water. Stormwater runoff can also negatively impact the surfaces of our buildings and the environment in general. The common tactics to combat stormwater runoff are called Best Management Practices (BMP) (Environmental Protection Agency [EPA], 2009). One of the most effective BMP to combat stormwater runoff is green roofs. Green roofs have been scientifically proven to help reduce stormwater runoff (EPA, 2009). They also have many other benefits that would improve the quality of this campus. We strongly believe that the addition of green roofs on campus will greatly reduce the negative impacts of stormwater runoff. The UMass campus has already taken an initiative to install green roofs on most of its new construction. However, they have no plans of retrofitting the vast amounts of existing buildings with green roofs. We believe that the implementation of a green roof retrofit program will mitigate environmentally detrimental stormwater runoff on campus.

DEFINITION

Green roofs are termed low impact development (LID) by the Environmental Protection Agency (EPA). Urban and suburban development has led to large areas of impervious surfaces such as building roofs. Runoff from these areas is causing problems for many communities, including the University of Massachusetts. Greening of rooftops, by incorporating plants into the design of roofing systems, has been suggested as a method to reduce the impacts of stormwater runoff by reducing the impervious surface within a developed area (EPA, 2009). The benefits of green roofs for stormwater control include direct retention of a portion of the rainfall, and delaying and decreasing the peak rate of runoff from the site (EPA, 2009). This means that stormwater that would normally quickly drain off the roof and into a storm drain is either retained by the plants and substrates on the roof, or slowly infiltrated through the substrate and a later, a lesser amount, discharged into the storm drain.  Green roofs are classified into two categories, extensive and intensive, as described by the EPA. Intensive roofs are higher maintenance and more expensive than extensive roofs (EPA, 2009). They tend to be greater than or equal to 6-5 inches deep and can weigh 50 or more pounds per square foot. The vegetation can comprise of a huge variety of plants, including trees and shrubs. They are designed for gardening or social areas, such as rooftop garden areas in urban settings. They must be constructed on flat roofs and they usually require irrigation systems (EPA, 2009). Intensive green roofs would not be suitable for retrofitting buildings at UMass because of their costs and weight.

Extensive roofs require significantly lower maintenance as well and almost never require irrigation. They generally have a growth media with a depth of 2 to 6 inches and are usually around 13 to 50 pounds per square foot. Plants utilized in extensive roofs are not as varied as intensive roofs, including Alpine types (perennial grasses and sedges), succulents (cacti), herbs, traditional grasses, and mosses; all of which grow from 1 to 24 inches tall. This type of roof can be constructed on not only flat roofs but also on roofs with a slope of up to 30 degrees. They tend to be non-accessible as well as non-recreational (EPA, 2008).

Most extensive green roofs currently being installed in North America consist of four distinct layers: (1) an impermeable roof cover or roofing membrane; (2) a “drainage net”; (3) a lightweight growth media, which is about three inches thick; and (4) adapted vegetation such as hardy grasses (EPA, 2009). The drainage layer is an open, highly permeable material that quickly channels water off the roof. Growth media, in addition to providing a suitable rooting zone for vegetation, is typically a low-density aggregate with high-water holding capability which also provides good drainage (EPA, 2009). A lightweight media from 3 – 6 in. deep allows for retrofit installation on existing buildings, and reduces the need for extra structural support in new buildings (EPA, 2009). Media depth and porosity play an important role in stormwater retention and plant growth. Plants provide shade to the surface below them and intercept rainfall. Plant size and selection depend on the depth of the roof growing media and local climate, but in New England almost always consist of winter-hardy, drought tolerant perennial plants (EPA, 2009).

CAUSAL ANALYSIS

Why do we need green roofs? In 2012, over 60 inches of rain fell in Amherst (Massachusetts Department of Conservation and Recreation [DCR], 2014). Every drop of that rain that did not go naturally into the ground (grass, dirt, landscaped area), found its way into a storm drain of some kind. With over 11.5 million total square feet of building space, the University has a tremendous amount of roofing square footage which contributes hundreds of thousands of gallons of stormwater to the local waterways (UMass Amherst Campus Planning [UMass CP], 2013). Once drained off of the roof, the storm water is either carried via sewer directly into a surface body of water, or it runs along other impermeable surfaces such as sidewalks and roadways and into storm drains. While on that trip, the water can pick up excess pesticides, chemicals, or other hazardous substances; and deposit them into a waterway to ultimately will be used for swimming, fishing, or possibly even potable water (EPA, 2009). By mitigating the amount of water leaving a roofing surface, we could eliminate thousands of gallons of harmful stormwater from rivers and lakes in the area.

Some added benefits associated with green roofs are a reduction in heating and cooling costs, reduction in the heat island effect, buffering of the storm water pH, and providing an aesthetically pleasing area (EPA, 2009). pH buffering is significant in a place like New England, where our location downwind of the Ohio River Valley and its numerous power plants gives our rain an average pH of about 4.6, which is acidic (EPA, 2009). Clean rain is generally found to have a pH of about 5.6, and a neutral pH is 7 (EPA, 2009).  The EPA (2009) points out in an a study that “tests of the pH buffering capacity of the planting media suggest that the green roof media can buffer acid precipitation for approximately 10 years” (pg. 2-2), and with the simple addition of lime after that period, the material can buffer pH indefinitely (EPA, 2009).

There are few arguments that green roofs are ineffective. There have been hundreds of studies on the effects of green roofs and there is a general consensus that they are effective in combating stormwater runoff. For instance, Mentens, Raes, & Hermy (2005) argue in their article that “the use of extensive green roofs, even on only 10% of all roofs in a relatively green urbanized region, already reduces the annual runoff by 2.7%” (p. 223) as well as arguing that “the annual runoff reduction from single buildings is 54%” (p. 222). Also, in an article in the Journal of Hydrology, Hilten, Lawrence, & Tollner claim that storms with 0.75 inches of rainfall or less had a 100% retention rate when using a 4 inch deep green roof substrate (2008). The authors also claim that green roofs with a depth of 4 inches can provide water detention times of 12 hours for storms with rainfalls up to 3.91 inches (Hilten et al., 2008). This retention time creates lower peak flow, which is significant in reducing harmful erosion.

PROPOSAL

We propose retrofitting buildings eligible for such construction based on whether their roof structure is flat, the age of the building, and whether or not they are structurally sound enough to bear the load. Based on these factors, we believe a good starting point for this campus project is in the Southwest Residential area. Southwest contains 11 low-rise dormitories, each with about 18,000-20,000 square feet of total roof space. Completed during the 1960’s, the residential area houses 5,500 students, and is therefore very unlikely to be slated for demolition anytime in the near future (UMass CP, 2013). The buildings are constructed of stone and are structurally sufficient. Using ArcGIS software to delineate and calculate a suitable sized green roof, we surmise the average size the low-rise could fit is about 1,500 sq/feet of green space. Using cost numbers discussed later in this piece, we have calculated a cost for these specific buildings. At $19.00/sq. foot and adding in $1.25/sq. foot for the first two years, plus an additional 7.5% of the total cost for design, the retrofit could be completed for approximately $359,184. For that sum, the University would have created 16,500 sq./feet of new green space for storm water to infiltrate (EPA, 2009).

The implementation of green roofs can also become a research project for a coalition of majors and a mix of graduate students and undergraduates. Building and Construction Technology students and faculty could learn how to incorporate green roofs and other green concepts into projects and their future careers, and could even participate in the construction phase of the project. Civil and Environmental Engineering students and faculty could provide design planning support. Life Science majors could also benefit from this. For example, Microbiology students could use completed roof gardens to perform studies on microbial populations as well as develop sustainable cultures from the plants that are growing.  The Stockbridge School of Agriculture could also work with their students in finding species that can thrive and be self-sustaining in a green roof environment.

RESISTANT AUDIENCE

Many would be quick to point that the biggest obstacle to a project like this would be funding. Our rebuttal is two-fold: the cost of construction is not outrageous, and there are a multitude of grants to aid in the design and construction of green infrastructure. Retrofitting existing buildings with green roofs is not as costly as one might think. According to figures published by the EPA in 2009, an installation of an extensive green roof could cost $19.00/square foot, with a $1.25/sq. foot maintenance cost for the first two years only. Planning and design costs add on an additional 7.5% of the total. Using ArcGIS software to establish an average sized roof for buildings other than those in Southwest, we applied these numbers to calculate the costs for a retrofit of rather ambitious size: 3,500 sq. feet. The total cost, after the two year maintenance period, is $80,237.50. As additional suppliers and installers of green roof systems become available, costs are expected to decrease due to competition and increased availability. The EPA projected in 2009 that extensive green roof installation costs, which were ranging from $15-$20/sq. foot should drop to $8-$15/sq. foot as installations increased, and soil substrate and plants became more available (EPA, 2009). In contrast, a roof of the same dimensions would very conservatively cost about $6.00/sq. foot, or $21,000 to replace with traditional roofing (Coffelt & Hendrickson, 2010). This roofing of course provides zero mitigation of rainwater, no savings in heating and cooling, and would aid very minimally in eliminating the heat island effect.

Lack of funding is consistently cited as a barrier to the implementation of green roofs.  An advantage that green roof projects offer, however, is that they generate so many benefits that they can compete for a variety of diverse funding sources. Many federal and state grants exist to pay for the study, design, and construction of green roofs. The EPA Clean Water State Revolving Fund program has provided more than $4.5 billion annually in recent years to fund water quality protection projects for wastewater treatment, stormwater management, nonpoint source pollution control, and watershed management (EPA, 2014). Additionally, the U.S. EPA CARE Cooperative Agreement Request for Proposals grant system supports community-based partnerships to reduce pollution at the local level. Eligible applicants include universities, county and local governments, and non-profit organizations (EPA, 2014) Furthermore, the Department of Energy’s Weatherization and Intergovernmental Program provides grants, technical assistance, and information tools to states, local governments, community action agencies, and utilities. The program could be used to encourage green infrastructure, such as green roofs, as part of the weatherization process which is an added benefit of the green roof retrofit process (EPA, 2014).

Another argument against retrofitting green roofs onto existing buildings is that because of the constant stream of construction, most buildings will be torn down in the next couple of decades rendering the time and cost of installing the green roofs unnecessary. However we argue that the University would only build and install green roofs on eligible buildings that are not scheduled to be demolished in the next couple of decades, thus making them a somewhat permanent solution to the stormwater runoff problem. Buildings scheduled for roof replacement would be prime candidates.

On the flip side, there is an argument that some of these old buildings, even if they are not slated for demolition, may not be able to support the weight of a green roof system. There has been research into lighter, sturdier substrates that can be used for extensive green roof systems on buildings with a low load bearing capacity. In their article, “Quantitative Hydrological Performance of Extensive Green Roofs”, Wong and Jim (2014) studied the potential of a substance called rockwool in green roof systems. Rockwool is a highly porous synthetic mineral product that improves aeration and water-holding capacities (Wong & Jim, 2014). They explain that “[i]t is commonly installed between the drainage and substrate layers to improve retention capabilities and limit weight addition to the green roof system” (Wong & Jim, 2014, p. 367). They also researched the retention capabilities of rockwool. While their results did not specifically point to an immense increase in water retention, Wong and Jim (2014) believed that this was due to their research being conducted in the overly saturated, humid environment of Hong Kong. They propose further research into the capacities of rockwool in less humid environments.

CONCLUSION

We argue that retrofitting existing buildings with green roofs at UMass can be implemented for a reasonable cost by usage of state and federal green infrastructure grants, and also with the beneficial aid of several science and engineering programs already in place at the University. The University of Massachusetts has established itself as a pioneer in sustainability, and the implementation of green roofs will only boost the reputation of the school as an environmental innovator. If the school can help the environment, further educate its students in a sustainable field, and also further its standing as an environmental leader, then we believe this project is a win for students, faculty, and administrators.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

REFERENCES

Coffelt, D.P., & Hendrickson, C.T. (2010). Life-cycle costs of commercial roof systems. Journal of Architectural Engineering, 16 (1), 30. DOI: 10.1061/(ASCE)1076-0431(2010)16:1(29)

Environmental Protection Agency. (2008). Reducing urban heat islands: compendium of strategies. (EPA Publication No. 68/W-02-029). Washington, D.C.: U.S. Environmental Protection Agency.

Environmental Protection Agency. (2009). Green roofs for stormwater runoff control. (EPA Publication No. 600/R-09-026).  Cincinnati, OH: U.S. Environmental Protection Agency.

Environmental Protection Agency. (2014). Green infrastructure funding opportunities. Retrieved from http://water.epa.gov/infrastructure/greeninfrastructure/gi_funding.cfm

Hilten, R., Lawrence, T., & Tollner, E. (2008) Modeling stormwater runoff from green   roofs with HYDRUS-1D. Journal of Hydrology, 358(3-4), 288-293. DOI: 10.1016/j.jhydrol.2008.06.010

Massachusetts Department of Conservation and Recreation. (2014). Precipitation database [Data file]. Available from http://www.mass.gov/eea/agencies/dcr/water-res-protection/water-data-tracking/rainfall-program.html

Mentens, J., Raes, D., & Hermy, M. (2006). Green roofs as a tool for solving the rainwater runoff problem in the urbanized 21st century? Landscape and Urban Planning, 77(3), 217-226. doi:http://dx.doi.org/10.1016/j.landurbplan.2005.02.010

University of Massachusetts Amherst Campus Planning. (2013). A history of campus development. Retrieved from http://www.umass.edu/cp/cphistory.htm

Wong, G. K. L., & Jim, C. Y. (2014). Quantitative hydrological performance of extensive green roof under humid-tropical rainfall regime. Ecological Engineering, 70, 366-378. DOI:10.1016/j.ecoleng.2014.06.025

Evan

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