Location: Whipple Riverview Place, 25 Green Street, Ipswich, MA
- Demonstrate the effectiveness of vegetated or “green roofs,” in reducing rooftop runoff and nonpoint source pollution.
- Quantify the storage of rainfall by the green roof.
- Quantify pollutant removal associated with the green roof.
- Reduce nonpoint source pollution to the Ipswich River, immediately adjacent to the property.
- Improve energy efficiency of the building (not quantified for the purposes of this project)
Description: The green roof demonstration site, Whipple Riverview Place, is a former school building, which was redeveloped as affordable housing for seniors, by the North Shore Housing Trust (now Harborlight Community Partners). The green roof was installed as an example of an “extensive” (as opposed to “intensive”) system, with 3 to 4 inches of soil medium and 10 varieties of low-growing, drought-tolerant plantings, including 8 varieties of sedum, accented by chive (Allium schoenoprasum) and fame flower (Talinum calicynum), which provide height, color, and texture. Underlying the plantings are a waterproof membrane, drainage mat, filter fabric, and soil medium. The green roof covers the entire rooftop, approximately 3,000 square feet, including a steeply-pitched stairwell headhouse. The green roof is visible from the adjacent Ipswich Town Hall roof (accessible by permission only, during guided tours).
Data Collection and Analysis: The U.S. Geological Survey (USGS) collected runoff samples from the green roof to assess both the quantity and quality of runoff. Water quality samples were analyzed for a range of parameters, including conductivity, pH, nitrogen, phosphorus, metals, and total petroleum hydrocarbons. The data from the green roof were compared to data from the conventional roof at Ipswich Town Hall to assess the effectiveness of the green roof in reducing rooftop runoff and removing pollutants.
Green Roof Planting List: Almost 6,000 plugs representing ten plant species and cultivars were initially planted in September 2006:
Quantities are listed in parentheses:
- Allium schoenoprasum (630)
- Sedum album (700)
- S. floriferum ‘Weinenstaphaner Gold’ (630)
- S. hybridum ‘Immergrunchen’ (630)
- S. kamtschaticum (630)
- S. middendorffianum diffusum (630)
- S. rupestre ‘Angelina’ (630)
- S. spurium ‘Summer Glory’ (350)
- S. spurium ‘John Creech’ (560)
- Talinum calycinum (560)
- Installation of green roof components completed, September 2006. Grand opening ceremony, June 2007.
- Runoff monitoring equipment installed by USGS at both the green roof and conventional roof, November 2006.
- Runoff monitoring by USGS, June 2007 to October 2008
- Number of rainfall events sampled for water quality: 10
- Maintenance of green roof plantings performed, summers of 2007, 2008, and 2009
Engineering, installation, and the first two years of maintenance for the green roof: $100,000.
Key Results and Conclusions:
- The green roof delayed runoff and captured anywhere from 20% to 100% of rainfall (including 100% of a 2-inch storm!)
- The green roof retained more than 50% of the volume of most storms.
- Almost 100% of the rain falling on the traditional roof ran off quickly.
- Antecedent dry conditions were found to be the main driver in how much rainfall was retained.
- The effect on pollutant concentrations and loads varied and results were largely not statistically significant. Certain phosphorus compound loads, however, did appear to increase, possibly as a result of organic matter in the soil or the fertilizer applied to help the plants establish. Fertilizer application is expected to cease as the plants become fully established.
- A sampling bias toward storms with a higher percentage of runoff limited the ability to characterize the impact of the green roof on annual loads.
- The building managers have observed lower energy bills than they would anticipate with a conventional roof, and credit the green roof with the savings.
Publications and Materials:
- USGS Scientific Investigation Report 2010-5007
- USGS circular
- Ipswich River Targeted Watershed Grant Fact Sheet: Green Roof Case Study
- Interpretive Sign
Developer: North Shore Housing Trust, Newburyport, MA (subsequently merged with Harborlight Community Partners, Beverly, MA)
Designers: K.J. Savoie Architecture, Ipswich, MA
Construction: Magco, Inc., Jessup, MD
In-kind cooperation: Town of Ipswich
Monitoring and Analysis: U.S. Geological Survey
Maintenance: Apex Green Roofs, Somerville, MA