Project Description
Location: Whipple Riverview Place, 25 Green Street, Ipswich, MA
Purpose:
- Demonstrate the effectiveness of vegetated or “green roofs,” in reducing rooftop runoff and nonpoint source pollution.
- Measure the storage of rainfall by the green roof.
- Measure 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.
Details: 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 with 3 to 4 inches of soil 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 section over the roof-access stairwell. The green roof is visible from the adjacent Ipswich Town Hall roof (accessible by permission only, during guided tours).
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
Site Photos and Planting List
Milestones
- Installation of green roof components completed, September 2006. Grand opening ceremony, June 2007.
- Runoff monitoring by USGS, June 2007 to October 2008
Costs
Engineering, installation, and the first two years of maintenance for the green roof:
- $100,000
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
- 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.
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 (amount of time without precipitation leading up to a storm) was found to be the main driver in how much rainfall was retained.
-
The effect on pollutant concentrations and loads varied and was generally not statistically significant. In fact, certain phosphorus compound loads appeared to increase from the green roof, possibly due to the organic matter in the soil or the fertilizer used to help the plants establish. (Fortunately, fertilizer application is expected to cease as the plants become fully established.) The results suggest that the water quality benefits of green roofs may lie more in the reduction in runoff volume than in the purifying effect of the runoff that does occur. The results also suggest that selecting appropriate roofing and soil materials and using fertilizers sparingly may further improve the quality of runoff from green roofs.
-
While not scientifically analyzed, the building managers observed lower energy bills than they had anticipated for a conventional roof, and credit the green roof with the savings.