By Steven Peck
with Damon van der Linde
As the Net Zero Energy building concept has gained some popularity over the years, I would now like to call attention to the equally important, up-and-coming idea of Net Zero Water design. The concept implies achieving water independence and mitigating stormwater run-off, which puts green roofs in the position of being one of the most powerful tools to accomplish this, especially on a large scale. Net Zero Water is one of the more difficult factors of the International Living Building Challenge and has been stated as a target for the City of Seattle Department of Planning, which isn’t surprising considering the negative effects of improperly mitigated stormwater.
Studies have shown that a traditional roof’s run-off contains high concentrations of pollutants from rainwater, roofing materials, and atmospheric deposition. By delaying, capturing and temporarily storing stormwater, green roofs can reduce run-off volumes and meet regulatory requirements. The plants and growing media used in green roofs help decontaminate run-off, loading fewer pollutants into the municipal stormwater system. By increasing stormwater retention, green roofs can also reduce the need to expand or rebuild related infrastructure.
Many older cities have combined sanitary and storm sewers, whose treatment capacities are often overwhelmed by heavy precipitation. By reducing run-off, green roofs can limit the occurrence of combined sewer overflow (CSO) events, and thereby diminish the quantity of untreated wastewater entering fresh water bodies. By reducing peak flows during storm events, green roofs can also help to reduce the incidence of flooding. Green roofs save money by increasing stormwater retention and decrease the need to expand or rebuild related infrastructure.
Due to the reduced quantity of stormwater run-off, smaller roof drains may be possible on a green roof. A study in the Washington D.C. area showed that a three-inch-deep extensive green roof retained between 65 and 85 percent of stormwater run-off compared to a conventional roof. The amount of stormwater retained depends on factors such as depth and composition of growing media, type and coverage of plants, and type of drainage system. The excess stormwater can then be collected on the roof or in cisterns below and later used to irrigate the vegetated areas, reducing the use of potable water for this purpose.
Increasingly, jurisdictions such as Philadelphia and Minneapolis have begun to implement Storm Water Utility Fee charges, which help raise capital for improved stormwater management and provide financial incentives for building owners to reduce run-off. The fees assessed to each property owner are typically based on the impervious surface area of the property. For commercial and industrial buildings, the large amount of impervious surfaces often results in larger new stormwater fees, which can be a significant cost over a 20- to 40-year period. Stormwater fees can provide a monetary incentive for the use of best management practices.
Integrated Water Management Seminar for Buildings and Sites
Green Roofs for Healthy Cities has developed the Integrated Water Management Seminar for Buildings and Sites, with the American Society of Irrigation Consultants (ASIC), to leverage additional government and public awareness by providing technical and economic information on the design and performance of a fully integrated site and building water management system based on the “Net Zero Water” concept.
This course is lead by Jeffrey L. Bruce, FASLA, GRP, President of Jeffrey L. Bruce & Company and Lynda Whiteman of Hunter Industries. While there are numerous regulatory challenges, this approach promises to significantly reduce the consumption of potable water in buildings, reduce discharge to municipal waste water systems, and save on municipal energy by reducing the amount of potable water treated at municipal facilities. The seminar provides information on how to develop and efficiently manage limited water resources in order to deliver truly sustainable living systems to the urban environment.
The Integrated Water Management Seminar for Buildings and Sites will be delivered at the 8th Annual CitiesAlive Green Roof and Wall Conference in Vancouver BC on December 1, 2010. The course is currently undergoing peer review and will eventually be available at the Green Roofs for Healthy Cities’ Web site as one of many educational seminars and courses on the Living Architecture Academy, our online educational facility.
The Integrated Water Management Seminar for Buildings and Sites can be used as continuing education credits for the Green Roof Professional (GRP) accreditation designation. The GRP program is a unique learning opportunity for landscaping and irrigation practitioners to further their involvement in green roof design and maintenance, securing a vital role in the sustainable construction industry. Launched in 2009, the GRP accreditation is supported by four professional development courses offered in different locations throughout North America. The importance of integrated water management with the goal of Net Zero Water will only increase in the near future and design and installation professionals will be needed to respond to this demand.
Steven W. Peck, GRP, HASLA, is founder and president of Green Roofs for Healthy Cities. The association has more than 5,000 members and has completed several initiatives designed to generate a market for widespread green roof infrastructure implementation.
Damon van der Linde is a communications and research coordinator for Green Roofs for Healthy Cities.
For more information, visit www.greenroofs.org