17 Trees Provide Shade and Stormwater Management in D.C. Capitol Hill Neighborhood

– A pedestrian-friendly, tree-lined, multiuse structure blocks away from the Capitol building in Washington, D.C., was completed in 2017.

– The 17 trees that surround 128 luxury residence buildings covering the entire block at 777 C Street St Pennsylvania Ave. SE help to achieve principles of new urbanism, support neighborhood activity, and well-being, and harvest site stormwater in the historically significant neighborhood.

– In addition to the positive changes the building development has made in the Capitol Hill community, the trees themselves have contributed many benefits to the climate and environment, growing exponentially in just four years. At the root of it all: Silva Cells.

The 2007 closing of Hine Junior High School presented a development opportunity rarely seen in the nation’s capital. After years of legal challenges from neighbors in the residential community anchored by Eastern Market, the district’s original farmers and art market, developers were able to proceed with a unique mixed-use, pedestrian-friendly space.

The development, designed by Esocoff & Associates + Weinstein Studio (now Gensler), and Oehme, van Sweden & Associates (OvS), aimed to meet LEED Gold and Silver certifications. Rising seven stories tall, the mixed-use space at 700 Pennsylvania Ave. SE sits across the street from the Eastern Market metro station with 17 trees surrounding its perimeter. OvS’ goal was for the street trees to develop a robust canopy, so naturally Silva Cells came into play.

The redevelopment site comprises a unique grouping of architecturally distinct buildings. The architectural context requires the site design and landscape to integrate seamlessly with the character of the surrounding neighborhood.

“We designed The Residences at Eastern Market to fit into the surrounding community by varying the façade types and paying homage to the Hill’s historic details,” —OvS

Although the design is rooted in the historical framework of Capitol Hill, OvS’ landscape includes many contemporary sustainable site elements, including systems of stormwater harvesting, urban forestry best practices, and green roofs. The urban forestry best practices included providing enough soil volume for the planned shade trees along the street.

The site is designed to incorporate the best principles of new urbanism and transit-oriented development. The new development enlivens the community, ensures a more pedestrian-friendly Pennsylvania Avenue and Seventh Street, and serves as a hub of neighborhood activity. With this high-density design construct, Silva Cells were the best way to provide for pedestrian-friendly shaded walks.

Wiles Mensch worked with OvS to create a SWM system that comprised multiple block faces. Given that OvS was installing Silva cells in an arboricultural application, it also made sense to use them for stormwater management, at minimal additional cost to that budget. Therefore, the design team had to deal with two district departments: Department of Energy & Environment (DOEE) and District Department of Transportation (DDOT).

DOEE requires that all the stormwater for a project within the district stays on-site, and DDOT has a soil volume standard of 1,500 ft3 of soil per large tree. This standard mandates the amount of soil volume per street tree, so real estate developer Eastbanc would not have been awarded its certificate of occupancy without providing that volume. In DDOT’s green infrastructure plan (page 178), a graphic explains the soil volume minimum policy.

Meeting the stormwater and soil regulations, given the design and project goals, was achievable only through the use of Silva Cells—especially given the pedestrian-friendly and high-density design for multiple programming types. There was little space or choice to keep the biorientation facilities as open swales. Particularly notable, Wiles Mensch got approval from DOEE for the bioretention equivalency with this design. (See Section drawing Silva Cell 1&2, above)

Ultimately, 378 3X Silva Cell Systems were used along the block of C Street SE, between Seventh and Eighth, for two large stormwater management (SWM) installations and three areas of tree soil volume application. There were a total of 12 trees in the SWM and an additional five for the street tree application. Each tree received 761 ft3 soil volume Wiles Mensch and OvS thus satisfied both regulatory agencies’ requirements with one product class and, more important, met the needs of Eastbanc with one budget item.

Installation Summary:
Number of Silva Cells: 378 3X
Amount of soil volume total: 12,950 ft3 (367 m3)
Soil volume per tree: 690 ft3
Number of trees and type: 17
Type of project: integrated trees, stormwater
Project designer: Oehme, van Sweden landscape architects
Project contractor:
Clark Construction
Installation date of Silva Cells: 2016
Project timeline: 2015–2017



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