Salesforce Transit Center Park

Challenge

• Create 5.4 acres of publicly accessible contiguous open space in a densely populated area that focuses on nature and living systems, allowing visitors to experience California native plants as well as plants from other parts of the world that are acclimated to the local climate.
• Design an ecological repository that provides wildlife habitat and attracts pollinators and migratory birds to the site.
• Design a fully accessible intensive green roof to detain and filter stormwater before it enters San Francisco’s combined sewer system.
• Encourage people at street level to use the rooftop park through design, programming, events, and activities.
• Reconnect urban residents and visitors with nature to improve their mental and physical health and promote well-being.
• Provide educational opportunities related to climate, horticulture, sustainable strategies, building technologies, geography, and environmental art through interpretive signage.

• The 5.4-acre green roof has soil depths that vary from 18 inches to 4.5 ft. This layered planting system is a structurally engineered component of the building that functions to balance seismic shifting, collect and filter stormwater, and irrigate the gardens. Geosynthetic fill was used to build up the rolling topography of the park while adding minimal weight to the structure.
• In order to create a topography that blurs the distinction between roof and ground, the park integrates mounded vegetated hills with domed architectural skylights that allow daylight into the terminal below.
• A constructed wetland at the east end of the park was designed to collect greywater from the restrooms within the transit center and to treat it for reuse in toilets and urinals in terminal restrooms.
• A curving concrete path leads visitors through a quarter-mile loop around the perimeter of the green roof, allowing for easy navigation.
• The park is easily accessible because of its location on top of a transit center and proximity to the bus depot and other transportation hubs including BART, Muni, Golden Gate Transit, and Amtrak. Bridges connect 3 adjacent towers directly to the park, allowing people in the tower offices above to descend directly into it.
• The rooftop supports 96,432 sf of pollinator and wildlife habitat encompassing 45% of its area. Much of this planting comprises California natives (11 California native tree species and 34 California herbaceous species) and includes plants such as island oak (Quercus tomentella), Calfornia lilacs (Ceanothus), sticky monkey-flower (Mimulus aurantiacus), and white sage (Salvia apiana). 600 individual trees and 16,000 plants are arranged in 13 different botanical feature areas including a wetland garden, an oak meadow, a redwood forest, and a desert garden. These gardens display the wide variety of plants that grow in California’s Mediterranean climate as well as the diversity of plants from the world’s 4 other Mediterranean climate zones. Because the plants are all adapted to a Mediterranean climate, they require significantly less irrigation than those in a typical park.
• Interpretive signage tells the story of the park. It teaches visitors about the climate, horticulture, sustainable design, building technologies, geography, and environmental art of the site.
• A public art installation called the “Bus Fountain” created by Bay Area artist Ned Kahn features 247 water geysers triggered by the movement of buses coming and going below. The 1,200-ft-long interactive fountain is one of the world’s longest water artworks.
• The grassy Amphitheater Lawn has room for more than 1,000 people to gather and watch performances on the Amphitheater Stage at the west end of the park.
• A bright yellow children’s play structure featuring a climbing rope frame and striped protective flooring is located between the Central Lawn and the Main Plaza, two of the site’s primary gathering areas.
• The walkable glass floor on the roof’s Main Plaza, the largest exterior glass floor of its kind in the United States, allows light to filter through to the building below. 
• The Salesforce Transit Center is a U.S. Federal Transit Administration “Buy America” project, meaning virtually every permanent piece, from the nuts and bolts in the structure to the drain mat and play equipment at the park, was manufactured in the United States.

• The idea of filtering greywater from the buildings adjacent to the park and using it to irrigate the rooftop park was originally proposed by the landscape architect within their initial design competition entry. At that time, however, the use of greywater for irrigation in commercial projects was not allowed per City of San Francisco code. The landscape architect was ultimately selected for the project, and, over the 8-year course of design, San Francisco plumbing codes were changed to allow greywater systems. This demonstrates that aspirational goals are worth putting forward within a design competition, and that risks can be rewarded.
• Early procurement and flexibility regarding plant species and sizes should be considered from the outset of a large-scale planting project. Because plant availability during the early design process (in 2008, before the recession) was demonstrably different from what was available when the documents were bid in 2015, substitutions had to be integrated into the planting plan while simultaneously maintaining the design goals of sustainability, botanical variety, and experiential character. Continued involvement by the landscape architect throughout the construction process coupled with a strong (but adaptable) planting design concept helped to accomplish these goals.
• The use of colloquial terms in contract documents can lead to misinterpretation and affect bid outcomes if such terms have different meanings from one discipline to another. “No-Mow” is a colloquial term for a kind of fescue that stays short without mowing. On this project a native fescue blend was specified for meadow areas that would not receive excessive foot traffic and would not require frequent mowing. Because the sod specified was called “No Mow” sod by the supplier, the contractor did not include periodic mowing in their maintenance contract. This became a problem when the fescue grew to be too tall and unkempt for the installation. Even this “No-Mow” sod required periodic mowing throughout the season due to the foot traffic that it received.

Drain Mat: Versicell
Foam: ACH Foam Technologies
Soils: Pleasanton Trucking
Stone: Coldspring Granite and Quarry SE
Metal Grating and Plant Rail: Olson Steel
Furniture: Blank and Cables, Bertoia
Play Equipment: Landscape Structures
Play Surface: Pebbleflex
Modular Trellis: Greenscreen
Building and Fire Life Safety Signage: WRNS
Interpretive Signage: Designed by PWP Landscape Architecture, built and installed by Architectural Design and Signage
Bus Fountain Glass and Grating: Progress Glass and Bilfinger Water Technologies

Project Team

Landscape Architect: PWP Landscape Architecture
Building Architect: Pelli Clarke Pelli Architects
Architect of Record: Adamson Associates Architects
Sustainability Consultant: Atelier Ten
Consulting MEP Engineer: BuroHappold
MEP Engineer: WSP
Environmental Graphics: WRNS
Cost Estimator: Davis Langdon / AECOM
Fountain Consultant: Fountain Source
Public Space Management: Biederman Redevelopment Ventures
Landscape Contractor: McGuire and Hester
Structural Engineer: Thorton Tomasetti
Environmental Planning Consultant: Rana Creek
Consulting Structural Engineer: Schlaich Bergermann and Partner
LEED Consultant: Integrated Environmental Solutions
Lighting: Auerbach Glasgow French
Irrigation: I.S.C Group

Role of the Landscape Architect

The landscape architect had a unique role in this project because it was located on-structure. Many architectural and engineering elements had to be coordinated with professionals from other disciplines like architects and engineers, including  the seismic joints, locations of elevators, and the balancing of the soil volumes and weights around the park for structural integrity. The landscape architect also undertook a great deal of coordination with the local city planning department and the public utilities commission around goals related to connections to buildings and the urban fabric at the ground level, as well as innovative sustainability and water  strategies for the roof. The landscape architect also completed a maintenance manual. The manual offers a design framework and aesthetic objectives for longer-term maintenance and management related to a landscape that is shaped and formed by plant material that grows and changes over time.