On a recent trip to San Francisco I took the opportunity to visit a new rooftop urban park located on top of the Salesforce Transit Centre located in the central business district that incorporates a bus interchange and provision for a future high-speed rail station below.
Designed by PWP Landscape Architecture the 2.2 hectares rooftop park is about 440 m long and 50 m wide. Inclusion of the rooftop park was a key element in the winning architectural design by Pelli Clarke Pelli Architects (PCPA).
Drone view of rooftop park (Source - PWP web site)
A distinctive wavy perforated metal screen wrapped around the four level transit structure creates a strong visual contrast with surrounding buildings, particularly when seen from adjoining streets with the view framed by the walls of high rise buildings. The ground floor of the transit centre incorporates entrances, shops, ticketing and boarding platforms. The second floor includes retail space, a food hall, offices, ticket counter and waiting room. The third floor bus deck contains bus bays surrounding a central waiting area. The rooftop park forms the fourth level.
Multiple forms of access to the rooftop park include lifts, escalators, a free aerial tram from the street level and bridges connected to three adjacent high rise towers. Nevertheless I was very aware of the park being suspended in space, separated from the street level and visually more related to the surrounding high rise buildings than to the ground plane.
The rooftop park is a highly programmed space that provides activities that include an amphitheatre, restaurant, water features, play equipment and central plaza for use by transit passengers, office workers and local residents. Consequently it felt crowded as there is very limited opportunity to sit quietly away from the constant flow of visitors moving along the pathway that forms a loop around the park.
However, the pathway loop provides well orchestrated spatial experiences created by the combination of planting and structures with constantly changing views as you move along the curving alignment of the pathway.
Detailed planting adjoining the pathway presents a botanic garden character incorporating species that thrive in San Francisco's Mediterranean climate and the relatively protected rooftop environment surrounded by high rise buildings. The structure has been designed to support soil depths that allow the growth of large trees and shrubs. A notable aspect of the planting is the relatively high representation of Australian species. Perhaps this has resulted from the knowledge of Australian plant species gained by landscape architects in the PWP office through their involvement in the Barangaroo Headland in Sydney.
Storm-water runoff from the rooftop park, as well as grey water from the sinks in the terminal building, is collected and treated in a subsurface constructed wetland at the east end of the park. The water is then used in the restrooms throughout the terminal. Daylight is brought into the transit centre below via domed architectural skylights that are integrated into vegetated mounds in the rooftop park.
A feature of the Transit Centre is the inclusion of a public art program with five artists initially engaged and a budget of $4.75 million provided to fund the public artworks. The Bus Jet Fountain by environmental artist Ned Kahn expresses the movement of buses within the building on the level below though the activation of pop jets along the linear water feature. The apparently random timing of the pop jets provides obvious delight to children and engages most adults.
The discovery of cracks in a steel beam supporting the rooftop park in September 2018 provided a somewhat fortuitous opportunity from a landscape perspective as the rooftop park was closed until July 2019. As the landscape works had been completed before the closure, the planting had almost a year to become well established before the public again started to use the park.
