A Park in the Sky | Inside the Minds of the Landscape Architects Behind the Salesforce Transit Center Park

In this article, discover the design considerations behind the Salesforce Transit Center rooftop oasis and how PWP Landscape Architecture was able to produce one of the world’s standout rooftop ecosystems.

The New York City High Line is considered to have popularized the concept of greenspaces above ground level. The High Line has a long history that includes being used as a railway until it was mostly abandoned in the 1980s. Thanks to the advocacy and planning of some forward-thinking individuals, the High Line was reimagined into a public open green space which opened in phases in 2009, 2011, and 2014.

Lost in the conversation, though, is San Francisco’s Salesforce Transit Center rooftop greenway, the conception of which dates back to a design competition in 2007. Each has merit to be considered the exemplars of above-ground greenspace, alongside the Promenade Plantée in Paris.

This article will explore how this project came to be, with insight from the project’s landscape architects of PWP Landscape Architecture.

PWP Landscape Architecture has been a leader in the field of landscape architecture for decades. Established in 1983, this world-renowned firm has a pedigree that includes dozens of iconic projects from around the globe ranging from urban parks to corporate landscapes and ecological restorations. Their portfolio is truly impressive, having won countless awards and accolades along the way. Notably, they’re credited with the design of the National September 11 Memorial in New York City, which stands as a powerful symbol of remembrance and healing. Whether it is restoring an old garden or creating something entirely new, PWP has time and time again demonstrated the ability to bring beauty to a space and craft unforgettable spaces for people to enjoy.

“Creating places and landscapes that better the world is a goal that we have,” said Adam Greenspan, FASLA, design partner at PWP.

There are apparent limitations to designing a lush greenspace above ground level. It requires excellent collaboration with engineers, ecologists, and architects not only to provide plantings and wildlife with the resources they need to thrive in perpetuity, but also to ensure that the project has structural integrity.

Vectorworks Landmark allowed PWP to accurately account for the work of these consultants, ensuring their essential knowledge informed the landscape architecture process.

“Vectorworks is like a language,” said Cornelia Roppel, a lead designer on the Salesforce project. “It can show and demonstrate what you want the end result to be.”

Roppel explained that methodology at the beginning of PWP’s projects can vary, whether they start from drawing with pencil and paper or by examining the site in Google Maps or via a site survey. Whichever method they take, each results in importing files to Vectorworks Landmark.

“The advantage to the software is that you’re able to create good graphics instantly and at scale,” Roppel said. “As we draft these things, we know the sizes of steps, we know the sizes of walkways, we know the sizes of trees and shrubs. Sometimes we end up with eight to ten different design options in one file, which we study and narrow down to two or three. Studying these options graphically and discussing design opportunities is what we do using the flexibility of Vectorworks.”

Located in downtown San Francisco, the site for the Transit Center project used to lurk in the shadows of the skyscrapers surrounding it. It blended in; unquestionably, downtown San Francisco was exactly what you’d expect when you consider dense urban areas — a sea of high-rises and near-maximum efficient use of available space.

“This four-and-a-half-acre rooftop was something we thought could be a great amenity for the neighborhood. It would sequester carbon and simultaneously create a better environment for the people that were going to be living there and visiting,” said Greenspan.

The Transit Center rooftop paves the way for an interrogation of urban identity by its very presence. Are buildings more important than nature? Who’s to say we have to choose?

Signage along the rooftop, which provides information about plantings and wildlife throughout the semi-isolated ecosystem, encourages visitors to consider these questions as well. Ultimately, the project invites a stepping away from normalcy of urban life to consider nature’s essential role.

The Transit Center brings practical sustainable solutions to downtown San Francisco in several forms.

Stormwater and water from terminal sinks are collected and treated in a subsurface wetland at the park’s east end. This water is then used for restrooms throughout the terminal building.

Before this project, San Francisco code disallowed the use of greywater in commercial applications. It was only permitted for reuse in residential situations. PWP worked with San Francisco City Planning to demonstrate the benefits of greywater reuse in all areas of city planning — ultimately the code was changed, and much of the switch can be attributed to the efforts of PWP.

The Transit Center also improves the environment by absorbing bus exhaust from the terminal below it.

The micro-ecosystem has become home for birds, butterflies, and pollinators, increasing biodiversity and longevity of the rooftop park. Greenspan explained the conception of this biodiverse ecosystem:

• “We took the history, heritage, and ecology of San Francisco and the Bay Area very seriously on the development of this project. We wanted to create a park with special gardens that appeal to both people and animals.
• Native California species are very important to that end, but so are non-native species. The non-native plants we included have all evolved to live in very similar climates to the Bay Area, whether they’re from Mediterranean climates, dry summer and desert-like climates, or high-elevation forests. None of the species used are invasive; they’ll all remain contained to the rooftop.
• Many of the plants, even the non-native ones, are used as resources for native animals. We did a tour with a biodiversity specialist who pointed out that a bird species native to San Francisco eats plants from Australia to get them through various periods. They come to the rooftop because there are so many plants and trees flowering, including the native-to-Australia ones they’re looking for.”

There are over 50 species of trees and over 230 species of understory plants. Here you can find a complete PDF of all the plantings present in the rooftop garden, divided by area.

It’s clear that the Salesforce park is eye-catching — years of forethought and planning went into the creation of this marvelous ecosystem.

Since the rooftop spans around four city blocks and 5.4 acres, it contains several distinct sections that ease into each other.

“The outer edge of the park is surrounded in a series of gardens, and those gardens are feature gardens that focus on plant communities and plant types that are specifically suited to San Francisco's climate that also are available as habitats for flying members of San Francisco,” Greenspan said.

Another captivating feature of the rooftop is the system of water jets that shoot upwards whenever a bus passes underneath. As a bus drives through the bus deck level, it triggers sensors in the ceiling that then shoot water on the roof. You can actually follow the speed of the passing bus by watching the line of jets shoot water upwards.

“We were really focused on creating something that wouldn’t bring down the neighborhood but would help uplift it,” said Greenspan.

Learn more about PWP Landscape Architecture.

Learn more about Vectorworks Landmark.