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SPUR Talk: Flowers and Butterflies on Market Street

4:03 PM PDT on November 1, 2022

A rendering of living roofs planned for Market Street. Image: Perkins Eastman Studio

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Imagine walking down a future Market Street that's quieter and greener, with western tiger swallowtail butterflies hovering above.

That may sound fanciful, but it's the goal of a living roofs project now underway for the tops of BART's new station canopies over the Market Street subway portals.  "New codes required that as they replace all the escalators that canopies are introduced to protect the escalators from the weather," explained Steve Line with Perkins Eastman Studio, during a panel discussion on the project this morning at SPUR. Safety regulations required that the canopies deter people from climbing on top of them during parades--but also be strong enough not to collapse if they do.

That also opened the opportunity, for a minimum of additional investment, to use the canopy as more than just a roof. "We wanted to create living roofs."

Note the utilities and access hatches on the roof. The green area will have to work around these.
Note the utilities and access hatches on the roof. The green area will have to work around these.
Note the utilities and access hatches on the roof. The green area will have to work around these.

Living roofs, with flowers and other greenery, make for prettier views for anyone looking down at Market Street from its many office towers. But it also means the city, with the right plants, can help freshen the air and attract birds and insects. "They will be elevated, habitat islands," explained Amber Hasselbring of Nature in the City and another of the panelists. "If we get all 23 of them built, the wildlife impact will be substantial. Imagine butterflies, birds, and other pollinators moving from habitat to habitat."

The Western Tiger Swallowtail. Wikimedia Commons.
The Western Tiger Swallowtail. Wikimedia Commons.
The Western Tiger Swallowtail. Wikimedia Commons.

Hasselbring explained that the concrete canyon of Market Street, to a butterfly, resembles a river basin or a natural canyon. The expectation is that if they plant the flowers the Swallowtails prefer, they will migrate to Market Street and travel from canopy to canopy looking for nectar.

"The fun part is the plants," said Kirstin Weeks with BioStudio LLC. "We’re looking at lots of beautiful flowering plants that flower in different seasons, plants that support the swallowtail."

The project had its origins in the necessity of removing some 50 of Market Street's trees to accommodate the new canopies. Advocates for Market Street demanded that some kind of greenery be put back in its place. "'BART you can’t remove all these trees without replacing them!' they said'” explained Hasselbring. "So the living roofs are part of that plan, along with tree replanting”

The canopies themselves cost about $2.2 million each. The greening of the roofs comes to about an additional $30 per square foot, added Weeks.

A reminder of why the roofs have to be strong in the first place
A reminder of why the new canopies have to be strong in the first place. Image: Perkins Eastman Studio
A reminder of why the roofs have to be strong in the first place

The panelists said the first couple of roof-greening projects should get done by the end of the year, with more to follow. The roof canopies will collect water for the plants during the rainy season, with built-in reservoirs to help get the native plants through the dry season. Ultimately, they should be more or less self-sufficient.

And sometime after that, "if all of this is successful, we’ll see butterflies on Market Street," said Weeks.

But still no protected bike lanes, unfortunately.

For more events like these, visit SPUR’s events page.

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