by Leah Fessenden, Use Your Roof Intern

The rainfall on a recent winter day lent an additional element of awe to the living roof system on top of the California Academy of Sciences. Its presence allowed a glimpse of the complete benefits the green roof provides- native habitat space, energy efficiency, and stormwater treatment were all on view. Bay Localize colleagues took it in on a tour of the perimeter, and gleaned inspiring tidbits from the roof's caretaker, CAS employee Kendra Hauser.

We geeked out just the tiniest bit, and this magnificent green roof is veritable cause for stampedes: at just over a year old, the museum’s rooftop has provided millions of visitors with information on the habitat and multiple benefits of that the living roofs can offer. And it goes further. San Francisco public policy makers are beginning to realize the numerous payoffs afforded by these systems, which have already been pioneered by cities across the country, and are penciling green roofs into long-term strategies. The newly drafted Stormwater Management Ordinance and Stormwater Design Guidlines, currently working their way to the Board of Supervisors, bode well for new green roofs filling in the patchwork of rooftops across the city.

The roof at the California Academy of Sciences certainly sets a stunning example to follow. The design was a collaboration between architect Renzo Piano and the ecological design firm Rana Creek. The result is a living roof of 2.5 acres, sited complete with rooftop hills with slopes of up to 60 degrees, several microclimates, 1.7 million plants comprised of 80 different native species and four productive beehives.

It is its role as an evolving native habitat that makes the roof an asset to the local ecology. Since installation in 2008, the living roof boasted a higher concentration of native insects than are present in the adjacent park at ground level. As it matures, different plants may predominate in different sections than in these first few seasons, and correlating cycles of insect and bird species will provide rich material for viewers and scientists to reconnect with a native habitat.

The plants, insects and native ecosystems are not the only ones benefiting from the presence of the living roof. The six inches of soil reduce the energy needs of the 400,000 square foot building by approximately ten percent through decreased demands of the cooling and heating systems. Over the course of its first year, the roof retained 98% of its rainfall, preventing 3.6 million gallons of water from entering the stormwater system. Especially during the El Nino season, this onsite stormwater retention reduces stress on our watershed and lowers costs for municipal wastewater treatment. And San Francisco is planning for wider implementation of green roofs to see those benefits city wide. Under the proposed Stormwater Management Ordinance, new and redevelopment projects above a threshold of 5,000 sq ft of ground surface disturbance will soon be required to meet onsite stormwater treatment goals which includes green roofs as a strategy.

The benefits have been proven and accepted; the popularity of green roofs beyond the California Academy of Sciences is apparent. Bay Localize and our allies at the newly-formed Green Roofs Alliance spoke before the SFPUC, which unanimously voted in favor of our proposed amendment to further promote green roofs as a stormwater solution. It is clear that there will be a greener skyline in San Francisco’s future, an important stepping stone for the rest of the Bay Area to follow suit. Even more exciting, SFPUC staff have expressed a desire to work with advocates to include green roofs more prominently in city ordinances, property-based financing programs, and other policies in the months and years ahead.

Still, infrastructure like green roofs often have high installation costs, so the role of first wave demonstrations sites like the rooftop at California Academy of Sciences are important to increase the public’s awareness of the possibilities that exist and inform them of the benefits. But without strong leadership from other regional municipal governments, these projects are out of reach for most Bay Area residents. Cities across the country, from Portland to Philadelphia, are encouraging green roofs by using incentives, rebates, building code and stormwater ordinances. San Francisco is the first major Bay Area city to develop a guideline that sets requirements and encourages green roofs. Other governments should consider leveraging green building codes that promote green roofs as a multi-prong strategy; energy efficiency incentives; expedited permitting or Floor Area Ratio bonuses to developers including green roofs into their projects; or for cities that already have a stormwater fee, develop discounts and incentives for properties that incorporate onsite stormwater treatment.

Our recent visit to the Academy of Sciences planted in my mind how definitively green roofs are ready to materialize in a big way in the Bay Area. Bay Localize will continue to advocate for green roofs as sensible infrastructure ready to take root in our communities, for the holistic health of our urban habitats.