Three years ago the California Academy of Sciences museum re-opened in San Francisco. The original projections of annual visitors were for 1.6 million, a head count that has been far exceeded in the past three years. Some of the building’s popularity is undoubtedly due to its iconic 2.5 acre-“living roof”, celebrated in the early reviews for its innovative energy saving properties. The roof was, however, criticized for the high price tag it came with, and the unknown cost of its future maintenance. The technology used in this design is a part of the museum’s educational curriculum and it’s been the model for other green roofs since its completion. If green roofs are going to be a viable part of the infrastructure systems of our cities in the future, we need to openly evaluate what is working and what isn’t.
The California Academy roof contains enough solar panels to prevent the release of 405,000 pounds of greenhouse gases per year. The large glass canopy that surrounds the living roof contains 60,000 photovoltaic cells. The arrangement of the panels on the canopy shades pedestrians below and generates some 213,000 kilowatt-hours of energy per year.
In addition to energy savings, the roof helps cool the interiors beneath it. Those eye-catching mounts send cool air down into the open-air plaza while warm air from inside the building vents through the skylights. Sensors in the skylights gauge the interior temperatures and automatically open at a given threshold. The roof keeps the interior temperature an average of 10 degrees cooler than a standard roof would.
The 106,500 square foot green roof absorbs 3.5 million gallons of rainwater each year, a stormwater runoff reduction of 93%.
But does it mitigate the urban “heat island,” as green roof proponents promise? While studies show that expansive use of green roofs in a city can help cool air, this particular roof is in the middle of Golden Gate Park and not in an urban area where green roofs offer the most potential for heat island mitigation. Anecdotally, the fact that this living roof is irrigated year-round does contribute to lowering temperatures, both inside and around the building. And since the new building’s footprint is 1.5 acres less than the original building was, the acres returned to the site as green space help cool the area.
Even with all the advantages of the living roof, there are a few controversial items related to the project that are still subject to debate. While year-round watering contributes to cooling the building and its surroundings, the original intent was less resource intensive. Significant effort and testing went into creating a native California landscape on the roof, using plants that are indigenous to the area and that would survive its particular micro-climate. The design proposed that the plants would go dormant during the warmest months. But as long as the allure of the green roof is in its “greenness” it will be difficult to pull the plug on irrigation and the Academy misses the opportunity to educate the public that the green roof’s native plants have a dormant season.
Something for the Academy to consider: integrate semi-native, adaptive species that are evergreen and / or flower during the time when the native grasses go dormant. It goes against the “all native” approach, but perhaps this is true aesthetic of sustainability.
Also under debate is how the roof will hold up over time. Most buildings require periodic weathering and re-waterproofing. And since this is such an innovative project, it’s hard to predict the procedures that will be needed in 40 or 60 years to update and maintain the roof and building itself.
Dubbed a “high maintenance superstar” by Landscape Architecture Magazine, the living roof at the Academy of Sciences cost almost twice as much as a traditional green roof does. Typically, such roofs cost $15 – $20 per square foot versus the $28 – $35 per square foot for this living roof. With the unknown maintenance and upkeep costs in the future, the roof could continue to be expensive.
My suspicion is that much of the Academy’s green roof maintenance budget is spent pulling weeds and replacing plants. Perhaps the Academy could structure a funding program aligned with local universities (e.g. the funding grants come through the universities) offering students a chance to learn about green roof technology via a set of stewardship initiatives that could, among many things, include pulling invasive plants. This approach could free the Academy of out-of-pocket expenses and further its commitment to education.
Even with these drawbacks, the roof effectively teaches millions of people, communicating that design and sustainability matter. Its form and construction have inspired dozens of new green designs. These positive outcomes cannot be quantified by the price per square foot method. After all, the roof’s role in promoting public awareness of living roofs was part of the reason the California Academy of Sciences project was awarded LEED Platinum certification.
Gerdo Aquino, ASLA, is president of SWA, an adjunct associate professor of the Master of Landscape Architecture program at the University of Southern California and the co-author of Landscape Infrastructure (Birkhauser 2011). John Loomis, ASLA, SWA’s Sausalito office, was the landscape architect for the new California Academy of Sciences building.
Image credits: ASLA 2009 Professional General Design Honor Award. California Academy of Sciences. SWA Group / Tom Fox