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September 2011 marks the three year anniversary of the opening of the new California Academy of Sciences museum. As the project landscape architect — led by John Loomis in our Sausalito office — we look back at the green roof design and its performance.

Living Roof Performance

Stormwater Capture

The 106,500 square foot green roof absorbs 3.5 million gallons of rainwater each year, reduces stormwater runoff by 93%.

Natural Building Ventilation

Cool air runs down the steep slopes of the hills on the roof, funnels it into the open-air plaza and vents warm air from the building through the skylights. Skylights are mounted with sensors that 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 and, thanks to the evapo-transporation of the retained moisture on the roof surface, animals and people benefit from its natural cooling effect.

Energy Production

The 60,000 photovoltaic cells that surround the living roof creeate shade for pedestrians below and generate approximately 213,000 kilowatt-hours of energy per year. This prevents the release of 405,000 pounds of greenhouse gas emission into the air.

Public Education

Its role in promoting public awareness of living roofs was part of the reason the project was awarded LEED Platinum certification. The museum expected to see 1.6 million visitors annually, but the actually visitor count has far exceeded those projections.

Native Habitat

The living roof is planted with nine native California plant species including Fragaria chiloensis, Prunella vulgaris, Armeria maritime, Sedum spathulitholium, Layia platyglossa, Lupinus bicolor, Eschscholzia californica, Plantago erecta, and Lasthenia californica. Each native plant attracts a variety of native insects, birds, moths, wasps, bees, and other bugs essential to the bay area ecosystem. We tested, with the help of our ecology consultant Rana Creek, a total of 25 native plant species on site for their resilience within the micro climate of the museums location. Read the California Academy’s living-roof habitat monitoring report.

Heat Island Mitigation

While evidence of heat island mitigation is anecdotal, The museum area is cooler than average surrounding area temperatures, but this could be largely attributed to its location within Golden Gate Park. The fact that the roof is irrigated to keep the plants looking good all year likely contributes to lower termperatures than if the plants were allowed to go dormant during the warmest months. The new building footprint is also 1.5 acres less than the original and these 1.5 acres were returned to the site as green space. On the flip side, arguments can be made that the building itself obstructs cool air movement from the ocean. There are currently no reports that confirm or deny these claims.

Cost Comparison

- The total project cost was $488 million.

- The final construction cost was $258 million.

- The cost of achieving LEED Platinum was 8 percent of the hard cost of the project.

- The cost of the green roof was $19 per square foot.

- The cost of the green roof construction was an additional $9-16 per square foot, yielding a total of $28 – $35 per square foot, approximately 3 to 4 times the cost of traditional roofs (including cool roofs qualifying for LEED solar reflectance credit), which cost approximately $6 to $10 per square foot.

Challenges

- The use of irrigation on the green roof over time is still subject to a debate. While the design intent is to remove irrigation systems and let the green roof run dry during the summer seasons (representative of a native California landscape) – the image of the green roof has become so iconic that the roof is still being maintained – and irrigated – today. The long-term vision is to remove the irrigation system.

- The roof can only be accessed through the elevator to the roof. Unfortunately, the maintenance crew has to use the same elevator – and there is no storage capability for supplies on the roof.

- It remains to be seen how the roof will last over time. Most buildings require long-term weathering and re-waterproofing. In 40- or 60-year’s time, what will be the procedure for updating and maintaining the roof and building, particularly one of innovative and unique construction?

- Deemed a “high maintenance superstar,” by writers such as Linda McIntyre (LAM), the roof is both celebrated and lamented for its high cost in time, money, and energy. While critics state that the cost is excessive and could have been used to implement a greater quantity of green roofs; McIntyre points out the difficulty of quantifying the success of a design that “captures the imaginations of millions of people,” that teaches and educates millions of people, communicating that design and sustainability matters and inspiring dozens of new green designs as a result.

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