The California Academy of Sciences stands as a leading scientific institution not only in terms of its research of the natural world, but also for implementing aspects those investigations into its architecture. Designed by Renzo Piano, it is remarkable because of its extensive network of sustainable systems. These include natural ventilation, radiant floor heating, heat recovery systems capturing and using heat produced by HVAC equipment, high performance glass, and reverse osmosis humidification systems. As a result of these intensive but discreet systems, the building was awarded the highest possible LEED rating, LEED Platinum, making it the largest such public building in the world.
But the most pronounced element that has shaped the image of the institution is its massive undulating green roof. There are over 2.5 acres of flora atop the building, the densest concentration of native wildflowers in San Francisco. It creates its own ecosystem by attracting native birds and insects. It enables natural light to penetrate 90% of the public spaces. It draws in cool air into the open piazza. Yet, how do these seemingly random elements work together in order to create a cohesive system? This assignment will focus on the green roof of the CAS and how its range of elements creates a dynamic system different from other similar roofs.
The roof of the CAS is both remarkable and unique because it is “living” in the sense that:
1. It creates an extension of the San Francisco ecosystem above and
2. Its gargantuan scale and shape create a dynamic climate system beneath.
Both above the roof and below it interact in order to create an exceptionally integrated system.
A view of the green roof.
What defines the topside of the academy’s roof and roots it specifically in this region is its incorporation of local flora. It establishes itself as a base for the development of a unique rooftop ecosystem that is not to be disturbed except for maintenance. Therefore, despite being artificially constructed, this green roof has the potential to give a glimpse of a diverse and abundant northern Californian ecosystem. The following methods that established this plant life are the reason for potential biodiversity.
There are two main types of green roofs, intensive and extensive. Intensive roofs are traditional roof gardens that are labor-intensive in terms of maintenance. Extensive roofs are more spread out in surface area, with shallower soil and substrate, requiring less maintenance and almost no irrigation, and appearing more functional rather than aesthetic compared to intensive roofs. The CAS has an extensive living roof. However, due to its undulating topography causing potential soil erosion, traditional means of simply overlaying the plant system on top was not possible. Each species of flora was therefore planted in a modular system of biodegradable trays made of coconut fibers harvested and assembled in the Philippines. There are about 50,000 of these 17” by 17” trays on the roof assembled on 2.5 acres in a puzzle-like fashion on six inches of soil. As the roots of the plants grow through the porous trays and interlock with one another and the layer of soil underneath, one large patchwork of vegetation is created.
The biodegradable coconut fiber trays.
In order to choose what species would both survive on the roof and be aesthetically pleasing all-year-round, 35 native plant species were grown in on mockups near the site with same microclimate. These were monitored for two years. Eventually, four perennials (seapink, beach strawberry, selfheal, and stonecrop) and five annuals (California poppy, tidytips, miniature lupin, goldfields, and California plantain) were selected. Each was chosen with the intent of attracting different kinds of wildlife. For instance, the stonecrop attracts threatened San Bruno elfin butterflies, tidy tips attract pirate bugs that feed on pest insects, and beach strawberries attract native birds. Thus the reason why the CAS’s roof is so remarkable is because it was intentionally designed to grow and become a part of the ecosystem of San Francisco. It takes a share in this system in one instance by preventing up to 3.6 million gallons of runoff from carrying pollutants into ecosystem (about 98% of all storm water). In other words, it makes the surrounding ecosystem of Golden Gate Park a little more resilient by adding to the amount of plants that can absorb runoff.
No one exactly knows how the roof will actually develop. This is significant because Piano wished to only establish a base for the system with just enough plants (1.7 million of them) and enough biodiversity to let it run on its own. The roof is meant to act as an ecological corridor that defines itself during its growth.
Looking from inside the central piazza.
The flows that occur on the underside of the roof are just as important as the ecosystem taking place on top of it. The sheer size and the undulating shape of the academy’s roof define the flow of air occurring inside in order to create a stable internal climate. As a result, a relationship is established on both sides of the CAS’s roof, setting it apart from many other green roofs as a multifaceted system.
Typically the purpose of a green roof is simply to act as a thermal barrier; however, Piano pushed the boundaries of the typology by making the roof “breathe.” It almost acts like a cell membrane by releasing and gathering energy for the interior. One of the major benefits of the CAS’s living roof is that it keeps the building’s interior an average of 10 degrees cooler than a standard roof due to thermal mass and natural ventilation. The mass of the roof includes layers of vegetation, anti-erosion fabric, soil, vegetation mats, water retention membrane, insulation, lightweight concrete, and an expanded metal sheet. Normal roofs would not include even half of these layers and would therefore lose more heat. The roof’s sloping geometry also creates a Venturi Effect by channeling in fresh air from windows and an open central piazza along two self-contained 90 ft. diameter spheres housing the planetarium and rainforest biome. The cycle of ventilation is completed by operable skylights above the spheres that release hot air. This system constantly cycles air throughout the building, improving air quality and comfort with reduced energy needs. As a result of the thermal mass of the structure, the geometry of roof, and the insulation it provides, natural ventilation becomes a viable climate-control strategy.A diagram illustrating how integral the undulating roof is in creating a stable, comfortable
Green roofs will have the greatest effect on energy consumption for buildings with relatively high roof-to-wall area ratios as is the case with the CAS. In fact, the building consumes 30-35% less energy than code in large part because of the sheer size of the living roof. Consequently, this among other effects illustrates just how potent Piano’s breathing green roof is. It is an efficient and clever system that serves multiple functions.
The California Academy of Sciences is a noteworthy building not simply because it has a green roof, but because it morphs that typology in order to create systems that shape each other both above the roof and below it. In other words, it pushes the green roof type by attempting to make it useful in multiple systems. The roof of the academy takes part in the ecosystem of San Francisco by transplanting native species on top of it and also uses that ecosystem to inform the movement of air within the structure. Both above and below the roof interact with one another, creating a rich network of sustainable systems.
Initial sketch by Renzo Piano.
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