Green roofs, also known as eco-roofs, living roofs, planted roofs or vegetated roofs, are quite literally roofs designed to support plant life. Over the past decade, an increasing number of leading architects, across Europe, America and Australia have been utilising this system to improve the performance of roofs and create environmentally sustainable buildings. On an overseas visit, midway through last year, AAA Volunteer, Vanessa Couzens, explored a building designed by Italian Architect, Renzo Piano. His building, the California Academy of Sciences in San Francisco's Golden Gate Park, uses a green roof to aid in the climate control of internal spaces. We thought this would be a great introduction to what can be achieved using green roofs.
A view across the California Academy of Sciences roof (Image by Vanessa Couzens)
In 2008 when San Francisco's California Academy of Sciences was rebuilt, Renzo Piano conceived of a domed roof covered by greenery. At the time this was quite a novel design for a vegetated roof and presented some real challenges in how to establish plants on the, quite steep in places, roof structure.
In keeping with the sustainable ethos, Piano was resistant to utilising plastic plant containers to hold plants in place. The consultant ecologist, Paul Kephart, resolved the problem of anchoring plants in position, utilising a biodegradable green roof module, made out of trays fabricated out of coconut fibre and held together with natural latex, that would naturally break down as plants developed root systems.
The California Academy of Sciences' roof is covered in California native species. The roof is used year round, for research and education. This meant that species selected needed to look good, virtually year round, to ensure that visitors remained engaged. Renzo Piano also wanted the roof to have a smooth, monolithic look, which meant that low ground hugging species were preferred. Over thirty species were tested, to establish the ideal plants for the harsh climate conditions and slopes on the roof.
Windows on the domes of the California Academy of Sciences (Image by Vanessa Couzens)
The Academy also wanted to create a habitat conducive to native insect life, particularly the endangered species of butterflies the Bay Checker-spot and the San Bruno Elfin. The comings and goings of flora and fauna are monitored closely by Academy staff and students from San Francisco State University. Monthly samples of insect life are taken along with the monitoring of plant species that show up on the roof without intervention.
Because of the very public nature of the roof space, it is constantly maintained and experience of seasonal variations in the ground covers has prompted the need to intervene, on occasion, by planting native flowering annuals that add interest and colour to meet visitor expectations.
Aside from the advantage of creating habitats for local flora and fauna, a green roof also offers great thermal advantages for the interiors of buildings. It slows the transfer of heat between exterior and interior, reducing and in some cases making obsolete, the need for air conditioning and heating.
In the Academy of Sciences substantial savings have been made in their use of electricity. Control of temperatures internally is further aided by the inclusion of computer operated porthole windows in the domes of the roof. These allow hot air to be released out to the exterior and also allow the building to be naturally ventilated.
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