"The winning concept for the Basel Zoo Aquarium’s design competition is a restrained structure that plays with space and volume—and runs partially on solar power.
January 22, 2013—The design competition for the new aquarium structure at the city zoo in Basel, Switzerland, concluded last month; the winning design, “Seacliff,” is a partially buried, partially aboveground space that nestles into the urban environment without overpowering the neighborhood. The concept comprises a continuum of distinct spaces that enables visitors to walk through the exhibits sequentially and a restrained architectural style that does not compete with the sea life that will be on display—an important characteristic to the competition’s jury. Sustainability is another key component of the design; the aquarium will operate using solar and other renewable energy.
The winning concept was created by the architecture firm Boltshauser Architekten AG, located in Zurich, Switzerland, and was selected above a submission by the award-winning, London-based Zaha Hadid Architects, among others. Its long, narrow 1,150 m2 design will accommodate more than 20 exhibits focusing on the oceans of the world. It is designed primarily as a three-story underground structure, but part of this will be topped by a five-story aboveground volume. The underground portion extends not only beneath the five-story structure but also beneath a park that will be created between the main zoo building and the aquarium building itself. The curved five-story structure, which has a cantilevered entrance, will rise to a height of almost 25 m on the eastern side of the site, closest to the city.
The Basel Zoo is the oldest zoo in Switzerland and is among the leading zoos in Europe with approximately 1.7 million visitors annually, according to material included on the zoo’s website. Initially 55 teams applied for the competition, and 15 were selected to develop a full concept with the input of an aquarium specialist.
“The large area requirements for [the] aquarium’s program presented us with the great challenge to organize the building into a compact volume which would relate to the urban context,” said Roger Boltshauser, an architect and the owner of Boltshauser Architekten AG, who wrote in response to questions submitted by Civil Engineering online. “By burying a large part of the exhibition and technical spaces, we were able to keep the building volume reduced to a scale [that] directly responds to the surrounding urban context.”
The aboveground portion of the aquarium will connect to the local neighborhood and city with a public café and bar. A tank and habitat for sea otters will be located at the highest point of the building. Portions of the interior aquarium will be visible through openings created in the exterior façade, “intriguing and inviting passersby” to come and explore the aquarium, Boltshauser said.
The uppermost level of the underground space will house the technical equipment for the aquariums; assembling the equipment on one level keeps it from intruding on the standard visitor’s experience, and also provides an opportunity for special-interest groups to tour the inner workings of the aquarium, should they be interested in doing so, according to the architects.
The lower two underground levels will take visitors on a tour from the city of Basel to the sea, including tanks for plankton, jellyfish, schools of fish, a variety of crabs and snails, and a giant octopus. The spatial sequence of the exhibitions culminates in the largest aquarium space, the predatory fish tank, which will have stadium seating available for visitors.
The structural system for the aboveground portion of the building will be a double-skinned façade: the inner layer will be formed from load-bearing recycled concrete walls, while the outer, prefabricated wall will be made of rammed earth which has been created using trass (pozzolanic ash) as a binding agent, according to Alex Primas, a project manager for sustainability and energy concepts at Basler & Hofmann AG, the Swiss engineering firm that conducted the physics and sustainability planning for the project. Primas wrote in response to questions submitted by Civil Engineering online, adding that a layer of insulation will be sandwiched between the two skins. Clinker bricks—partially vitrified stones that are considerably heavier and stronger than regular bricks—will act as a brise-soleil at the windows to protect against direct sunlight in the summer and overheating of the spaces in daylight, according to the architects.
Concrete slabs—created from recycled concrete wherever possible—will be used inside the building as well, and nonloadbearing interior walls will be formed with rammed earth, using materials excavated on-site. Various other elements contributed to the sustainability of the project, according to Primas, including the compact building envelope and the durable, recyclable, and natural materials used in construction. The large building mass will handle loads efficiently and reduces peak demand on the heating and cooling systems, and primary energy consumption will be reduced by the integration of efficient energy systems, the reuse of waste heat as energy, and the use of heat pumps. Additionally, a large percentage of the energy used by the structure will come from renewable resources, minimizing CO2 emissions.
The building will be heated and cooled using a borehole heat exchanger and a rooftop photovoltaic system that will measure up to 600 m2 with an energy yield of up to 78,000 kWh annually, according to Primas. Finding a balance between the “high aesthetic and functional requirements of the building and the displays, and a low demand of primary energy for the building materials,” was one of the key energy challenges of the project, according to Primas. Another, and the most important for keeping the electricity demand low, was to limit the demand from the aquariums’ life-support systems. The former was accomplished with the materials selected for the building and the compactness of the design, while the latter was accomplished by making use of gravity to limit the electrical needs of the aquariums’ pumping systems, according to Primas.
Architectural details will add to visitors’ experiences, creating the sense that they are traveling a path through the earth as they move through the exhibit spaces, according to a written document provided by the architects that describes their competition entry. “The path [appears to be] a section cut through the earth, penetrating deep into the world of the sea creatures,” the statement says. “The interior rammed-earth walls are pressed with varied sedimentary layers, which represent the different compositions of the reef walls around the world.” On the topmost floors of the aboveground building, where the sea otter tank will be located, interior walls will represent the earth above water, according to the document.
During the next two years, designers will refine the winning concept and the zoo will seek permits for the project. Detailed planning will commence in 2015, according to the architects, and construction is anticipated to begin in 2017. Full completion of the project is currently planned for 2019.
The project is expected to cost 60 to 80 million francs (U.S.$65.8 to $87.7 million), according to Olivier Pagan, the director of the Basel Zoo, in a press release issued by the zoo announcing the competition winner.
In addition to the companies named above, additional work on the winning concept was conducted by Zurich-based Walt + Galmarini AG ETH/SIA (structural engineering); Maroochydore, Queensland, Australia-based Crossley Architects Pty. Ltd. (aquarium planning); Basel-based Waldhauser Haustechnik AG (mechanical engineering); Zurich-based Mueller Illien Landschaftsarchitekten GmbH (landscape architecture); Basel-based Gruner AG (fire protection); Mooloolaba, Queensland, Australia-based AAT Advanced Aquarium Technologies Ldt. (technical concept for life-support systems); and St. Gallen, Switzerland-based IBG Engineering (electrical and photovoltaic systems)."