Turning a building typology on its heels can take a lot of conviction. Luckily, an unincorporated team of architecture students and recent graduates had no shortage of conviction when they entered an international competition to design a performance hall for a symphony orchestra, regional theater group, and opera in Kristiansand, Norway. As it turns out, the group’s idea to manifest the diverse program for the Kilden Performing Arts Center on the building façade was selected, leading to the foundation of ALA Architects in Helsinki.
Theaters often emphasize a “blank tower on the building that nobody will recognize,” says Samuli Woolston, a partner at ALA. “We wanted to bring out … the bellies of the actual shapes of the auditoriums, and how the seats rise and become visible on the surface.”
Designed in collaboration with local firm SMS Arkitekter, the 24,600-square-meter (265,000-square-feet) structure hosts a 1,200-seat concert hall, a 700-seat theater and opera hall, a 150-seat experimental theater hall, and a 235-seat multipurpose hall. The suite of spaces, which align in a row behind the lobby, is delineated by the undulating 3,500-square-meter (37,700-square-feet) wooden façade, which spans from the lobby floor to the 22-meter-tall cantilevered roof. The curves draw visitors into the performance halls, as if they were being “sucked into a cave,” Woolston says.
The dynamic surface is derived from two lines: the curved one that outlines the auditoriums at its base and the austere, 95-meter-long straight edge of the roof. Creating the double-curved form between the lines—with the curved line nearly twice the length of the straight one—tested the limits of modeling, fabrication, and construction.
The challenge fell to Zurich-based architectural and technology consultant Designtoproduction, which Norwegian timber contractor Trebyggeriet brought onboard, along with a Norwegian shipbuilder, Risør Trebåtbyggeri.
Steel framing, hung from the building’s concrete structure, supports the curved wood wall structurally. To create the furring system between the steel framing and the finished oak planks, Designtoproduction proposed using 10-meter-long glue-laminated spruce beams, which could be milled by CNC fabrication machines to within a 1/2-millimeter tolerance, says partner Fabian Scheurer.
Digitally fabricating the 1,803 glulam beams and 12,248 oak finished boards, which together comprise the wooden façade, required the consultants to model every aspect of the wall “down to the last screw hole,” Scheurer says. The team divided the furring system into 126 decklike elements, each comprising two straight header beams with nine to 13 curved beams in between. Seat cuts to align the oak planks were milled into the glulam beams, which average 120-millimeters-by-280-millimeters in section. Fabricated in Switzerland by timber consultant Blumer-Lehmann, the curved beams were transported to a shipyard in Norway, where they joined the Trebyggeriet-fabricated header beams and the Risør Trebåtbyggeri–fabricated oak planks.
The 21-millimeter-thick, 3-meter-long planks made from Norwegian oak—a reference to Kristiansand’s founding in the 17th century as a harbor to export wood to Europe for shipbuilding—were milled in sets of four on a five-axis CNC machine. To compensate for the differences in length between the wall’s defining curved and straight lines, the planks taper in width between 120 millimeters and 55 millimeters, but maintain the 10-millimeter gap between boards. “At some point, the boards would become too small,” Scheurer says. Once the planks taper to 55 millimeters, a new 120-millimeter board picks up where two planks left off.
The long edges of the oak planks were also angled to accommodate the surface’s inward and outward curves. As many as 180 planks fit on each furring element. Each plank was slightly bleached and then re-dyed to help preserve its rich, uniform color from fading due to exposure to the sun and Norwegian winters, Woolston says.
Risør Trebåtbyggeri then preassembled the elements in its shipyard, where the prefabricated assemblies could be easily transported on barges to Kilden’s waterfront site 100 kilometers away. If all went as planned, the assemblies would “snap into place, just like an Ikea building kit for 126 façade elements,” Scheurer says.
To mitigate the difference between the 15-millimeter tolerance in the steel-frame construction and the 2-millimeter tolerance allowed in the finished ceiling gaps, Designtoproduction fabricated each furring element with eight connection points that allowed for some play during the wall installation. “Unfortunately, the human eye is pretty good at seeing non-straight lines,” Scheurer says. In the end, the team’s meticulous planning and assembly paid off: Only one of the 126 elements required a slight modification.
While the wooden façade appears to run continuously from the building interior to exterior, the glass curtainwall actually truncates the oak planks, creating a clean break between inside and outside members. The curtainwall stops shortly once it disappears above the finished wood surface to avoid interfering with the steel framing. The curtainwall is supported on grade, allowing the wooden façade to move freely, not only to accommodate thermal loads but also loads from “heavy winds blowing down from the fjord,” Woolston says.
The intersection of the glazed and wooden façades at the outside corners of the building also proved to be one of the design’s greatest fabrication challenges. The return of the curtainwall into the cantilevered wooden façade creates a diagonal intersection that runs the height of the glazing. “In those corners, you have double-curved elements” where the furring elements are no longer planar curves, but spatial curves that bend in two directions, Scheurer says.
The graceful movement and materiality of the wave wall, which took about 18 months to complete, belies its complexity. Downplaying the wall as a “huge eaves structure,” Woolston says that “the most interesting part was the collaboration with Designtoproduction and the way of using two very simple lines to create a big surface.”