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Underground Gym Creates Courtyard ‘Hill’

The Gammel Hellerup Gymnasium's curved wooden hilltop roof, comes complete with seating and gather space for students
A new 1,100 m2 concrete gymnasium at the Gammel Hellerup Gymnasium, a high school in the suburbs north of Copenhagen, has been embedded 5 m into the ground so that its curved timber roof can be used as a wooden ‘hilltop,’ complete with seating and gathering spaces for students. © BIG

A high school in Hellerup, Denmark, has recently completed the installation of a sunken gym topped with a curved timber roof designed to give students a wooden hilltop to enjoy.

September 10, 2013—Sites with little room to spare are typical in Europe, particularly in urban and suburban areas. Such is the case at the Gammel Hellerup Gymnasium, a 1950s-era yellow-brick high school complex in the suburb of Hellerup, just north of Copenhagen (København). Here a large multipurpose room that will be used both as a gymnasium and as a place for such events as graduation ceremonies had to be added within the existing school grounds, which are just a few blocks from the waterfront and bounded on each side by homes. The solution settled upon by the design team was to embed the new gymnasium beneath the school’s narrow central courtyard and then add back usable space by giving the gymnasium a curved roof with a wooden surface that would serve as a plaza with seating and gathering spaces for students.

The school complex comprises three main buildings connected at the corners to form a U around a central plaza; two smaller buildings form the fourth edge of the plaza. The 50-million DKr (U.S.$9-million), 1,100 m2 concrete gymnasium has been placed 5 m underground in the center of the plaza. A second project, currently under construction, will create an arts and administration building along one side of the courtyard, replacing a building that previously housed two small gyms.

The roofline of the underground gym is created with curved laminated wooden beams in which the laminae are glued together, while the exterior has been finished with untreated oak timbers. Finn Nørkjær, the partner in charge of the project for the Copenhagen-based Bjarke Ingels Group, the project’s architect, explained in written answers to questions posed by Civil Engineering online how the curve of the roof was determined. The curve follows the trajectory of a thrown ball, he says, as defined by the mathematical formula that defines a ballistic arc. 

Exterior rendering of school complex, which is composed of three main buildings connected at the corners to form a 'U' shape around a central plaza

The school complex is composed of three main buildings
connected at the corners to form a “U” shape around a central
plaza where the new gym is located; two smaller buildings form
the fourth edge of the plaza. The upper edge of the gym’s roof
has been carefully planned so that it doubles as a bench. © BIG

The equation was selected by the Bjarke Ingels Group’s founder, Bjarke Ingels, as a way of paying tribute to one of his math teachers at the school, which he attended more than 20 years ago. The curved roofline has the added benefit of maximizing the interior space available for sports.

The new structure had to lend itself to a variety of events, and “it proved difficult to find a location for such a multifunctional hall that didn’t involve razing existing football fields,” Nørkjær said. “As a result, the project was twofold: instead of placing the hall outside the school and spreading the social life further, we created one roof serving two functions.” This would enable the interior hall to coexist with the exterior gathering spaces and would preserve the sight lines from the existing buildings across the internal courtyard.

The location of the gym and the materials chosen for its construction “ensure a good indoor climate [and] low environmental impact,” Nørkjær said. Skylights integrated into the continuous timber bench that edges the roof on the exterior and provides seating for the plaza admit daylight to the interior of the gymnasium.

Interior rendering of the ceiling of the underground gym, which is created with exposed, curved glue-laminated beams

The ceiling of the underground gym is created with exposed,
curved glue-laminated beams that have been shaped using the
formula for a ballistic arc or a thrown ball. A sheet piling system
reinforced with steel beams and additional supports has been
used for the walls, which are finished in concrete. © BIG

Excavation and construction at the site encountered groundwater conditions that were more complicated than the team anticipated, and the discovery of large granite boulders did nothing to improve matters, according to Anders Ring Petersen, the project manager for Grontmij A/S, of Glostrup, Denmark, which represented the client during the project, conducted the sustainability design work for the project, and provided engineering design support for the architects.

A solution had to be devised once the groundwater and boulders were unearthed, Peterson says. The approach involved lining the excavated pit with a sheetpiling system, as initially planned, but then reinforcing it with simple steel beams and additional supports in areas at which the sheetpiling could not be sunk to the required depth of 9 m, Petersen explains.

Three underground entrances have been created to provide access to each of the main buildings, including the replacement structure that will provide space for arts and administration. A fourth exit offers access to the courtyard via a stairwell that has been topped with a grass-covered “hilltop.”  

Energy for the project is obtained from renewable sources. Two types of solar systems are supplemented by an underground geothermal system, explains Petersen. Solar cells that generate electricity and solar panels for heating water have been placed on the existing school building roofs, and a geothermal system has been buried beneath the school’s sports field, Petersen says. The geothermal system, which offers heating in the winter and cooling in the summer, was built by laying pipes on the field and then covering the area with the soil excavated for the underground gym, Petersen says. In this manner the ground was raised approximately 1.5 m, he says.

Another exterior view of the gym, showing it being sunk far enough into the ground that the sight lines from the buildings surrounding the courtyard are preserved

The gym has been sunk far enough into the ground so that sight
lines from the buildings surrounding the courtyard are preserved.
The edge of the gym’s timber roof includes skylights hidden
beneath the bench seating. © BIG

The sustainable elements will also provide data that will have a pedagogical use. A computerized building management system located in a mechanical room logs data pertaining to, for example, temperature, the energy generated by the various systems, the amount of energy consumed at the site, and the amount of electricity sold back to the grid. Teachers will therefore be able to incorporate this information into math and physics lessons, Petersen says.

The design team also created permanent seating areas for the reimagined courtyard. White enameled steel tables and chairs, along with the circular bench along the edge of the roof are all part of the new hilltop’s landscape. The seating is backlit at night, providing the only exterior lighting in the plaza.

CG Jensen A/S, of Glostrup, Denmark, was the contractor for the project, and Copenhagen-based EKJ performed additional engineering work.

The new, 1,400 m2 arts and administration building is currently under construction. It too was designed by the Bjarke Ingels Group but is a separate project. The two-story building will have concrete walls and a sloping green roof and should be completed by next summer. While the existing buildings at the complex date to the 1950s, materials provided by the architect show that the school goes back to 1894.



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