Diagonal Tower

Diagonal Tower is a 343-meter-tall office building in the Yongsan International Business District, a commercial and mixed use district planned for the center of Seoul, South Korea. The 62-story tower provides over 145,000 square meters of open office space, two double-height sky lobbies with a cafeteria and fitness center, and a penthouse executive lounge.

The project also includes two retail pavilions and a multifunctional auditorium, cubic in dimension, directly to the west of the tower. Diagonal Tower is distinctive for its rotated profile and integrated, energy-efficient enclosure. The tower commences at grade with a conventional square floor plate, which is rotated 45 degrees at one third the height of the tower and then rotated again at two thirds the height of the tower.

The resulting geometry offers varying octagonal floor plates and engages nearby landmarks. Instead of penetrating the interior of each floor plate, structural columns are integrated into the skin of the building. A megaframe carries loads diagonally along the folded edges of the tower’s faceted geometry and is supplemented by a set of vertical columns running along the facade at 12 meter spacing. The structural diagonal grid mitigates wind and seismic forces and uses 25% less steel than a conventionally framed building.

Sun shading fins, placed diagonally on each facet of the tower, vary in depth and spacing to achieve ideal shading targets. Overall, the repeating modularity of the structural and exterior wall profiles define a strikingly sculptural silhouette against the Yongsan skyline.

The ground floor lobby at the base of the tower is clad in a cable net wall, minimizing the appearance of the tower’s structural supports and creating a grand and inviting entrance to the building. The ceiling of the lobby slopes up and away from the core wall to hide the transferring columns, which allows the lobby to remain column-free with the exception of four corner piers. The piers, sloped ceiling and core walls are all clad in the same grey stone, providing the impression of monolithic stability at the base of the twer.

The building façade consists of a custom unitized curtain wall system with thermally broken aluminum framing and two-sided structurally-sealed, triple-insulated low-E glazing. Floor to ceiling glass units extend seamlessly to cover both vision and spandrel areas, and are broken only by a narrow horizontal track at each floor for the attachment of curtain-wall supported, aluminum fin shading devices.

Structural columns are integrated into the skin of the building; this effort not only creates an uninterrupted expanse of open space at each floor, but also intelligently balances the window-to-wall ratio to improve the building’s thermal performance. The tower will also be one of the first office building in Seoul to employ an integrated chilled beam cooling system.

Located to the west of the tower, a perfectly cubic 40m x 40mx 40m glass auditorium provides multifunctional space that can transform to offer a variety of spatial configurations. The exterior façade’s cable net wall system minimizes the wall’s structural members and exemplifies the concept of a pure glass volume. This concept is reinforced by the frit pattern on the glass, which not only reduces direct solar insolation, but also softens the cube into an abstract and ethereal volume, preventing it from becoming sterile and un-inviting.

An iconic solid mass is present within this ethereal glass enclosure; depending on the event within, this solid mass can open up and become transparent, offering passers-by views of the events inside. The openness on all four sides of the cube provides visual and physical connections to the Diagonal Tower, retail pavilions, and adjacent buildings.

Two small retail pavilions along the glass shaft boxes and trees of plaza landscape create neighborhood-scale spaces on the otherwise vast plazas between buildings, offering pedestrians and passers-by an attractive and friendly environment.

Description from architects.