The atrium is at the heart of the complex, with overlooking office spaces. The Debis Tower stair, with the double envelope in open summer position in the foreground, clearly shows the maintenance platforms within the double envelope and grates which offer sun control. Photos: Gianni Berengo Gardin

Project: Debis Tower, Postdamer Platz, Berlin, Germany

Owner and Client: Daimler-Chrysler AG

Architect: Renzo Piano Building Workshop

Engineers: IGH/Ove Arup & Partners
Schmidt-Reuter & Partner (HVAC)
IBB Burrer, Ove Arup & Partners (Electrical Engineering)

Natural Ventilation


Typical Glazing Properties:
insulating low-E glass

Double Envelope Glazing Properties:
insulating low-E glass

Debis Tower

Buildings are static objects. While they are fixed in space, the sun is in constant motion throughout the day and year. Many daylighting strategies do not account for the sun's motion, but some address it brilliantly, allowing building occupants to control and tune their environment. Berlin's Debis Tower is an example of a building using operable elements to supplement the basic design decisions that support good daylighting.

The attitude that occupants should have a high degree of control over their environment with an operable, layered facade impacted building development and detailing. Codes and site also shaped form. For instance, German building regulations mandate that all office workers must be less than 25 feet from a window and natural light. This norm impacts building form, giving rise to the atrium. Debis's important site, Potsdamer Platz, the historic center of Berlin—meant that urbanistic concerns had to be addressed. It was critical to maintain the traditional street edge and take cues from the city fabric. Debis Tower is essentially a full city block, with a center atrium hollowed out of building mass to provide light and fresh air.

Exterior of the Debis Tower at street level. Six- and seven-story low-rise buildings in foreground, with twenty-story tower beyond. Photo: Enrico Cano

Debis's office spaces, totaling 482,000 square feet, sare within relatively thin building volumes accessible to light and fresh air. Throughout the complex, occupants can open their windows for ventilation. External aluminum sun blinds, which the occupant controls electronically from the interior, control light and glare on all exterior facades. Beyond this, the complex's twenty-story tower proper, the adjacent, lower six- and seven-story buildings and the spaces fronting the six-story atrium employ different key environmental control measures:

  • On the tower's east, south and west elevations—which have high solar gains—an outer layer of glass panels sits 27 inches outside the inner wall of operable glass windows. The panels, controlled by sensors, pivot open in summer. In the closed position in winter, they offer thermal protection. Along with the external blinds, maintenance platforms within the double envelope function as horizontal sunshades.
  • Within the complex's lower buildings—six and seven stories—the outer wall of pivoting glass panels is replaced by fixed terra cotta rods, which act as a sunscreen. These elements cut off high sun angles, supplementing the operable external sun blinds just outside the window.
  • If blocking or tuning light with operable blinds is the external facade strategy, the atrium is about filtering. Fritted glass fins diffuse and temper light entering the skylight. Windows overlooking the atrium receive fritted fins with glare control curtains used also on the office windows.

Double envelope of the tower with operable window inside, and an outer glazed skin. In this photo, the outer skin is open in the summer position. Photo: Colt International

Maximizing building surface area is one response to designing for daylighting, with the corollary that sun control is also necessary. At Debis, glare and other light control issues are addressed within a building envelope featuring substantial user control. The tower's double envelope and the layered facade on the lower buildings also addresses thermal and ventilation issues, resolved in a sustainable manner with occupant control.

This is especially important in the tower proper, with its high internal gains. The double facade's summer and winter modes are just the start to thermal control measures. For instance, the upper light opens automatically at night when the weather is warm enough to flush out the heat accumulated during the day. The concrete floor slab is exposed at floor perimeter to radiate out heat accumulated during the day. These measures, along with the combination of shading and double wall, reduce heat loads to make air-conditioning supplementary.

A detail of the fritted louvers which diffuse the daylight entering the space. The windows overlooking the atrium also have fritted louvers to temper the light. The frit density decreases on the lower level windows, to let in more light. Photo: Gianni Berengo Gardin

The project is clad in a very elaborate, maintenance-intensive curtain wall that, along with other energy-efficient, sustainable measures, is projected to reduce primary energy consumption by 50% compared to normally air-conditioned offices. With the opportunity to control light and ventilation, occupants can control their environment in a way not possible in sealed, air-conditioned buildings.


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