Construction (1969 –1972)
At the end of the 1960s Chase Manhattan Bank appointed Frankfurt architects Meid and Romeick to design an office building at Taunusanlage 11. The solitary 75 meter tower created a distinctive landmark in Frankfurt’s high-rise cityscape. In the most American city in Germany, the architects looked to the Seagram Building in New York (1958) for inspiration. Like its American cousin T 11 towered over a small plaza, was aligned with neighbouring buildings, had horizontal bands of glazing with vertical profiles, and spandrel panels clad in dark metal. The tower was crowned by a rooftop plant enclosure. Chase Manhattan was the sole user and had the interiors designed in the style of an American open plan office. The building was fully air conditioned.
First renovation (1992 –1994)
In 1990 the building was sold to a new owner, who appointed KSP Engel Kraemer Schmie-decke Zimmermann to carry out renovations and to divide the building into 30 rental units, but this was revised when a legal firm was secured as the main tenant. T 11 became the most expensive office space in the Main metropolis. A significant factor in the building’s high rental value was the transformation of the lower levels. The forecourt was raised up a few steps and a new ground floor entrance created with conference rooms behind. The plinth level was given a two storey glazed facade, which was carried through in the new two storey extension.
These changes gave the tower a more balanced proportionality. The spandrel panels and transparent glazing considerably brightened up the facades, and the rooftop was updated with new lightweight metal cladding, which was illuminated at night. Internal changes focussed mainly on layout, fire protection and safety, and any issues affecting the rentability. A structural survey identified some serious defects; all the entrance lobby columns had insufficient reinforcement. The steel ties were missing completely, making it impossible to establish the columns’ load bearing capacity. This was rectified through a complicated process. Continuous tenant access had to be maintained on four office floors during the renovation works. The building- and media services were refurbished, but the existing air conditioning was maintained. The open plan offices gave way to cellular offices, and to improve daylight, office walls were glazed along the top and where they met the facade.
Second renovation (2011–2014)
Two decades later, again due to a change of owner, T 11 had its second and this time more thorough renovation, once again by KSP Jürgen Engel Architects. The tower was stripped back to its structural frame, and the usable floor area was increased. The new owner secured a legal firm as tenant for 80 % of the rental space and only four floors were rented to others. Renovation held several advantages over a complete new build. Firstly, retaining the structure meant a much shorter construction period, and there were also advantages in terms of planning permits: Even though it was 75 meters tall, T 11 only had to comply with requirements for a 60 meter tower; due to its sophisticated fire safety strategy, full sprinkler coverage and an escape stairs with pressurised ventilation, a second escape stairs (normally required over 60 meters) was not required. The architects’ schematics showed that the client’s requirements in terms of building services, media and IT, and flexibility could be achieved if the existing building were completely refurbished, and the proposed modern aesthetic also appealed to the new tenants. In some respects a renovated building is just as good as a new build. Taking the existing core layout, the architects reorganised the office plan, tailored to the tenants’ needs. The new 125 cm grid allowed the floor area to be optimised at 610 m² per typical office floor.
Most offices open onto wide corridors which run the full width of the building, east to west. In a fire, windows at either end of the corridors open to provide ventilation, and the views and daylight penetration help with orientation and create a bright impression.
The entrance from Taunusanlage, and the building head were also completely remodelled. The walls and floor of the main ground floor reception and conference rooms, and the first floor library were all clad in large sheets of Persian limestone. The changes on the 16th floor are more dramatic still: Where previously this was all plant area, now the space has been transformed into an open “Skylobby” with conference areas, all with panoramic views of the Frankfurt skyline. A new steel staircase leads from the 15th floor to the top of the tower, which has been completely reconstructed. To minimise dead load the engineers selected an F90 fire resistant steel frame with concrete floor slabs. All building plant now fits into the funnel shaped space whose underside forms sloping ceilings on the 15th floor. Externally the building head was also completely transformed. The metal cladding was replaced by 7,5 meter glazed facades which are illuminated by night.
Reconfiguration of the plant levels was made possible by the installation of smaller more efficient building systems, which in turn was possible due to new highly efficient facades, with insulated metal spandrel panels and quadruple glazed box windows. The 25 cm deep box windows consist of an external impact glass, a sun shade in the cavity (which can be manually controlled from each office), and a triple thermal glazed inner leaf. The original facade layout was maintained in principle but with subtle modifications: Six box windows make up each horizontal band of glazing, and three bands, framed by the four main structural columns, make up the facade width.
Previously the main columns ended below plant level, but now they extend the full building height, more clearly expressing its volume. The projecting box windows and metal profiles accentuate the vertical emphasis. The new owner wanted T 11 to achieve a DGNB Silver certification. At this stage the pre-certificate has been granted. Even though the building can be naturally ventilated through the windows, the internal climate is controlled mainly by floor convectors combined with heating and cooling ceilings.
The interiors are remarkably simple and visually restrained. Workstations have standing lamps, and cables are hidden in a service floor. Most offices have 14 m² per person. As in the first renovation, office partitions are joined to the facade by glass fins. Ceilings were made as high as possible; 2,5 m in the offices, 2,7 m to 3,0 m on the 15th floor. To allow easy access to services the corridor ceilings were divided into two sections; a solid strip along the building core and removable metal panels along the office walls. The architects were also hired to design the tenants office fit out, and with white solid-surface sheeting, Persian limestone, and only a few colour accents, they designed a range of furniture in timeless style.
The development cycle of T 11 demonstrates how the high quality revitalisation of a building like this will benefit Frankfurt’s banking district for many years to come.
