The Walterboscomplex houses the Central Tax Office of the Netherlands. The original ensemble was built in the 1960s and consisted out of four office towers surrounded by a vast parking lot. The brief was to renovate the existing towers, add two new ones (designed by other architects) and finally link the freestanding towers by a clear circulation system and additional collective services for a staff of 3500.
The project rebalances the complex by introducing a long plinth building that stitches all towers together. It creates an inward oriented space for the central staff with facilities such as restaurants, conference rooms, a library, a sports and training centre and indoor parking facilities. In order to retain the open character of the site in the residential neighbourhood, the plinth building is designed as a sunken structure that opens up to two large underground patio gardens. The roof of the sunken building is covered with a reflecting rainwater pool that gives the grounds a natural base and extends into the green park that surrounds the complex. Since the building is completely below ground level, there are no street façades: the only architectural element to be seen from the street is the large reflecting pool with a clutch of stainless steel-clad cones rising from it. These cones introduce compelling sight lines and diagonals to the complex and bring daylight into the underground areas. Their steel skin has an ornamental relief imprint of dragons and water-spouting masks designed by the Dutch artist Rob Birza. The black textured concrete façades facing the sunken gardens make a strong frame for the green gardens. Inside the building floors, ceilings and walls are made of prefabricated polished concrete panels with imprint patterns of high-relief diamonds and low-relief spheres that incorporate technical installation components. Under the cones one finds intimate meeting spaces with zenithal light, warm wood panelling and soft and colourful textile wall coverings by Rob Birza.
The reflecting pool acts as a barrier to protect the high-security grounds from intruders. At the same time, the water forms a buffer tank used to cool the building. The public entrance to the complex is centrally located amidst this water landscape. Visitors descend towards the staff promenade along the sunken gardens, as in the cloister of a monastery. The elevator bays of the towers are located along this promenade. There is a secondary logistic route of back corridors for goods and catering that connects the loading bays, kitchens and storages without interfering with the staff’s route. A third circulation system is the infrastructure for the data systems, enormous bundles of data cables laid out in vast underground duct corridors that link the central computer building to the various office towers, the most vital element of the Tax Office operations.