Building background

		The building replacing the original 1956 city hall building, also designed by Nikken Sekkei, is ,located some 2 kilometers (1.25 miles) west of its predecessor and the city center. Sited amidst gently rolling hills and abundant greenery, the new city hall takes maximum advantage of the rich natural environment, which is eventually to be developed into a public park. As the intended centerpiece of the park, the building represents an ecologically sound architecture which, in addition to benefiting from natural light and ventilation, as well as the reuse of rainwater, is designed to become an integral part of the topography.

Structural system

The structural system of the atrium is based on a light steel framework, which defines the outside perimeter of the space with double columns; these create an in between zone taken up on each level by a bridge-like walkway. This solution provides direct and easy communication between the two sections of the building. These open "corridors," with spectacular views of the space below and the green landscape outside, can also be used by the public as galleries from which to observe varies community events that take place in the atrium.

While functioning as an effective "ecological core" and an energy-saving device, the atrium, along with the entire building, also represents one of Nikken Sekkei's best architectural achievements. Shaped through their extensive expensive, artistic sensibilities, and the technical skill of the architects led by Shoji Hayashi and Shusaku Nanseki, the Kakegawa City Hall is endowed with truly memorable qualities.

The reinterpretation of the traditional model, however, relys on the latest developments in architectural technology and operational engineering. The horizontal force within the steel frame, for example, is taken up by a series of tension cable beams under the slightly vaulted roof and the double-layered frames at the perimeter, where the structural elements could thus be reduced to slim 200 by 200 millimeter (8" x 8") H-section elements, producing thereby an appealingly light structure.

The extent of frame deflections caused by temperature variations and seismic movements has been minimized by distributing the expansion joints to three different locations and constructing the large, precision-made sash less glass walls with rubber gaskets and motorized ventilation windows in steel frames on the uppermost floor.

In order to decrease the amount of energy used for air conditioning, blocking out the sun's rays in the summer is effective. In the case of this building, an inner border area was put around the perimeter of each floor which lowers the direct effects inside of changes in temperature outside the building. In addition, the atrium has the effect of shielding the inner border area of each floor from the direct rays of the sun from the south when the sun is high while helping to illuminate the interior space. A nature hill blocks the rays of the sun as it sets in the west.