Shonan Christ Church | TAKESHI HOSAKA architects

The curved as-cast concrete roof is a one of the striking feature of the Church, in the quiet neighbourhood, located in Shonan area where is along the coast of Sagami Bay in Kanagawa, Japan. This church provides approximately 175m2 and has single storey with RC structure. Arup was consulted about structure and lighting environment .

Associate with the hexameron in the Creation of Genesis, the architect, Hosaka Takeshi was inspired and designed the “six” roofs.
The characteristic 6 curved slab is designed not only architectural reason but also it provides structural, acoustic, and lighting benefits.
By steric effect from their curvature, the roof can span 7.6m length only with 250mm thickness and in each curved slabs, there’re void tube which reduces the weight of the structure. In the case of the seismic, especially their spanning direction, the shear wall with 300mm thickness and the curved slabs behaves as if moment frame structure since the girder slab has stiffness for the direction.
The both side of each roof, there’re gaps in order to taken in natural sunlight. They brighten the space of chapel with daylighting and it secures sufficient supply of illuminance. Therefore, the daylight from the opening is enough to be able to fill the space with bright natural light during the daytime. The opening is also designed to avoid the direct sunlight during the time of worship.
The curves provide us to avoid intensive the sound of carol and sermons.
Having curvature, the sunlight reflects spreads into the room and it is blighter than the case of flat slab. Even the moonlight falls to the inside and leads us to fantastic world.

Among the acoustical design requirements for the sanctuary, a focus was made on ensuring that the congregation would be able to hear the sermons clearly. To this end, the reverberation of the space was limited to an appropriate level and measures were taken to inhibit the occurrence of undesirable echoes.

Architecturally, the sanctuary’s ceiling was planned to be the exposed underside of the building’s curved concrete roof. From an acoustical design perspective, this curved shape provides abundant early sound reflections to the sanctuary uniformly. On the other hand, since the side walls of the sanctuary were designed to be parallel, smooth concrete surfaces could result in undesirable echoes. Furthermore, we needed to add sound absorbing material to the side walls to avoid excessive reverberation. For both of these, a pattern of vertical ribs with a random periodicity was created on the concrete side walls. And between the ribs, strips of sound absorbing black urethane foam were inserted. In the sanctuary, the pastor's speech could be heard clearly and easily throughout the space, while the hymns could be heard softly.