The level of the basement was selected to be above ground water level to reduce reliance on water protection, and to allow clerestory gazing in the south and west of the site where the ground level is lower.
Structural solutions providing thin horizontal structure without downstand beams were used to achieve generous headroom. The superstructure comprised loadbearing blockwalls forming the individual rooms, supporting in-situ reinforced concrete floor slabs. At ground level over the basements, the loadbearing walls are supported by a column and beam structure to ensure ease and flexibility of internal planning. Parts of the building required a special approach, including the glass lantern which provides ventilation to the building, and the support of the sundial. The bridge entering the car park from the north is detailed and structured to minimise loading on to the avenue of plane trees, and the Master's Lodge is designed to maximise structure-free space.
Some large spaces were required at the base of the building, particularly over the Nihon Room and the large music room in the basement. To span these spaces, the cross-walls of the superstructure were designed to act compositely with the floor slabs above and below, thus forming wall beam structures spanning the full width of the building: the walls act as webs and the floor slabs act as flanges to the storey-high beams. By using this approach, obtrusive downstand beams and associated lower ceilings were avoided: a simple flat soffit was provided.
Some stairs, particularly the main stair in the Master's Lodge, were designed to have exceptionally thin waists, to have long spans, and to be separated from support from side walls. An exposed steel plate forms the soffit of the stair, acting compositely with the stair construction and hence reducing overall depth.
Mike Glover, Ove Arup & Partners