The Willis Building

Office building, designed 1970-71 by Foster Associates with structural engineer Anthony Hunt, and built 1973-5.

MATERIALS Reinforced concrete frame with bronzed glass cladding and a turf covering to a flat roof, the latter with a hedge slightly set back from the perimeter.

PLAN Irregular plan with curved external wall, which follows the perimeter of the site.

EXTERIOR Four storeys, the steel-framed, recessed, fourth-storey glazed rectangular pavilion being set back from the perimeter leading to the grassed roof garden delineated at the perimeter by hedging and a service track for the maintenance crane. The structure comprises columns set at 14m centres with free-forming perimeter columns at 7m centres, and cantilevered flat plate and waffle concrete floor structures. The building is fully glazed in toughened, bronze-tinted glass, specially commissioned from Pilkington, and fully suspended from the edge of the perimeter cantilever at main roof level, above the second floor, in the form of a continuous skin. The 2m wide glazing panels are without mullions, secured at junctions between panes and at intermediate floor levels, by a pair of rectangular patch fittings. The entrance to the loading bay leads from Princess Street. The only pedestrian entrance is through revolving doors set close together, of bronzed glass in simple circular black frames, to Friars Street.

INTERIOR Designed as a whole by the architects. An 'atrium' rises through the centre of the building containing three pairs of escalators set in line, lit by a tubular metal-framed roof above. The escalators effectively divide the flexible, open-plan office space on the first and second floors into two zones. Fixed service facilities on the ground and third floors include the former swimming pool (see History above), computer and plant rooms to the ground floor and a restaurant, conferencing and presentation suite to the third floor. Four service cores contain the stairs and toilet facilities at each floor; the lifts are separately housed.

The architects designed an integrated service system, with raised floors containing continuous access panels for power and communications cabling and suspended ceilings enclosing polished aluminium channels that contain air-conditioning, ventilators, smoke detectors, and glare-free lighting by luminares fitted with parabolic reflectors. The waffle slab to the ceiling at the ground floor level is painted white. The colour scheme, floor coverings, finishes and furniture were carefully chosen by Foster Associates. The floor covering to the ground floor is of green studded rubber, and green carpet to the upper floors. Modular steel partitions enclosing service areas are in yellow.