Former IBM Pilot Head Office (now Lynx House)

Office building, 1970-1 by Foster Associates; structural engineers Anthony Hunt Associates.

STRUCTURE: a single storey pavilion with a steel frame and fully-glazed neoprene gasket wall, raised upon a mesh-reinforced concrete raft. The steel frame, designed in collaboration with Anthony Hunt Associates, is a grid of 600m welded-steel lattice girder beams at 2.4m centres bolted to square-section steel columns. The roof deck incorporates a servicing zone, with hollow columns doubling as cabling ducts.

PLAN: the deep plan, without a courtyard, was designed to be compact and hence economical. The interior is largely a single volume capable of flexible partitioning and divided down its long side by a ‘central street’ and surrounded on three sides by a perimeter walkway. In the original layout, this divided the large office zone to the south-west from smaller specialised zones (entrance lobby, reception area, staff cafeteria, computer suite and two service cores) to the north-east. This arrangement has been partially reconfigured, retaining the central spine and office zone, but with the entrance and lobby moved to the south and the other specialised functions rearranged.

EXTERIOR: the building's outward appearance is of a long, low rectangular box, entirely sheathed in 4×2m tinted glass panels. A small number of the original panels have been replaced. The latter, manufactured by Pilkington, are held in place by black neoprene gaskets fixed into aluminium box-section glazing frames. These, and the internal structure of steel columns and lattice beams (originally painted yellow-brown), are clearly visible through the glass. The full-height mullions are supported on steel angles bolted to the concrete raft. The external elevations are punctuated by pairs of doors, of tinted glass set in frames of black anodised aluminium.

The main external alteration has been the addition, in the middle of the south-east elevation, of an entrance ‘portico’ with a Portland stone surround and a glass ‘pediment’; this is not of special interest. The rear wall of the porch forms part of the listed glazed wall. On the roof are mounted air-handling units, railings and CCTV cameras; the rooftop plant and fixtures are not included in the listing.

INTERIOR: the glazed perimeter wall is the main visual focus; the regular rhythm of full-height mullions in counterpoint with the more widely-spaced steel columns. Other internal finishes, including floor surfaces, suspended ceilings, partitions and furnishings, are largely or entirely later replacements. Above the suspended ceiling is a service zone. With the exception of the structural members, the interior* is not of special interest..

• Pursuant to s.1 (5A) of the Planning (Listed Buildings and Conservation Areas) Act 1990 (‘the Act’) it is declared that these aforementioned features are not of special architectural or historic interest.