HLM Architects' office building inserted into London's Arundel Great Court has been ingeniously designed to serve as the hub of the complex – without being glaringly obvious
Arundel Great Court, Frederick Gibberd's grand courtyard complex of stone-clad office buildings erected in the 1960s between the Strand and the Thames, has been partly filled. Although invisible from the surrounding streets, a new four-storey, fully-glazed office block has been dropped into the complex to cover half of the courtyard towards the Strand frontage.

The block adds about 5000 m2 of extra office space to the complex. More importantly, it forms a central hub that unifies what had been five separate office buildings but are now wholly occupied by one company, international accountant Arthur Andersen.

The challenges facing HLM Architects and structural engineer Waterman Partnership were considerable. On the structural side, the new building had to be supported above two existing levels of underground carparking. Waterman Partnership hung the whole building off six new tubular steel columns, which required the removal of just six underground parking spaces. The new columns, 600 mm in diameter, rise through the building to appear like masts above the roof line. From the top of the masts, slender steel tension bars stretch out diagonally to support a continuous steel triangulated truss supporting the upper two floors of the block, with the first floor suspended off steel hangers at 9 m intervals.

Daylight had to be admitted to the building through narrow gaps without creating reflections that could dazzle occupants of the existing offices. So HLM designed the external skin as curtain walls of clear, frameless glazing to admit maximum daylight, but sloping outwards by eight degrees to avoid reflections.

The new building boasts a spacious atrium that serves as a grand new entrance hall and circulation centre for the whole complex, with glazed passages leading off at first-floor level to the existing buildings on either side. Other than the new connections at ground and first floors, the only change to the existing buildings has been to add an imposing entrance facing the Strand. This now leads through the new circulation hall to link all five buildings of Anderson's refurbished UK headquarters.