Portcullis House provides much-needed new offices for 210 members of parliament (MPs) on a highly sensitive site opposite the Houses of Parliament.

Located alongside Norman Shaw’s Grade I listed Scotland Yard building, the ultra-low energy offices are designed to complement the UNESCO World Heritage site setting.

Conceived in the tradition of historic Thames-side palaces, the offices are organised in a six-storey rectangular block around a central atrium. This is covered at second floor level by a frameless glass skin supported by a spectacular oak and stainless steel diagrid. Surrounded by cafes and a library and a two-storey cloister, the atrium is designed as the social focus for Parlimentary life, and is linked to the Palace of Westminster by a secure underpass.

On the ground floor, an open arcade extends along the two street frontages. Publicly-accessible Select Committee Rooms are located on the first floor, served by the upper level of the cloister. Five floors of offices for MPs and their support staff are located above, with offices on recessed attic levels including balconies onto the atrium or bay windows onto the outside.

Perimeter walls are formed in sandstone piers flanked by bronze clad ducts. At the top of these, welded bronze and steel box girders, doubling as air ducts, form spider-like roof frames topped by an array of 14 distinctive chimneys. These act as terminals of a sophisticated, energy-efficient ventilation system. Inside the building, solid oak is the dominant material for the interior linings, fittings and furnishings.

The building’s structure was informed by the presence of Westminster Underground Station below, which our practice also designed. While the outer walls could be supported on a continuous substructure, there were only six possible points to support the inner courtyard walls, leading to the use of six massive columns tied by a transfer structure of concrete arches.

The building received a BREEAM Excellent rating, the highest available at the time of its completion, with energy use reduced to between a quarter and a third of a conventional urban building of this size.