6 Agar Street.

The major refurbishment of the offices at 6 Agar Street posed significant challenges due to the ongoing operation of a ground floor restaurant and basement gym throughout the construction process. However, using innovative engineering, we achieved an increase in commercial value for this building in London’s Covent Garden.

Location

London, UK

Client

Legal & General

Architect

Darling Associates

Project Value

£15 million

Status

completed 2012

Expertise

Structures

The building is rectangular in plan, with a central courtyard. Following a fire, the site was almost entirely rebuilt in the mid-1980s with five floors, a rooftop enclosure for plant, plus a single-storey basement. This time around, extra lettable space was added thanks to our ingenious engineering. Existing plant structures above the fifth floor were removed, to make way for a new office floor within a steel-framed mansard roof, delivering 400 m² of additional space.

Meanwhile, the floor plates on each office floor were extended 6 m into one side of the courtyard, projecting from the central lift core, augmenting the floor area by a further 600 m².

Original drawings and calculations were obtained; the objective was to identify and utilise spare load capacity within the building, while ensuring that any new loading would not exceed the capacity of the structure within the restaurant and gym, as there was no opportunity to strengthen these elements.

Initiatives included harnessing the previously untapped vertical load capacity of the concrete central lift core, originally designed to provide the building with lateral stability.

As a result, the new courtyard floor plate extensions are largely supported on existing columns via load transfer beams, with the remainder hung from a metre-deep truss that cantilevers from the top of the central lift core. Furthermore, the floor plate extensions were designed to be as minimal as possible, using a steel frame plus composite floor slabs with lightweight concrete, without compromising dynamic performance.