The OWO, London – Projects
Hotel & Leisure
- EPR Architects
- The Hinduja Group & Onex Holding
The OWO is a complex engineering project involving the ambitious refurbishment, extension and adaptive reuse of the former Old War Office building in Whitehall into The OWO, home to the 120-room Raffles London at The OWO, 85 Raffles branded residences, nine destination restaurants and three bars. The Grade II* listed building once served as the headquarters for statesmen including Winston Churchill and was the inspiration for writer Ian Fleming to pen his James Bond spy novels.
Principal engineering interventions include a series of rooftop extensions ranging from 1 to 3 storeys, significant internal reconfiguration of the existing building and the excavation of four new basement levels beneath the existing.
Through close consultation with EPR and Heritage England, we developed structural proposals that took advantage of opportunities offered by the site to minimise impact on the existing Grade II* listed fabric.
New Basement Levels for World Class Amenities
Elliott Wood pushed the limits of what was proposed by the original architectural plan, proposing four new basement levels beneath the existing. The position of the basement was carefully chosen to maximise the potential area gain whilst balancing the technical difficulties of such a large excavation in and around a listed structure. To support the new basements, a top-down approach was taken, using concrete plunge columns to form the permanent structure and minimise the need for temporary works.
26m trusses span the courtyard to provide large, clear span spaces below ground to accommodate the facilities a luxury hotel needs to offer - including a ballroom, spa and wellbeing, swimming pool, kitchens, bars, restaurants, plant, back of house facilities and a car park. The basement excavation was circa 700,000 cubic ft and the building area increased from 580,000 sq ft to 760,000 sq ft.
Innovative Subterranean Drainage Solution
In addition to the traditional civil engineering works packages, Elliott Wood conceived an innovative solution to remove the need for tension piles that would otherwise be required to overcome the uplift created by the long term hydrostatic pressures within the London Clay.
Working closely with geotechnical specialists, a suite of testing was undertaken that provided the parameters that enabled Elliott Wood to design a permeable layer under the basement slab. This permeable layer permanently dewaters the basement slab, removing the hydrostatic pressure.
Geotechnical analysis and testing was used during negotiations with Thames Water to achieve a bespoke agreement to discharge the ground water to their sewer.
The system saved approximately 36 no. 900 diameter tension piles each 30 metres long which would have been either installed as plunge piles from the original basement level or installed at the new basement level which would have been a complex and time consuming operation.