The OWO: A new chapter in The Old War Office history book – Latest

The OWO: A new chapter in The Old War Office history book

The Old War Office, a Grade II* Listed building that once housed the British government, has been transformed into The OWO, a new destination host to the UK’s first Raffles Hotel - Raffles London at The OWO, 85 Raffles Residences and a collection of nine restaurants and three bars. The historic building, which was originally completed in 1906 and witnessed world-shaping events of the twentieth century including Winston Churchill's wartime leadership, has undergone a monumental transformation under the ownership of The Hinduja Group and Onex Holding.

Elliott Wood was appointed as structural and civil engineers in 2015 to undertake the adaptive reuse of the former government building. Key engineering challenges included the constricted site necessitating a top down approach, excavation of four new basement levels including large span spaces across the central courtyard to accommodate a grand ballroom and an innovative subterranean drainage solution to manage the long-term hydrostatic pressure on the underside of the new basement box.

The OWO: A new chapter in The Old War Office history book

A Building of Epic Scale

The Old War Office consists of more than 1,000 rooms linked by two-and-a-half miles of corridors. Alongside EPR Architects and more than 37 consultants, Elliott Wood has seen the building transformed through engineering interventions, including 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 two, increasing the building by 31 percent.

Gary Elliott said: “The Old War Office is a technically and logistically complex project that has required close collaboration between the design and construction teams to continually push the limits of what’s possible when working with such a historically significant building. It’s been a privilege to bring all that together on a project of this scale. We have successfully reinvented tis historic building and given it a new lease of life; it’s incredibly satisfying to know that its future is secured for generations to come.”

Temporary Works

The constricted site within the Grade II* Listed building created challenges for construction sequencing and phasing of the temporary works. Through close collaboration with Toureen and the rest of the design team Elliott Wood proposed a top-down construction process, avoiding excessive new foundation work and eliminating huge amounts of temporary works. This not only minimised impact on the historic fabric but delivered programme savings of over six months.

The OWO: A new chapter in The Old War Office history book

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.

The 26m trusses that span the courtyard provide large, clear spaces below ground to accommodate some of the world-class amenities offered - including a ballroom, spa and wellbeing, swimming pool, kitchens, bars, restaurants, plant, back of house facilities and a car park.

Innovative Subterranean Drainage Solution

Excavating a further 20m below the existing basement level to form a further four storeys of basement posed complex geotechnical and hydrological engineering challenges. Elliott Wood’s Development Infrastructure team derived an innovative subterranean drainage solution to manage the long-term hydrostatic pressure on the underside of the new basement box. This solution overcame the need to provide 36 plunge tension piles that would have otherwise been required to overcome the hydrostatic uplift.

Paul Davis, Director, said: “Removing the need for tension piles provided cost and time efficiencies on the project. The system we designed saved approximately 36 plunge tension piles that would need to have been 50m long and 900mm diameter, and therefore difficult and time consuming to install in such a congested environment.”

Subterranean Drainage Solution

Subterranean Drainage Solution

Elliott Wood is delighted to see the landmark project completed and the building adapted for the next chapter in its history. We are proud to be part of the team of contractors entrusted by client Westminster Development Services to sensitively restore and repurpose The OWO, preserving this iconic landmark for future generations to enjoy.