Building engineering and consulting

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Case study

Breathing new life into London’s Old War Office

In 2023, the Old War Office (OWO) in Westminster opened its doors to the public for the first time in nearly 120 years. Built in 1906, this iconic Grade II listed building has undergone a remarkable seven-year transformation into the UK’s first Raffles hotel and branded residences.

As the lead MEP consultant, we played a pivotal part in the conversion, undertaking the design of all MEP systems – from heating, ventilation and air conditioning to drainage and power. We also provided services in sustainability, energy, BREEAM, vertical transportation (VT) and IT/AV to support the building’s redevelopment.

Blending heritage with innovation

Turning a 1,000-room government HQ into a five-star destination was no small feat. The project added a three-storey rooftop extension and four new basement levels – now home to a spa, swimming pool, kitchens and a 600-person subterranean ballroom. Today, The OWO includes 120 luxury bedrooms and suites, nine restaurants, three bars and 85 Raffles-branded private residences.

Working closely with EPR Architects and 41 other sub-consultancies, we helped ensure the modern amenities and services stayed true to the building’s original Baroque features.

Digital coordination and sustainability

To support coordination, the entire project team used 3D BIM software containing over one million design elements.

However, on-site discoveries – such as WWII-era reinforcement beams – meant we still had to adapt and reroute services. One solution involved using an existing underground corridor to distribute building services while avoiding listed areas.

Sustainability was a core focus. The building’s high thermal mass supports energy efficiency by helping maintain stable temperatures. A state-of-the-art building management system (BMS) monitors energy use in real time. We also ensured that the building is prepared for future connection to district heating, which will further enhance its performance.