One Leadenhall is a recently constructed 35-story skyscraper, adjacent to a historic Grade II* listed covered market located in the “Square Mile”, a name commonly used for the financial district within the City of London. The 177-metre tower comprises approximately 422,000 square feet of office space, two basements, a range of retail amenities on the ground and fourth floors and a public terrace. 

The neighbouring Grade II* listed Leadenhall Market began life as a forum in the centre of Roman London. This monument also served as part of the marathon course for the 2012 Olympic Games and was used to represent the area of London near “The Leaky Cauldron” and “Diagon Alley”, in the film “Harry Potter and the Philosopher’s Stone.” 

The original structure on the site of One Leadenhall, known as Leadenhall Court, was a seven-storey corner building developed in 1988 and was home to Royal Sun Alliance Insurance Group’s former headquarters. In 2015, Brookfield Properties, a North American subsidiary of commercial real estate firm Brookfield Property Partners, engaged the services of HDR’s building engineering services, as part of a major ambition, to provide a statuesque addition to the City of London’s iconic skyline. Initially, Brookfield Properties had considered refurbishing the existing outdated building, however decided later that an efficient contemporary tower could be built, with a key design consideration to flood the space with natural light and provide impressive views across London, to support employee wellbeing.

A Collaborative Effort

The project team includes HDR, Multiplex (construction manager), Make Architects (lead architect) and Robert Bird Group (structural engineers). HDR provided a contemporary and holistic building engineering services Design, encompassing mechanical, electrical and public Health (MEP), sustainability and resiliency, including an energy strategy, information communications technology (ICT), fire and life safety, and commissioning management services.

HDR assisted in developing the massing to optimise the building footprint within a constrained site, while maximising efficiencies and accounting for the complex logistics and design considerations. It was essential that Leadenhall Market and its nearby buildings were not disrupted by day-to-day operations whilst construction took place, encouraging a mindful and sympathetic approach, paying respect to the history of the local area.  

HDR’s engineers devised the heating, ventilation and air conditioning (HVAC) strategy. The design intent served to satisfy an increased demand for the highest quality ventilation, following the COVID-19 Pandemic. HDR implemented high–efficiency water–cooled chillers and plant rooms throughout the building, alongside vertical plant louvres for air intake. To balance MEP service distribution flexibility in tandem with efficient story heights, the floor system incorporates composite steel cellular beams, spanning clear from the central core to the perimeter. Flexibility is at the heart of the core service design, as future floor demarcations for split tenancies can be facilitated. One Leadenhall has also been designed with full power resilience through dual network supplier intakes.

Responsible Design

As the project’s sustainability assessor, HDR reviewed the carbon emission data at One Leadenhall; tracking the materials that were being transported to and from site, while supporting Brookfield Properties to achieve BREEAM Outstanding certification and then targeting the shell and core design to achieve WiredScore Platinum. These accreditations are testament to the success of the sustainability elements implemented, such as photovoltaic roof panels, high efficiency water–cooled chillers, unitised glass and aluminium façade, heat recovery air conditioning units and an extensive new metering system, designed to influence occupant usage and lower costs.  

HDR’s commissioning management team provided services for the shell and core fit out, utilising a programme with thousands of line items which are all task specific to the testing, validation and governance of the building, which in the 21st Century, is full of complexities. The sheer size and height of the structure presented challenges in terms of the MEP engineering and commissioning Management, given the high volumes of electricity, fresh air and light that serve the building. 

HDR’s commissioning management team was able to collaboratively manage issues, risks, actions and documents whilst providing an opportunity to record site observations, diary entries and safety risk assessments through utilising HDR’s internally developed commissioning management reporting portal, “Nucleus.” This software enables commissioning engineers to track the progress of works through a certification process.

A full digital twin created with Autodesk Revit, to be shared across the wider design team, aided much of HDR’s project work at One Leadenhall, alongside an enhanced 3D Revizto model. This provided HDR’s engineers with the best possible oversight and resulted in having to drill only 10 new holes on-site, demonstrating the enhancements in efficiency and accuracy when employing a digital twin. HDR also produced a digital energy twin to comply with Part L of UK Building Regulations and the prediction and assessment of operational energy.

Optimized for the Future

HDR served as Brookfield Properties’ chief technologist on this project, assisting in identifying technology requirements in relation to building operation and performance. From the project’s inception, HDR was able to take the client and the building operators on a digital journey in a collaborative effort to implement smart building technology, thus providing the client with a solution that serves as a Single Pane of Glass interface. This is a centralised interface that aggregates data, monitoring and control from multiple systems into one dashboard. Instead of juggling multiple disconnected platforms, teams gain real-time insights into all systems from a single view. The front reporting system has been fully integrated with the Building Management System, enabling managers to monitor and manage all aspects of data, make amendments and encourage mindful and responsible utility usage amongst occupants. 

HDR worked closely with One Leadenhall’s facilities managers, through holding various workshops to determine how the client aspired to customise how data would be viewed on one singular network, to provide a bespoke solution that would serve their unique requirements. The Facility Managers were given smart building data, providing insight as to where systems could be made more efficient and consequently provide savings. The building data was rolled out on a flexible system, which can be expanded to include smart building apps, thus facilitating further base build and fit-out analytics in the future.  

Much of a project’s building technology success derives from taking the client on a journey that will help to make informed data-driven decisions; while maintaining a long-term working relationship with the client well beyond project completion. HDR’s ability to manage varying disciplines on such a large scale was imperative to the project’s success and the integration of various disciplines throughout the wider project team. 

The new tall tower boasts an aesthetically pleasing glass façade and offers fantastic views across the U.K.’s capital. An almost triple-height reception and a range of brand-new retail outlets occupy the ground level within a four-story masonry “street block”, reflecting the characteristics of similarly sized neighbouring buildings. Biodiversity is also an important sustainable and wellbeing aspect of One Leadenhall, found throughout private roof terraces located on the 29th and 32nd floors and a public terrace on the fourth floor. The building also includes an adaptable space, suitable for hospitality and entertainment. The retail unit of the fourth floor features a flexible design, which can be used to house a restaurant, which will provide an elegant dining experience with enticing views across London.

Chi Chiu, Divisional Director for HDR commented: 

“HDR is proud to have contributed to One Leadenhall, an ambitious project shaped by collaboration, resilience and a shared vision. Delivering a modern landmark in London’s historic Roman quarter required adaptability, creativity and close partnership with our client, project team and industry partners. The result is a stunning building that stands proudly within the city’s iconic skyline, reflecting the dedication of everyone involved. One Leadenhall is a true testament to the Art of the Possible.”

As of early 2026, One Leadenhall is fully let, with Latham & Watkins LLP, a Global Law Firm, occupying most of the available office space, having signed a long-term tenancy on the site at the heart of the Square Mile. Digital asset company, Ripple, has taken 90,000 square feet of office space at the top of the building – while global luxury workspace provider, The Work Project (TWP), has leased 30,000 square feet of office space, across two floors, marking TWP’s entrance into the British market with its premier UK location. This elegant addition to the British Capital’s cityscape has created a fine aesthetic and ambience that allows its occupants to forever feel connected to the rich tapestry of the surrounding urban landscape. 

Images courtesy of Nick Hufton © Brookfield Properties 2026