One Great St Helen's, London EC3

JRA has refurbished and extended One Great St Helen’s, one of the practice’s early office landmarks in London’s Eastern Cluster, adjacent to the St Helen’s Conservation Area - an area which has changed dramatically over 30 years. The design team has upgraded the 4,500m² building to contemporary standards by adding two additional storeys, reconfiguring the entrance, and delivering renewed CAT A finishes throughout. JRA has also introduced a suite of new amenities and significantly enhanced the building’s sustainability performance.

While the original striking curved façade and sandstone-clad bookends have been carefully preserved, the project firmly reasserts One Great St Helen’s as a distinctive presence among the Eastern Cluster’s skyscrapers, serving as a thoughtful bridge between heritage and modernity.

JRA originally designed One Great St Helen’s as a contextual modern infill, drawing inspiration from the character of Crosby Square and the neighbouring 13th-century church of St Helen’s Bishopsgate. Completed over 25 years ago, the building was an early adopter of the newly published British Council for Offices Specification and went on to win the BCO Southeast Regional Award in 2000. Shortly after completion, it was leased to Hiscox, who occupied the premises for the next 25 years.
Since then, the surrounding area has undergone significant transformation. Crosby Square is now framed by major new developments, including 22 Bishopsgate, the Leadenhall Building, and 30 St Mary’s Axe, which together define today’s Eastern Cluster.

Amid growing competition from new workplace offerings, the brief for One St Helen’s was to create a distinctive, sustainable alternative for tenants while retaining as much of the existing building as possible. JRA’s ‘minimum intervention, maximum impact’ strategy delivers this with clarity.
Externally, the curved glazed façade on Undershaft, framed by its red sandstone bookends, has been retained, while a new winter garden and external terrace at level 10 introduce dramatic views and shared amenity space. A new plant floor has also been added at level 11.
Internally, a timber and terrazzo entrance hall provides a welcoming arrival space with areas for waiting, touchdown and informal meetings. A new ground-floor lightwell brings daylight into the lower ground floor, enabling valuable additional workspace. All office floors have been renewed with efficient exposed services and finished to CAT A, maximising space, light and flexibility.

The redesign places occupant wellbeing at its core. The new landscaped roof terrace and level-10 winter garden provide year-round indoor–outdoor amenity space, offering fresh air, daylight, and opportunities for social interaction within a dense urban environment. A new plant floor at level 11 maximises usable terrace space, and the passenger lift has been extended for improved accessibility.
Active travel is supported through high-quality end-of-trip facilities: the former basement car park has been converted into a secure cycle store with showers and lockers.
Interior comfort has been improved by removing solar and bomb-blast window films to increase daylight, and by introducing a high-efficiency Variable Refrigerant Flow (VRF) system that provides precise, zoned temperature control. Existing smoke vents have been retained to give future tenants the option of natural ventilation.

One Great St Helen’s prioritises sustainability. Retaining the existing building has saved significant carbon and its original design features, including retaining the modulation of the curtain wall and the fins between cladding panels, which reduce solar gain. Sustainable measures include upgraded MEP services, improved insulation, and the reuse of the existing raised floor. An all-electric servicing strategy, comprising air-source heat pumps and VRF systems for heating and cooling, exceeds the requirements set out in the London Plan, enabling the building to achieve a 57% improvement against the Building Regulations Part L carbon-emission target. One Great St Helen’s is predicted to achieve BREEAM Excellent certification. The refurbished building has achieved an EPC A rating.