20 St James Square

Quinn London successfully delivered an extensive restoration and modernisation of 20 St. James’s Square, a prestigious 69,605 sq ft Grade I listed office building in London’s West End.

The project required a careful balance of sympathetic heritage restoration and modernisation. Key restoration works included ceilings, decorative finishes, wall artwork, stone refurbishment, roof alterations, and thermal improvements to achieve an EPC-B rating. Alongside this, Quinn London delivered reinforcement of existing structural elements including underpinning and upgrading basement vaults to accommodate new M&E installations and improve overall building stability. The works included a new fourth-floor extension, a landscaped roof-terrace at fifth-floor level, and new lift access serving all floors through the middle of the floor plate, together with a fully compliant escape route.

Working alongside specialist heritage consultants Charles Cooper, we employed state-of-the-art microscopic paint analysis to accurately match original historic colours and finishes. A bespoke internal birdcage scaffold system with mobile towers provided safe access to the ornate decorative ceilings, enabling conservators to undertake restoration using approved heritage materials and traditional craftsmanship.

Following restoration, the building’s heating infrastructure was comprehensively upgraded. Modern air source heat pumps now provide heating and cooling via new ductwork discreetly installed within the existing floor voids. In total, 90% MEP systems were replaced, including the installation of air source heat pumps, underfloor heating, and NVHR ventilation, all carefully integrated within the constraints of a 200-year-old structure. Discrete fire detection was sensitively positioned to preserve decorative ceilings while delivering two hours of fire protection.

Our team faced multiple constraints throughout the project, a restricted building footprint with no on-site storage, occupied neighbouring properties, and the critical need to balance heritage preservation with comprehensive modernisation. We implemented a sophisticated scaffolding system spanning ground to fourth floor, utilising ‘just in time’ material deliveries and strategic use of basement areas and scaffold storage. A goods hoist enabled efficient material movement despite space constraints. When neighbours raised concerns about crane oversailing, we collaborated with the client and design team to redesign the steel roof structure into spliced sections, reducing crane lifts from five to one and using the external hoist to transport materials through the building’s lift shaft.

This project exemplifies our expertise in delivering complex heritage restoration projects that honour the past while creating functional, sustainable spaces for the future. Through collaborative partnerships, innovative problem-solving, and unwavering attention to detail, we transformed this Grade I listed landmark into a prestigious, modernised headquarters whilst preserving its historic character for generations to come.