Class A Fire-Rated Decking & Substructure System - Kings College Hospital

Project overview

King’s College Hospital developed a world-first rooftop garden designed to operate as an external extension of its Critical Care Unit (CCU), allowing critically ill patients access to fresh air and daylight while remaining fully connected to essential clinical services. The project transformed an unused roof area into a functional outdoor space integrated directly with the hospital’s critical care infrastructure.

The scheme incorporates a complex layout combining external decking areas with an integrated planter system, creating a therapeutic environment while maintaining full clinical functionality. The brief required a fully non-combustible, fire-rated decking substructure capable of supporting this arrangement, while accommodating extensive medical services beneath the finished deck and allowing for long-term access and maintenance.

The challenge

The project was delivered within one of London’s busiest hospitals, requiring tightly controlled access, timed deliveries, and carefully managed logistics. The restricted nature of the site meant that all installation activities needed to be carefully planned to minimise disruption to ongoing hospital operations.

Full compliance with Approved Document B was a primary requirement, ruling out combustible decking systems and necessitating a fully Class A fire-rated substructure solution. Beneath the finished surface, the roof contained extensive medical and building services, including gases, power, data, and drainage, all of which were critical to CCU operation.

The layout combined external decking with an integrated planter system, with decking installed between and around curved planter edges. This introduced additional complexity in terms of geometry, tolerances, and interface coordination, requiring a substructure capable of accommodating non-linear layouts without compromising stability or performance.

The solution

Wallbarn supplied a fully Class A fire-rated decking substructure system designed to address the access, servicing, geometry, and fire performance requirements of the scheme.

The system comprised MetalPad Ex adjustable steel pedestals, high-grade aluminium joists, and Class A rated fixings and connectors. All components were non-combustible and specified to align with the fire performance requirements of Approved Document B.

The adjustable pedestal system allowed precise height control across the roof, accommodating tolerances and enabling a consistent finished level throughout the terrace. The aluminium joist framework provided a rigid yet adaptable support structure capable of responding to the non-linear geometry created by the curved planter layout, allowing decking to be installed cleanly between planter edges without compromising system performance.

The suspended build-up created a continuous service zone beneath the deck, allowing medical gases, power, data, and drainage services to be routed safely while maintaining effective ventilation and drainage. Wallbarn provided technical input during the coordination stage, suggesting layouts and revising quotations based on updated information and corrected measurements. This ensured that, by the time materials were ordered, quantities and build-ups were accurate, helping to reduce unnecessary waste and cost through careful planning and early technical coordination.

Installation and performance

Installation was undertaken within a tightly controlled hospital environment, requiring careful coordination of access routes, delivery schedules, and on-site handling. Materials were delivered in planned sequences to suit restricted access conditions and minimise disruption to day-to-day hospital operations.

Exadeck porcelain boards were supplied in standard 1.2 m lengths and delivered on standard Euro pallets. MetalPad Ex adjustable steel pedestals were boxed and also supplied on standard Euro pallets, providing consistency in handling, storage, and movement through the hospital and up to roof level.

The modular nature of the pedestal and aluminium joist system supported efficient installation, allowing components to be positioned and adjusted incrementally as works progressed. Precise height adjustment enabled consistent finished levels to be achieved across the terrace, despite variations in the roof structure and the complexity of the overall layout.

Once installed, the suspended substructure provided a stable and durable platform for the non-combustible decking areas, with decking installed between adjacent planter elements. The Exadeck porcelain decking provides a robust walking surface with excellent resistance to scratching, wear, and staining, making it well suited to high-traffic external environments such as healthcare facilities. The clear service zone beneath the deck allows ongoing access for inspection and maintenance, while the non-combustible construction supports long-term performance within a healthcare environment.

Key performance criteria

Fire performance

The decking substructure system is fully non-combustible and achieves Class A performance in accordance with EN 13501-1, supporting compliance with Approved Document B.

Durability and robustness

The aluminium joist and steel pedestal system provides a stable and durable substructure designed for long-term external use. Exadeck porcelain decking offers high resistance to scratching, wear, and staining, and requires minimal ongoing maintenance. No specialist coatings or surface treatments are required, with routine cleaning carried out using standard recommended cleaning products.

Adjustability and level control

The adjustable pedestal system allows precise height adjustment, enabling accurate level correction across the roof and consistent finished surfaces despite variations in the underlying structure.

Service integration and access

The suspended build-up creates a continuous service zone beneath the deck, allowing medical and building services to be accommodated without restricting drainage or ventilation. Ongoing access for inspection and maintenance is maintained without the need for extensive dismantling.

Design life

The Class A fire-rated substructure system is designed for a service life in excess of 50 years when correctly specified and installed, supporting long-term performance and reduced lifecycle cost.

Outcome

The completed rooftop garden delivers a safe, durable, and fully non-combustible external environment that supports patient wellbeing while meeting the operational and regulatory requirements of a major healthcare facility.

Through early technical input and close coordination, the decking substructure solution addressed complex challenges relating to fire performance, restricted access, service integration, and long-term maintenance. The suspended system provides reliable structural support, future access to services, and confidence in ongoing performance, while accommodating a complex layout incorporating curved planter elements.

The project demonstrates how a correctly specified Class A fire-rated decking substructure can support technically demanding rooftop environments, providing a robust and adaptable solution suitable for long-term use on busy, high-traffic buildings.