Inverted Roof Design For Southampton Oncology Unit

A STATE OF THE ART oncology unit at Southampton General Hospital has become a flagship facility for the area with an inverted roof design.

With 27 dedicated beds, cutting edge treatment rooms and medical equipment, the new oncology unit would provide life-saving treatment for cancer patients and essential support services to the locality.

With works initially scheduled to commence during the COVID-19 pandemic, the NHS Trust Estates Team worked closely with Garland UK and the contractors to speed up the construction as safely as possible to ensure the vital facilities were available as soon as possible.

From the outset, Southampton General clearly outlined its future intentions to increase the capacity of the oncology unit and fully utilise the inverted roof design by adding extra stories of ward space.

Inverted Roof Design

As an essential part of Garland’s brief, the unique design intentions for the building’s upward extension had to be considered, and the rooftop waterproofing system required careful planning. Garland Technical Manager, Paul Boole and Technical Assistant, James Hiscock, worked closely with the building designers and surveying firm to design a high-performance roof system that could be easily removed when the time came to increase the ward’s capacity.

Paul said, “The solution for this project required all parties to think differently. The hospital had plans to extend upwards in the future; however, a temporary roof system would not necessarily provide the best waterproofing coverage. In addition, as part of the design, Southampton General wished to include a photovoltaic system that could be used straight away and be re-used for the roof extension in years to come.”

After thoughtful consideration, the facilities management team selected an inverted roof for high-performance waterproofing whilst allowing straightforward access and maintenance. The easy access points would, in turn, be beneficial for maintaining the photovoltaic system in the future.

Bituminous Membrane System

Approved Contractor, Warner Contracting was assigned to the project, and once the new concrete deck had cured, installed Garland’s high-performance bituminous membrane system. Using the StressPly Evolution fully bonded underlay and StressPly Flex cap sheet, the tailored system included 200mm of XPS thermal insulation to achieve the required 0.15W/m²K thermal performance for a new build construction. Finally, over 100 tonnes of ballast was hoisted onto the 900m​² roof, providing a secure platform for the PV system and access walkways.

Warner Contracting also constructed plywood parapet upstands to cover the building’s steel frame and built to a height that meant a perimeter safety handrail was not required. The plywood upstands would not allow for an open flame, torch-on product, so they were encapsulated using Garland’s self-adhesive StressPly Flex SA, conforming to Safe2Torch guidance as outlined by the NFRC.

With careful design and planning, Southampton General Hospital now has a watertight and durable roof system that can be easily renovated for the additional stories in the years to come.

Completing the project in just six months and within budget despite the restrictions of the COVID-19 pandemic, the NHS Trust were delighted with the final result. With its doors open and fully operational, Southampton General can support more patients than ever before, providing a comfortable and spacious environment to receive potentially life-saving treatments and personalised care.

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