MERIT – Holbein Gardens, London

Sustainability and circularity are at the heart of a central London project where reclaimed steelwork made up approximately one-third of the overall steel tonnage.

Architect: Barr Gazetas
Structural engineer: Heyne Tillett Steel
Steelwork contractor: Cleveland Steel and Tubes Ltd
Client: Grosvenor
Photo: © Philip Vile

A 1980s-built four-storey commercial building, known as Holbein Gardens, has been redeveloped with the addition of a two-storey steel-framed extension and a rooftop terrace to create a modern, sustainable workplace.

According to the client, the project was committed to circularity and prioritised retention over demolition This was achieved by retaining the existing concrete frame, while the new areas of the building utilised low embodied carbon materials such as CLT floors and reclaimed products.

The scheme was one of the first to champion this level of circularity and as a result it has become Grosvenor’s flagship sustainability project and first net zero development.

“Designing with reclaimed steelwork and identifying the need to source the material has demonstrated that the process for reusing steel can be achieved within a standard procurement route,” says Heyne Tillett Steel’s Sophia Edwards.

Approximately 9t of steelwork was obtained from other Grosvenor sites in London, with the remaining 16t procured from reclaimed stock from Cleveland Steel and Tubes.

The reclaimed steel was inspected to confirm its surface condition, existing coatings were removed, before the sections were re-dimensioned and tested to establish the quality, grade and strength.

Having satisfied the tests, the steel was delivered to site and installed as new throughout the redevelopment to form the extension and an exterior green wall.

Overall, 93% of the existing structure was retained through extensive investigation and justification of the frame. This is said to have allowed for an efficient structural design, with most of the new mass being added with minimal strengthening being required.

Alterations to the frame were also minimised, with only a single column being moved, thereby avoiding the need for costly foundation strengthening works.

Achieving a BREEAM ‘Outstanding’ rating, the building is said to respond to its environment, avoiding any significant load changes to the surrounding infrastructure, which includes a Thames Water sewer and Sloane Square underground station.

The green wall and landscaping along the main elevations is also said to improve the neighbourhood aesthetic by increasing urban greening.

The project obtained an embodied carbon figure of 300kgCO₂/m², surpassing LETI targets of 500kgCO₂/m².

In summary, the judges say sustainability and circular economy were key drivers in this two-storey extension. To avoid strengthening the existing structure, a lightweight steel frame with CLT floors was used. The incorporation of re-used steel demonstrates how old sections and timber can be exposed and still work effectively together, creating a harmonious blend of materials.