Sloane Square House

Sloane Square House

Project summary: 1950s office block extension

Location: Sloane Square, London

Key information

Project type: Commercial

Size: 210 sq m

Completion: Q1 2024

Stakeholders involved:

  • Commercial Estates Group (CEG) (client)
  • Orms (architect)
  • WSP (structural engineer)
  • Cleveland Steel and Tubes (CST) (reclaimed steel supplier and stockholder)
  • Contractor (to be appointed)

Project description

  • As part of CEG’s London headquarters refurbishment, the project involves adding a two-story extension totalling 210m2 (GIA) to the existing 1950s office block built on top of Sloane Square Underground Station. A design review of the masonry structure and foundation capacity has enabled the extension to be added without new foundations or strengthening works, and a steel frame has been proposed to keep the weight down.
  • This project has achieved 100% sourcing of the steel proposed at Stage 3 from reclaimed steel obtained from existing buildings across the country. This success was made possible through collaboration with Orms (architect) to establish defined structural zones and with Cleveland Steel and Tubes (a reused steel stockholder) to continuously review and approve the proposed steel against their stocklist. The project has also facilitated the development of WSP’s in-house steel reuse matching tool for meeting project-specific requirements while providing valuable insights into the complexities of the steel reuse supply chain, which has yet to be established for mainstream commercial projects.
  • The total steel used in the extension is approximately 21,000 kg. By using 100% reclaimed steel, the upfront structural embodied carbon saving is estimated to be 60%, resulting in a significant reduction in the carbon footprint from 257 to 116 kgCO2e/m2.

Key drivers for steel reuse

  • Orms had a pre-existing relationship with Cleveland Steel and Tubes, and the client, Commercial Estates Group, were keen to push the boundaries for sustainable innovations.
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Amount of steel reused

21 tonnes

Embodied carbon savings*

30 tonnes

Business considerations

Reclaimed steel procurement route: All steel is supplied from CST.

Information available on reclaimed steel: CST provides size, steel grade and defects (if any) such as holes.

Quality of reclaimed steel,  testing and certification: Reclaimed steel from CST will be tested, CE/UKCA marked, and reprocessed, but may have minor defects such as surface imperfections (e.g., holes) that do not affect its structural performance.

Warranty issues: The bespoke steel specification is based on testing the reused steel from a qualified and insured testing agency. A steel fabricator will issue a manufacturing warranty for the reused steel, and the structural engineer provides professional indemnity assurances.

Cost of reclaimed steel versus new steel: The QS has estimated that reused to be a lower price than new steel. This reduction is to allow for additional fabrication that is required to utilise the reused steel.

Economical implications of steel reuse: Steel reuse resulted in cost savings in this project. Material cost savings were at 41%. Design costs included an extra couple of hours for the time spent on additional communications, and there was an additional £400 charge from a surveyor to take the steel measurements.  

The implication of steel reuse on project timelines: The reuse of steel in this project will result in cost savings, as some of the steel is cheaper than new, and despite the additional effort required for planning, coordinating, and iterative design.

Lessons learned, challenges and critical success factors

  • The key enabler for steel reuse is the willingness of both the client and architect to make it happen.
  • The stocklist provided by CST was updated a few times throughout the stage 3 design, with more sections becoming available and some being reserved for other projects. By using WSP’s steel reuse matching tool, the updated lists could be checked immediately to ensure that 100% steel reuse could still be achieved.
  • The design went through several iterations based on section availability. Initially, a reused section match for one of the larger transfer members could not be found. The design was adjusted to identify a suitable member to be used instead.
  • Revit integration and drawings were also part of the process.

This case study was compiled based on interviews with WSP, as part of the DISRUPT project (Delivering Innovative Steel ReUse ProjecT).

* Carbon savings were calculated based on the EPD on reusable steel by EMR.

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