The Entopia Building (DISRUPT)

The Entopia Building

Key information

Project summary: Exemplar retrofit of a 1930s former telephone exchange

Location: Cambridge

Project type: Institutional

Size: 154 sq metres total area

Completion: Construction started in March 2021 and was completed in March 2022

Stakeholders involved:

  • Cambridge Institute for Sustainability  Leadership (CISL) (client)
  •  Cambridge Architectural  Research (structural engineer)
  •  Architype (concept architect)                
  •  3PM (project manager)
  •  ISG (main contractor)
  •  Gardiner and Theobald (cost consultants)
  •  BDP (M&E engineer, structural engineer and BREEAM/WELL consultant)
  •  Harlstone Group (fabricator and steel contractor)
  •  Cleveland Steel and Tubes (CST) (reclaimed steel stockholder and supplier)

Project description

  • The Entopia Building is the new headquarters for the Cambridge Institute for Sustainability Leadership (CISL), part of the University of Cambridge. The 1930s neo-Georgian style building is a former telephone exchange used for offices since the 1990s.
  • CISL develops leadership solutions for a sustainable economy, so it needed to lead by example when commissioning its new office base. The project incorporates the reuse of the original structure and material reuse including the reuse of: steel for the PV canopy, raised access flooring, circa 350 LED lights, carpet tiles, and the oak reception desk.
  • ISG reached out to CST inquiring about the availability of reclaimed steel for the canopy holding PV panels at the roof of the building. CST sourced steel from movie studios near London that had originally been used for running cameras and tracks used for filming a Marvel film. Additionally, steel from a local stockholder’ cancelled project was used.
  • Steel reuse resulted in approximately 2,000 kgCO2e savings. The upfront embodied carbon for the building of 487kgCO2e/m2 was mainly achieved due to the reuse of the existing structure.

Key drivers for steel reuse

  • Circular economy and low carbon solution targets by the client
  • The main contractor played a key role in suggesting the idea of steel reuse and sourcing reclaimed steel for the PV canopy
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Amount of steel reused

3.79 tonnes

Embodied carbon savings*

8 tonnes

Business considerations

Reclaimed steel procurement route: Steel for the PV canopy was procured from stockholder CST. Most steels were sourced from a film set, specifically camera rails and tracks used for filming, and some steel was sourced from a local stockholder.

Information available on reclaimed steel: CST had original test certificates for the steel.

Quality of reclaimed steel,  testing and certification: Steel from a film set was of very good quality. Steel from a cancelled project had cosmetic imperfections such as a few dents, but these did not affect its structural properties. As certificates were available, test pieces from each of the batches were tested to validate that the test results were the same as the certificates. The test results confirmed that the material properties met the specifications outlined in the certificates providing the project team with confidence that the material would perform as expected.

Warranty issues: No warranty issues have occurred because the material was CE/UKCA marked.

Cost of reclaimed steel versus new steel: The cost of reclaimed steel was lower compared to procuring new steel.

Economical implications of steel reuse: Steel reuse was cost neutral in this project. Procuring reclaimed steel did not cause additional work for fabricators.

Implication of steel reuse on project timelines: Steel reuse did not have any impact on project timelines. Additional time was added to the program due to a redesign not related to steel reuse.

Lessons learned, challenges and critical success factors

  • The role of the main contractor for steel reuse. The main contractor played a key role in identifying and developing opportunities for procuring reclaimed steel, leveraging their extensive network of suppliers and contractors from previous projects.
  • Early engagement is critical. The contractors were engaged from RIBA Stage 3 under a pre-construction services agreement, but an ideal scenario would be to involve them early on at RIBA Stage 2, to gain a more thorough understanding of the building.
  • Obtaining a second opinion on the cost estimations at RIBA Stage 1. The initial cost estimate for the project was a 25% premium, but the team agreed at stage 3 that this was unlikely. Steel reuse proved to be cost neutral. The lack of similar projects to compare with, especially on stage 1, resulted in the discrepancy in the cost estimate.
  • There were very minor design changes to accommodate the dimensions of the reclaimed steel. Steel had to be lifted in the hoist, so the structure was designed out of short sections that needed to be bolted together. The advantage of using shorter sections was that it was easier to find reclaimed steel in these lengths, as reclaimed steel typically comes in shorter lengths and the process of removing holes, attachments, and dents can further shorten steel sections.
  • Communication and the involvement of the entire supply chain were key. The stockholder had a dialogue with the steel contractor to reassure them that there would not be any additional fabrication processes, as the stockholder would handle the initial processing of the steel. The support and involvement of the entire supply chain played a critical role in this project’s success.

This case study was compiled based on conversations with ISG and Cleveland Steel and Tubes, published data and a webinar on the Entopia Building project.

This case study was developed as part of the DISRUPT project (Delivering Innovative Steel ReUse ProjecT).

Carbon savings were calculated based on the LCA of reclaimed steel by Cleveland Steel and Tubes. This includes inbound transport impact to the stockholder’s yard and excludes outbound transport impact to the construction site.

Further information

  5. Kelly, P. 2022. Reuse success stories: the Entopia Building. [Webinar]. [Online]. CISL Entopia Building – Material Learnings and Reuse. [Accessed 9 February 2023]. Available from:
  6. Fishwick, R. 2022. Supplying reused steel for the PV array. [Webinar]. [Online]. CISL Entopia Building – Material Learnings and Reuse. [Accessed 9 February 2023]. Available from:
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