Holbein Gardens
Project summary: Refurbishment and 1 storey extension of a 1980s office building
Location: Sloane Square, London
Key information
Project type: Commercial
Size: 2363 sq m
Completion: 2022
Stakeholders involved:
- Grosvenor Property UK (developer)
- Barr Gazetas (architect)
- Heyne Tillett Steel (structural engineer)
- Blenheim House (main contractor)
- TFT (sustainability consultant)
- Leslie Clark (cost consultant)
- Cleveland Steel and Tubes (CST) (steel supplier, stockholder, and fabricator)
- Keltbray (demolition contactor at the Bermondsey site)
Project description
- This project is a redevelopment and one-storey extension of a 1980s office building off Sloane Square in Belgravia, creating a 25,000 sq ft modern workplace.
- The building underwent a 25% area uplift and upward extension, requiring approximately 70 tonnes of steelwork. Around 35% of the total designed steel was reused in this project, that is 24 tonnes of reused steel. This is one of the earliest projects with steel reuse in the UK conducted recently.
- Nine tonnes were reclaimed from a nearby demolition site within Grosvenor’s portfolio: Biscuit Factory in Bermondsey and US Former Embassy. Additional 15 tonnes of reused steelwork was sourced by Cleveland Steel and Tubes and refabricated to form the building’s rooftop extension.
- Reuse of 24 tonnes of steel resulted in 35 tonnes of carbon savings. The carbon impact of reclaimed steel after fabrication (modules A1-A5) was estimated at 0.3 kgCO2/kg, which is significantly lower than the average of 1.7 kgCO2/kg for virgin steel including fabrication.
Key drivers for steel reuse
Client target for low carbon, circular economy and sustainability solutions.
Amount of steel reused
24 tonnes
Embodied carbon savings*
35 tonnes
Business considerations
Reclaimed steel procurement route:
Nine tonnes were reclaimed from the client’s demolished buildings including:
- the Biscuit Factory in Bermondsey, and
- the client’s other buildings
Additionally, 15 tonnes were procured from stockholder CST that originated from various sources:
- Pinewood Studios, a film studio near London
- cancelled projects from a local stockist
- the former US Embassy site, where the steelwork was used for temporary works for façade retention.
Information available on reclaimed steel: The steel reclaimed from the client’s demolished buildings had a known provenance and tests, while the steel from the film set had original certification and proof tests. The steel from the local stockist was in new condition, but had no certifications. The steel from the US Embassy had original certificates and proof tests.
Quality of reclaimed steel, testing and certification:
The steel from the Bermondsey site was in good, undamaged condition, with a thin layer of paint that was easy to remove. However, traceability to bars was lost, so tests were used to validate available certifications and labels. The steel from the film set was in good condition without any coatings and with minimal attachments and holes. The steel from the local stockist had no certifications, so steel sections were tested individually. The steel from the US Embassy was in good condition with only a thin layer of paint.
Warranty issues: No warranty issues have occurred because steel was CE/UKCA marked.
Cost of reclaimed steel versus new steel: The steel purchased from the stockholder was considerably lower in cost than new steel. The steel reclaimed from the client’s demolished building was more expensive due to the cost of extraction from the old site and transportation for testing before it could be reused.
Economical implications of steel reuse: Steel reuse in this project was slightly more expensive primarily due to demolition, but very close to being cost neutral. Reserving the material early in the project led to considerable cost savings as steel prices soared in late 2021-early 2022.
Implication of steel reuse on project timelines: The reuse of steel did not affect project timelines. The project was delayed for other reasons.
Lessons learned, challenges and critical success factors
- Understanding the program implications of steel reuse and timeliness is important. The existing building was a concrete-framed building with a mansard formed out of steel members (including roof steels boxed in and concrete-encased columns). The structural engineer, HTS, explored the possibility of recovering these steel sections and incorporating them into the new building at the same site. However, this would have required recovering the steel during demolition in a controlled manner, transporting the steel sections to testing facilities, sorting, inspecting, and cleaning the steels, and then refabricating them. These processes would have taken around 6 to 8 weeks, which the program did not allow for. Therefore, the idea of reusing steel from the original site in the new building was not realised, but the recovered steel elements were reused in the client’s other projects.
- An early demolition audit is beneficial in establishing the viability of steel reuse. Steel for potential reuse at Holbein Gardens was identified at the Bermondsey Biscuit Factory, which was undergoing demolition at the time. HTS measured steel sizes and undertook visual inspections of the steelwork. Although the site had a lot of steelwork, much of it was found to be unsuitable for reuse. This included deep and castellated beams that were not suitable for the new building, some pre-1970s steel that was not covered by the standard SCI P427, trusses that were not suitable in terms of sizes, concrete encased steel that would require effort to clean and could lead to potential damage, and compositely designed steelwork. In the end, steel from a small mezzanine was found to be appropriate; they had simple bolted connections that were easy to dismantle, minimal finishes with fire protection coating that was easy to remove, and repetitive sizes of steel sections that matched exactly what was required.
- Additionally, steel from stockholder CST was sourced. At the design stage (RIBA stage 4), CST was approached regarding the availability of matching steel sections that could be incorporated into the project. Steel sections from a film set and local stockholder were selected. Later in the project, more reclaimed steel became available from the demolition contractor Careys, which originated from the former US Embassy temporary works. This steel was suitable in terms of sizes and was also incorporated into the project. However, some newly available in recent weeks was missed out.
- Steel recovery at the Bermondsey demolition site resulted in additional costs, as it had to be removed out of sequence with the demolition program. For health and safety reasons, the steel had to be supported on scaffold towers before being unbolted, which also added significant costs. Some steelwork coming from the former US Embassy site was recovered by unbolting because it was the simplest method for that particular demolition project. Typically, cutting off the steel at the ends is the most efficient way to reclaim steel. In this case, approximately 70% of the yield is usually recovered. Around 15% of the steel, in terms of weight, is typically found in the connections and is also cut off. When measuring steel during the pre-demolition audit, it is important to consider that the recovered steel will be shorter in length.
- Designing with reused steel was straightforward. The design was based on available steel sections and sizes, with smaller, more common sizes of steel targeted because larger sections were available. Having the flexibility to change steel sizes was important when more stock became available later at RIBA stage 5. Additionally, reclaimed steel from the stockholder had different steel sizes (such as European HE sections) that were not commonly specified. The steelwork was designed with mechanical fixings so it can be deconstructed at the end of life.
- Overall, specifying steel properties and model volumes rather than exact sizes and gradesfacilitated matching the reclaimed steel sections. Also, design efficiency is important: if the available reclaimed steel section is not being utilised to its full capacity, it is better to opt for virgin steel and leave the reclaimed steel to be used in other projects where it is more suitable.
- Agreeing on what the final product is going to look like is crucial. Reclaimed steelwork may have holes and marks from previous use. For instance, grinder marks will stay on the steel forever and transmit through the paint. If the steel is going to be exposed, it is necessary to reach an agreement with clients on what can be accepted. In this project, Grosvenor was happy that the material had evidence of a previous life, and some beams with existing holes were left exposed.
- In terms of fabricating steel sections, there were 350 individual components, with only four or five structural members being duplicated. This added complexity to the fabrication processes. The project also incorporated Cross-Laminated Timber (CLT), which required the removal of web stiffeners from steel sections to accommodate the timber. This resulted in additional time and labour required for fabrication.
- Getting supply chain on board and supply chain communication. Contractors could have provided inflated costs because of unfamiliarity with the process and concerns over the implications of steel reuse. To mitigate this, the stockholder CST was engaged early in the project to provide advice to the main contractor. Strong client involvement and CST championing steel reuse across the supply chain helped to drive steel reuse in this project.
This case study was compiled based on interviews with Cleveland Steel and Tubes and Heyne Tillett Steel, published data and a webinar on steel reuse presented by Heyne Tillett Steel and Cleveland Steel and Tubes.
The case study was developed as part of the DISRUPT project (Delivering Innovative Steel ReUse ProjecT).
* Carbon savings were calculated by HTS based on the EPD for reusable steel produced by EMR of 0.047 kgCO2/kg (for modules A1-A3). Together with fabrication (A1-A5), carbon impact was estimated at 0.3 kgCO2/kg in this project. This was compared with the average of 1.7 kgCO2/kg carbon impact of new steelwork including fabrication [5].
Further information
- https://www.grosvenor.com/news-insights/some-of-uk%E2%80%99s-first-salvaged-steelwork-reused-in-holbein-gardens-retrofit
- https://www.ukgbc.org/solutions/case-study-holbein-gardens/
- https://nla.london/projects/holbein-gardens
- Heyne Tillett Steel. 2022. Design for Steel Reuse – Engineer’s Perspective. [Poster]. Circular Steel, 30 June 2022, London
- Mills, R. 2022. HTS+ Re-Use of Steelwork – Holbein Gardens, October 2022. [Webinar]. [Online]. Sustainable Supply Chains – Holbein Gardens. [Accessed 21 February 2023]. Available from: https://asbp.org.uk/webinar-recording/sustainable-supply-chains-holbein
- Fishwick, R. 2022. Supplying reused steel for Holbein Gardens. [Webinar]. [Online]. Sustainable Supply Chains – Holbein Gardens. [Accessed 21 February 2023]. Available from: https://asbp.org.uk/webinar-recording/sustainable-supply-chains-holbein