Series
•How we made it: The Delft
The project
Situated on the south bank of the Thames, neighbouring Southwark Cathedral and The Golden Hind, Minerva House is undergoing significant refurbishment and extension to become The Delft, providing 140,000 sqft of workspace accommodation with cascading terraces.
Prioritising low-carbon strategies, the original 1980s reinforced concrete frame and existing façade are retained and extended, with three additional storeys and over 50% increase in floor space, combined with new walking routes and a feature double-height entrance.
- Location: Southwark, London
- Client: GPE
- Architect: Ben Adams Architects & John Robertson Architects
- Size: 18,781 m2
- Stage: On site
- Time Frame: 2014-2027
The process
Maximising retention:
Working with the ‘bones’ of the existing building, the project retains 75% of the original structure, by volume. Using archive information and investigations we created a detailed structural model at an early stage of the project, which enabled the design team to fully understand the existing building and allowed us to maximise retention of existing structure.
Adapting and extending:
We create space and improve the building by adapting the existing structure in several ways; extending the floorplates laterally at every level to increase the commercial space, reconfiguring the existing cores to improve internal circulation, changing the use of the existing basement to create new office space and cycle storage, and constructing a rooftop extension to provide additional accommodation for future tenants, plant rooms and viewing terraces.
Additional strength and load:
By careful investigations and detailed analysis of the existing frame, we managed to justify significant load increases on the existing superstructure and foundations, with minimal strengthening works. Existing under-reamed piles were justified for an increase in loading of up to 45%, while supplementary piles were added under the extended core to accommodate the increase in massing.
Post-tensioned slab design:
The Delft is one of the first projects in the UK which uses post-tensioned concrete construction to extend existing reinforced concrete slabs. Post-tensioned concrete is one of the most efficient and sustainable types of concrete construction, using 15% less concrete and up to 40% less steel than an equivalent traditional reinforced concrete flat slab.
Site serviced by river:
The narrow street access and historically sensitive neighbouring buildings mean that access to the site by road is extremely limited for construction traffic. In an unusual solution, something not seen in London for some decades, the site is being serviced by barge via a pontoon on the Thames embankment. During demolition works, over 65% of waste from site was transferred away by barge, significantly reducing the impact on the neighbouring road infrastructure.
“This is a project we’ve been working on for over ten years, we started working on it for Great Portland Estates in 2014 and it’s evolved a lot during that time.
The building itself is highly sustainable with 75% of the existing structure and 50% of the façade retained. The structural embodied carbon is projected to fall well within LETI 2030 commercial targets when the project completes in 2027, which is quite remarkable for an office building.”
Mark Tillett, Director
The impact
Set to complete in 2027, the sensitive refurbishment of Minerva House will create a new, contemporary workplace on London’s South Bank, with new pedestrian routes and public realm linking Southwark Cathedral and The Golden Hind along the Thames Path.
The redevelopment increases the overall commercial floorspace by over 50% while retaining 75% of the existing structure and 50% of the façade. Materials removed from the deconstructed building are prioritised for reuse on site, such as the raised access floors.
The Delft is targeting a BREEAM Outstanding certification and is set to complete with a structural embodied carbon below the LETI 2030 target limit for commercial offices.
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