Interspan is delighted to announce that our work on the Space House refurbishment has been awarded the CONSTRUCT Day 2024 Post-Tensioning Association Retrofit Project of the Year.

A Historic Structure Reimagined

Originally constructed in the late 1960s, Space House was engineered by Pell Frischmann and consists of two interconnected structures—Kingsway House, a 7-storey building, and the Space House tower, rising 16 storeys. Both buildings share two basement levels, creating a complex structural framework.

The challenge of revitalizing this iconic Grade II listed building lay in carefully balancing preservation with innovation. The project’s goal was ambitious: a two-storey extension to the tower while ensuring the integrity of the existing structure.

Interspan’s Role: Pushing Boundaries with Post-Tensioned Solutions

Working with the Toureen Group, Interspan’s involvement focused on constructing new slabs for levels 15 through 17. This included a 345mm thick slab at level 15, a 300mm thick post-tensioned (PT) slab at level 16, and a 350mm thick transfer slab at level 17.

Each level presented unique structural complexities, particularly due to the circular floorplates at levels 16 and 17. To address these challenges, Interspan implemented circular ducts, ensuring the post-tensioned tendons followed the building’s geometry without causing undue friction losses. The sequence of tendon stressing was carefully planned to prevent locking individual strands, ensuring a smooth and efficient tensioning process.

For the level 15 infill slab, the connection to the existing concrete was designed as a pinned joint, allowing for controlled movement between the old and new structures. To manage the differential shrinkage strain between the slabs and avoid cracking, we incorporated sleeved dowel bars at 300mm intervals, grouted after 56 days to ensure the new slab bonded seamlessly with the existing structure.

Pioneering Techniques for Structural Integrity

An innovative feature of the design was the inclusion of a perimeter pour strip on all levels. This strip served two key purposes: isolating the slabs from the existing façade to allow for initial drying shrinkage and providing edge-stressing access, which was critical for ensuring the long-term stability of the slabs.

A Modern Marvel in London’s Skyline

Space House is a shining example of how modern engineering can harmoniously blend with historical architecture. By combining cutting-edge post-tensioning solutions with meticulous planning and execution, Interspan has contributed to both the structural integrity and aesthetic beauty of this iconic building.

The result is not just a structural achievement but a visual one—a symbol of sustainable, efficient, and aesthetically compelling construction in the heart of London.

Space House stands as a testament to the future of retrofit engineering, where history and innovation come together to create something truly extraordinary.

Image Credit: Savills

More Info: spacehouse.london