Façade Consultant: Arup
Client: Channel 4
Architect: Richard Rogers and Partners
Façade Contractor: Octatube
The Refurbishment of a Grade II-listed Cable Net Façade
The iconic building of Channel 4 Headquarters in London, originally designed by Richard Rogers in the 1990s, is Grade II-listed with only a few of its kind around the world. It reflects an era of ‘design by testing’ where boundaries were pushed and technical excellence was defined. The result is a highly engineered 20-metre-high curved curtain wall façade that combines ground-breaking features such as suspended glass panels, shock-absorbing suspension springs and a pre-tensioned cable net fixed to an ingenious steel crown. After twenty-five years, the façade was showing its age and needed care and attention.
Image credits: Octatube
Sustainable preservation
Sustainability was a unique project driver. Subsequent preliminary façade and structure condition assessments revealed that any refurbishment strategy would require specialist expertise. And while demolition followed by reconstruction was tempting, rigorous appraisal, planning and collaboration enabled a minimal carbon approach by re-using the existing cable structure, steel crown and materials wherever feasible and minimising new manufacture. Octatube and Arup were asked to preserve the high-tech appearance of the distinctive façade while updating it to meet modern (safety) standards. The result, with minimal modifications to the original design, respects and honours the building’s heritage while ensuring its longevity and continued relevance.
Image credits: Octatube
In-depth structural analysis
Meticulous research was conducted to understand the structural behaviour and condition of each façade component. This included historical research, material studies, and extensive 3D FEM analyses. Combined digital and engineering methods, such as rope-access inspections and drone surveys, were used. All data was visualized in abstracted dashboards, providing insights into the state of cable nodes and glass fittings. Expert third parties assessed the structural condition of existing geometry, cables and clamps, providing valuable insights for the design team.
Safety first
Safe dismantling was crucial, given the fact that the building was live during construction. Various elements of the façade create structural loops, making the entire façade a delicate structural interplay. An impressive scaffold was constructed to reach all areas of the façade, back-up connections were created and an additional third load path for the glass's self-weight was introduced to enhance safety during disassembly and installation of the suspended glass façade.
Cable net refurbishmentThe cables of the cable net, consisting of prestressed parabolic-shaped horizontal and vertical cables, only required cleaning. The special cable clamps with very small tolerances connecting the cables were measured, dismantled, cleaned, and refurbished, replacing parts only when necessary. Additional temporary safety clamps were installed to prevent sudden releases of energy due to wear and precision issues. The refurbishment of each node was thoroughly documented.
Image credits: Octatube
Glass upgrade
The existing 12 mm hot bent and fully tempered monolithic glass panels showed damage around the point fixings. After securing the glass panels individually with straps as a third load path, the pre-tension on cable net was reduced by 10% to safely remove the glass. Fully tempered, laminated glass panels (8.6 mm) with improved post-breakage durability were installed. A test was conducted to demonstrate the impact resistance and post breakage behaviour of this glass. An HD Light Blue 52 Guardian coating was applied to reduce solar heat gain in the atrium. Structural sealant was tested extensively as a second load-bearing path, successfully supporting the full weight of the façade glass with minimal deformations. This provides sufficient time to replace any broken panels in the future.
The project demonstrated that refurbishing complex designs is feasible and can reduce emissions. It highlighted the importance of considering refurbishment prior to an initial build to improve circularity and reduce the embodied carbon impacts of disassembly or refurbishment. These efforts enhanced the building's energy efficiency and promoted the health and well-being of its occupants. This approach ensures the longevity and continued relevance of iconic structures like the Channel 4 Television Headquarters.
Image credits: Octatube
Image credits: Octatube
Image credits: Octatube