Transforming foundations at Keybridge House with Clayboard

The Clayboard Keybridge House project is a prime example of how a bespoke void forming solution supported regeneration in challenging urban environments. As part of a £50 million redevelopment in London’s Vauxhall district, Clayboard was chosen to deliver load separation above existing foundations with speed, sustainability, and certainty. Designed for use as a compressible void former, the Clayboard system helped create a controlled void beneath deep transfer beams, preventing stress on the original concrete slab below and enabling the transformation of a once ‘brutalist’ building into a vibrant mixed-use space.

Clayboard Keybridge House: Reimagining load management in urban groundworks

Located on the site of a former BT telephone exchange, Keybridge House had long dominated the Vauxhall skyline. But the old structure wasn’t without merit, particularly its solid concrete foundation. Rather than demolish everything, engineers opted for a transfer structure, using deep beams to shift the load of the new development off the existing base.

Enter Clayboard, a smart, lightweight solution designed to sit beneath suspended slabs or transfer beams and create a permanent void. With no ground heave to accommodate, the goal here was void protection: controlling compression during and after the concrete pour, then allowing Clayboard to give way once the concrete reached self-supporting strength.

Want to understand more about how void formers like this work? Read our blog: What is a void former used for?

Why choose a compressible void former?

When working with complex loads, restricted access, or environmentally sensitive sites, a compressible void former like Clayboard provide a flexible and cost-effective alternative to rigid systems. If you’re aiming to reduce excavation, speed up installs, and cut embodied carbon, collapsible solutions are often the smarter route.

Want to explore the full picture? Read our in-depth blog: Is it better to use compressible void formers?

Bespoke void forming solution for non-standard beam depths

A key complexity in this project was the non-standard beam depth of 1500mm. This required custom-sized Voidpak irrigation systems and tailored Clayboard panels, a task made easier thanks to Clayboard’s modular design and UK manufacturing. With input from O’Halloran & O’Brien and SIG South Ruislip, Dufaylite provided a full design-to-delivery solution, quickly turning around a specification that fitted the exact layout of the slab. Installation benefits included:

• Thinner profile than traditional polystyrene void formers, so less muck-away
• Lightweight panels made handling and site logistics easier
• Precise collapse enabled via Voidpack water introduction
• No uplift resistance after collapse, reducing steel reinforcement needs
• Recycled core aligned with sustainability goals

Sustainable and smart ground heave technology

Even though this project wasn’t dealing with ground heave, many of the same advantages of Clayboard’s ground heave system applied:

• Made from 100% recycled, recyclable paper
• 30% thinner than traditional void formers
• Reduces over-engineering risks with no complex fail load calculations
• Certified by the British Board of Agrément (98/3528)
• Suits urban regeneration projects with low-carbon targets

Key benefits of Clayboard for urban projects

• 30% thinner than EPS alternatives, resulting in less excavation
• Easy Voidpack water activation without complex engineering
• 100% recycled, recyclable paper honeycomb
• Certified BBA performance assurance
• Ideal for use with transfer beams, slabs, or podium decks

Used globally for smart structural separation

While Clayboard is primarily used across the UK, it’s trusted internationally in a wide range of ground separation applications. Beyond Keybridge House, Clayboard has been used to protect:

• A live subway tunnel in Brooklyn, NY
• A power station in Sudan
• A car park constructed over a tunnel in Gibraltar
• A high-profile bridge deck for the Queensferry Crossing in Scotland
 → Read that case study here

Wherever controlled collapse and long-term durability are required, Clayboard delivers.

Let’s talk void formers that work

Whether you’re working on a new build, redevelopment, or complex retrofit, our team is here to help you integrate smarter, lighter, and more sustainable solutions into your design.

Contact our team today to find out how Clayboard could support your next urban construction project.

If you’re planning ahead for complex slab builds or ground movement protection
 explore our full range of ground heave solutions.