Willmott Dixon has commissioned comprehensive fire safety tests for cavity barriers on Cross-Laminated Timber to eliminate a technical gap that has created uncertainty and delays on cross-laminated timber (CLT) projects across the sector.
Conducted in partnership with Siderise and CLT manufacturer KLH, the testing programme provides the ‘first certified solutions for cavity barrier performance in CLT wall and floor applications’. Until now, each CLT project required bespoke fire safety assessments due to the lack of standardised data.
The tests took place at Siderise’s Innovation Centre in Maesteg and examined three common interface scenarios in CLT construction:
- Vertical CLT wall interfaces with the EW-CB 30 cavity barrier (tested to EN1366-4).
- Horizontal CLT floor and wall interfaces with the EW-CB 30 barrier (EN1366-4).
- Horizontal CLT floor and wall interfaces with the RH25 90/30 barrier for rainscreen façades (TGD19 prEN1364-6).
All three configurations passed successfully, including testing with 100 mm five-layer CLT panels to rigorous European standards.
The absence of standard testing had been a challenge across the industry, requiring additional design work and raising uncertainty around compliance. The new results enable architects, engineers and contractors to specify standard cavity barrier details with verified performance data, streamlining design and reducing project risk.
“This testing addresses a genuine technical gap that affects every organisation working with CLT,” said Jessica Winyard, Architectural Technologist at Willmott Dixon. “By collaborating with Siderise and KLH, we’re helping to accelerate low-carbon construction while maintaining robust fire safety.”
The results confirm that Siderise EW-CB and RH25 barriers ‘effectively prevent fire spread through concealed spaces in CLT structures’. The findings are expected to support broader adoption of timber construction by providing tested and certified solutions where uncertainty previously existed.
According to Siderise’s director of Testing and Project Engineering, Chris Mort, ‘the work demonstrates how industry collaboration and investment in research can improve compliance and safety standards across emerging construction methods’.
The test data are now available for use across the sector, supporting the development of safer, lower-carbon buildings with validated fire protection performance.
