Willmott Dixon has completed a pioneering fire-safety test programme focused on cavity barriers used with Cross‑Laminated Timber (CLT) structures. The initiative addresses a longstanding knowledge gap in how cavity barriers perform in timber-panel construction across wall and floor interfaces.
What was done
- The tests were conducted in collaboration with passive-fire protection specialist Siderise and CLT manufacturer KLH UK.
- They addressed three key interface scenarios:
- CLT walls in vertical configurations using EW-CB 30 cavity barriers (tested to EN 1366-4).
- CLT floor-to-wall horizontal configurations using EW-CB 30.
- CLT floor-to-wall horizontal configurations in rainscreen applications with RH25 90/30 cavity barriers (tested to prEN 1364-6).
- All configurations were tested using “worst-case” conditions, including 100mm five-layer CLT panels, and passed successfully with certified performance.
Why this matters
- Until now, every CLT project involving cavity barriers required bespoke fire-safety assessments, causing design delays, additional cost and uncertainty for architects, contractors and clients.
- The standardised, certified test data now enables CLT projects to specify cavity barrier solutions with confidence, streamline design programmes and reduce technical risk.
- This development supports wider adoption of CLT construction by removing a barrier (no pun intended) in fire-safety compliance and in the integration of low-carbon materials in building projects.
Considerations & Strategic Impact
- While the testing results are a major step, broader adoption will depend on designers, regulators and building-control frameworks recognising and trusting the standard details derived from this work.
- For clients and contractors, the transition means CLT can now compete more favourably with other construction forms — provided the rest of the fire-safety regime (compartmentation, detection, suppression) is also robust.
- The shift may accelerate use of timber in medium-rise and high-rise developments, contributing to sustainability goals in construction — but timber does not eliminate all fire-risk and must be integrated with complementary safety systems.
Final Thought
Willmott Dixon’s work on certified fire-safety testing for CLT cavity-barrier interfaces could mark a turning point for timber construction in the UK. By closing a critical technical gap, the project promotes greater confidence in timber builds, supports sustainability ambitions and streamlines regulatory compliance. The real test now will be how widely and rapidly the industry adopts these standardised details and whether the delivery chain capitalises fully on the opportunity.